Clinical Science ( 1990) 78, 199-206
199
Cation transport across lymphocyte plasma membranes in
euthyroid and thyrotoxic men with and without hypokalaemic
periodic paralysis
VERNON M. S. OH, ELIZABETH A. TAYLOR, SOO-HWA Y E 0
AND
KOK-ONN LEE*
Division of Clinical Pharmacology and Therapeutics and *Division of Endocrinology, Department of Medicine, National University
Hospital, Singapore, Republic of Singapore
(Received 3 May/lO October 1989; accepted 20 October 1989)
SUMMARY
1. To study potassium transport in hypokalaemic
periodic paralysis in a model of striated muscle cells, we
measured specific [3H]ouabain binding (the number of
sodium-potassium pumps), sodium-potassium-pumpmediated (ouabain-sensitive) X6Rb influx and sodiumpotassium-pump-independent (ouabain-resistant ) X6Rb
influx in lymphocytes in vitro.
2. The subjects comprised euthyroid and thyrotoxic
men with hypokalaemic periodic paralysis between
attacks, men with uncomplicated thyrotoxicosis, and
healthy men matched for age and weight.
3. Thyrotoxic patients, both with and without periodic
paralysis, had significantly more lymphocyte sodiumpotassium pumps than normal, and a significantly greater
sodium-potassium-pump-mediated XhRb influx. Antithyroid treatment corrected this defect in patients with
thyrotoxic periodic paralysis. Euthyroid patients with
cryptogenic periodic paralysis had significantly increased
sodium-potassium-pump-mediatedX6Rb+influx, but a
normal number of sodium-potassium pumps.
4. Only untreated thyrotoxic and euthyroid patients
with periodic paralysis showed a significant increase
in sodium-potassium-pump-independent x6Rb+ influx
(5.2k 2.8 and 4.5 1.8 respectively, vs control 2.8 1.0
pmol h - '
ce1ls;meanfsD; P<O.OOl, P<0.005).
5. We conclude that thyrotoxicosis increases the
number and activity of sodium-potassium pumps and
facilitates, but is probably not necessary for, periodic
paralysis. Hypokalaemic periodic paralysis is associated
with an increase in sodium-potassium-pump-independent potassium influx.
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Key words: cardiac glycoside receptors, hypokalaemic
periodic paralysis, lymphocyte, sodium-potassiumadenosine triphosphatase, sodium-potassium-chloride
co-transport, thyrotoxicosis.
Abbreviations: Na , K -ATPase, sodium-potassiumadenosine triphosphatase ( E C 3.6.1.37).
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Correspondence: Dr V. M. S. Oh, Division of Clinical
Pharmacology and Therapeutics, Department of Medicine,
National University Hospital, 5 Lower Kent Ridge Road,
Singapore 05 I 1, Republic of Singapore.
INTRODUCTION
Hypokalaemic periodic paralysis occurs in both euthyroid
and thyrotoxic patients. Periodic paralysis affects some
thyrotoxic patients shortly after exercise or a carbohydrate meal, or both [l].The patient usually has limb
weakness which lasts for 1-36 h (median about 8 h).
Unrecognized or untreated hypokalaemic periodic
paralysis in either type of patient may threaten life
through respiratory failure (V. M. S. Oh, unpublished
work) or, rarely, cardiac arrest [ 11. Although rare among
Europeans, the disease is relatively common among
thyrotoxic Chinese. It occurs some 70 times more often in
men than women. Its prevalence in thyrotoxic Chinese
men has been estimated at between 13% [l]and 25.6%
[21. Cryptogenic hypokalaemic periodic paralysis in
euthyroid patients is clinically similar, clusters in families,
and may have a different aetiology [l, 21. Hypokalaemic
periodic paralysis in thyrotoxicosis is abolished by antithyroid treatment [2], but there is no specific long-term
treatment for such paralysis in euthyroid patients.
The homoeostasis of potassium in the circulating
plasma is due in part to the sodium-potassium-adenosine
triphosphatase ( N a + , K+-ATPase) of the plasma
membrane, the sodium-potassium pump [3]. The
sodium-potassium pump is designated ouabain sensitive
(inhibitable) because cardiac glycosides bind to the Na+,
K+-ATPase and inhibit its activity. Cation transport which
is independent of the sodium-potassium pump is
V. M. S. Oh et al.
200
described as ouabain resistant. The pump accounts for
about 40-80’7’0 of the energy-dependent transport of
potassium into, and sodium out of, the cell (dependingon
the cell type and intracellular sodium concentration) and
helps to maintain the resting potential of the plasma
membrane [4, 51. Both the number of sodium-potassium
pumps [6] and Na+, K+-ATPase activity [7] in striated
muscle cells vary directly with thyroid function. The
sodium-potassium pumps of leucocytes and erythrocytes
are also abnormal in untreated patients with uncomplicated thyrotoxicosis and hypothyroidism ([8-101 and V.
M.S. Oh et al., unpublished work). So the lymphocyte
sodium-potassium pump may be expected to be
abnormal in thyrotoxic, and perhaps also euthyroid,
patients with hypokalaemic periodic paralysis.
Erythrocyte sodium-potassium pumps have been
studied in patients with thyrotoxic periodic paralysis but
the results are inconsistent, perhaps because erythrocytes
are non-nucleated atypical cells. For instance, one group
found that in thyrotoxic periodic paralysis both specific
ouabain binding (an index of the number of sodiumpotassium pumps) and the rate constant of ouabain-sensitive 2ZNa+efflux (an index of sodium-potassium-pumpmediated cation transport) were reduced in erythrocytes
[9], but another group found that neither specific
[3H]ouabain binding nor sodium-potassium-pumpmediated potassium influx was altered [lo]. To our
knowledge, no one has investigated cation transport in
nucleated blood cells from euthyroid or thyrotoxic
patients with hypokalaemic periodic paralysis.
We therefore addressed the following questions. ( 1)
How is potassium transport across the plasma membrane
abnormal in nucleated blood cells, namely lymphocytes,
in hypokalaemic periodic paralysis? (2) Do lymphocytes
have more sodium-potassium pumps, and do their
sodium-potassium pumps transport more cations, in
thyrotoxicosis? (3) Does treatment of thyrotoxicosis
reverse these changes? (4) What is the role, if any, of
sodium-potassium-pump-independent
(ouabain-resistant) cation transport across the plasma membrane in
thyrotoxicosisand thyrotoxic periodic paralysis?
We performed experiments with intact lymphocytes in
vitro to measure sodium-potassium pump numbers,
sodium-potassium-pump-mediated influx of
the
potassium analogue “Rb , and sodium-potassiumpump-independent influx of X6Rb+,in men with thyrotoxic periodic paralysis before and after anti-thyroid
treatment, euthyroid men with periodic paralysis, men
with untreated uncomplicated thyrotoxicosis, and in
healthy men.
Some of the results of this study have been presented
elsewhere in preliminary abstract form [ 111.
comprising 35 men with hypokalaemic periodic paralysis
and 11 with uncomplicated thyrotoxicosis; 26 individuals
were healthy men matched for age and body weight. The
mean age and body weight of the healthy controls were
3 3 . 0 2 ~6.5
~ years and 6 2 . 7 f s ~7.5 kg, respectively.
Although thyrotoxic men tended to be lighter, no significant differences in mean age or weight were found
between any of the subject groups using the two-tailed ftest for non-paired data.
Treatment of subjects
Anti-thyroid treatment was deemed successful when
the thyrotoxic patients became clinically and biochemically euthyroid. Carbimazole treatment, in a standard
regimen of reducing doses, was generally continued for
12-24 months altogether. Some thyrotoxic patients
gained weight during anti-thyroid treatment, but the mean
increase was not statistically significant. All the subjects
were asked not to take any drugs other than those prescribed. All the subjects freely gave their informed
consent before study. The study was approved by the Biological Sciences Research Review Committee of the
National University of Singapore.
Repeat measurements
We followed up the 11 men with uncomplicated thyrotoxicosis for at least 9 months each to ensure that they did
not develop periodic paralysis. Six of these men agreed to
be studied again after treatment for a mean of 15 ( fSD
1.8) weeks with standard doses of carbimazole. Of the 35
patients with hypokalaemic periodic paralysis, 18 were
thyrotoxic men with periodic paralysis before treatment,
of whom eight agreed to be studied again after treatment
of thyrotoxicosis with carbimazole (six men for a mean of
14+s~
1.7 weeks) or 13’1 (two men). Another three men
with thyrotoxic periodic paralysis were studied after, but
not before, anti-thyroid treatment, so that altogether 11
were studied after treatment for 15 fSD 1.6 weeks. The
remaining 14 patients were euthyroid men with cryptogenic hypokalaemic periodic paralysis.
Timing of blood samples
+
METHODS
Subjects
We consecutively studied altogether 72 individual men
(69 Chinese and three Malays) between July 1983 and
September 1988. Forty-six individuals were patients,
All patients, but not the healthy subjects, fasted overnight for an oral glucose tolerance test. Venous blood (60
ml) was sampled from each subject at 08.30 hours on the
day of study. The same procedure was followed for repeat
experiments. Plasma was separated from 20 ml of blood
to evaluate thyroid and renal function in all subjects, and
plasma glucose and insulin concentrations in the patients.
All the patients with thyrotoxic periodic paralysis were
studied 48-72 h after the onset of paralysis, but when
both plasma potassium concentration and muscle power
had become normal. We followed up each of the 14
euthyroid men with hypokalaemic periodic paralysis for
at least 2 years to exclude thyrotoxicosis. Of the latter
patients, two were studied about 48 h after paralysis but
after full clinical and biochemical recovery; the remainder
Cation transport in hypokalaemic periodic paralysis
were studied up to 12 weeks after the last episode of
paralysis. None of the patients with periodic paralysis was
studied during paralysis because all had received potassium chloride shortly after diagnosis.
Criteria for inclusion and exclusion
All subjects had normal plasma urea, creatinine and
electrolytes, and normal 24 h urinary excretion of potassium and sodium, when studied. The euthyroid patients
with periodic paralysis, patients with thyrotoxic paralysis
after anti-thyroid treatment, and the healthy control
subjects all had normal plasma thyroxine concentrations
and free thyroxine indexes. All the patients with periodic
paralysis had plasma potassium concentrations < 3.10
mmol/l (median 2.35 mmol/l, range 1.59-3.10 mmol/l)
during paralysis. No patient had a blood pressure at rest
>,140/90 mmHg (phase 5 diastolic), and none of the
euthyroid patients with periodic paralysis had clinical or
biochemical features which suggested other diseases
commonly associated with hypokalaemia.
Preparation of cells
For each set of experiments we isolated intact lymphocytes from 40 ml of venous blood within 20 min of venesection by centrifugation on the density gradient
Ficoll/sodium diatrizoate [ 121. The lymphocytes were
counted using a Coulter counter. The following
measurements were then completed without knowing the
clinical state of the subjects.
Specific [3H]ouabain binding
We measured the number of sodium-potassium pumps
in the lymphocytes by estimating the maximum specific
binding of ["Hlouabain to the cells in vitro, using an
established technique in which the cells are incubated for
2 h at 37 "C with 25 nmol/l ["Hlouabain in the presence
and absence of 5 pmol/l digoxin (final concentrations) [ 13,
141. Specific ["Hlouabain binding was defined as the
difference between binding in the absence and presence
of digoxin and expressed as fmol/106 cells.
Using Scatchard analysis, we estimated the equilibrium
dissociation constant (K,) of specific ["Hlouabain binding
at different concentrations of unbound ["Hlouabain (5,
7.5, 10, 15, 20 and 25 nmol/l) to lymphocytes [13] from
six untreated thyrotoxic men and 10 matched healthy
men to see if binding affinity was altered by thyroid
function. Each measurement was completed within about
2.5 h (3.5 h for Scatchard experiments).
86Rb+influx
We calculated the activity of lymphocyte sodiumpotassium pumps by measuring the rate of influx
of the potassium analogue 86Rb+ into the cells in vitro,
using an established technique [14]. Briefly, cells were
incubated for 1 h at 37 "C in the presence of an incubation medium containing 8.3 pmol/l x6Rb+ and 4.48
201
mmol/l potassium. This technique assumes that 8hRb+
forms a negligible fraction of the sum total of potassium
and 86Rb+ ions, and that the plasma membrane handlqs
X6Rb+like potassium. The ratio of potassium influx to
HhRb+influx according to the technique is 4488.3/8.3:1,
that is, 540.8:l.
Sodium-potassium-pump-independent (ouabain-resistant) influx of x6Rb+was measured in the presence of 100
pmol/l non-labelled ouabain. Sodium-potassium-pumpmediated (ouabain-sensitive) 86Rb+influx was defined as
the difference between total and sodium-potassiumpump-independent (ouabain-resistant) 86Rb+influx, and
expressed as pmol h-'
cells without conversion to
potassium influx. Each measurement was completed
within about 1.5 h.
Statistical assessment
After ascertaining homogeneity of variance, the values
obtained from different subject groups were compared by
one-way analysis of variance, using the General Linear
Models procedure of the Statistical Analysis System
package (SAS Institute, Cary, NC, U.S.A.). Where
analysis of variance showed a significant difference
between groups, the difference was assessed using the
two-tailed t-test for non-paired samples. Values of K, in
thyrotoxic and healthy men were also compared using the
two-tailed t-test for non-paired groups.
All results are expressed as means SD.
*
RESULTS
The specific binding of [3H]ouabain to lymphocytes (the
number of lymphocyte sodium-potassium pumps) was,
on average, significantly higher before anti-thyroid
treatment in both men with uncomplicated thyrotoxicosis
(by 16.0%) and thyrotoxic men with hypokalaemic
periodic paralysis between attacks of paralysis (by 22.1%)
than in matched healthy men (Table 1). The number of
sodium-potassium pumps became normal after the effective treatment of thyrotoxicosis in men with thyrotoxic
periodic paralysis (Table 1) and men with uncomplicated
thyrotoxicosis (data not shown).
Between attacks of paralysis, specific [3H]ouabain
binding was 4.2% higher in euthyroid men with periodic
paralysis than in the control subjects, but the difference
was not statistically significant (Table 1). So specific
['Hlouabain binding was significantly greater in thyrotoxic
patients only, whether or not they had experienced hypokalaemic periodic paralysis.
The K , of ['Hlouabain binding to lymphocytes was
similar in men with untreated uncomplicated thyrotoxicosis and healthy men [3.61 nmol/l (SD 0.15, ti = 6) vs 3.48
nmol/l (SD 0.17, t z = lo)]. Fig. 1 gives typical Scatchard
plots for these groups of subjects.
Before anti-thyroid treatment, the rates of both total
xfiRb+influx (data not given) and sodium-potassiumpump-mediated xhRb+influx into the lymphocytes were
significantly higher than normal in both uncomplicated
thyrotoxicosis and thyrotoxic periodic paralysis between
V. M. S. Oh et al.
202
Table 1. Specific I3H]ouabain binding to intact lymphocytes from healthy men, men with untreated uncomplicated
thyrotoxicosis, and euthyroid and thyrotoxic men with hypokalaemic periodic paralysis before and after anti-thyroid
treatment
Values are expressed as means k SD. One-way analysis of variance examined the effects of thyrotoxicosis and periodic
paralysis on specific [3HH]ouabain binding: *P< 0.05; **P< 0.01; t P < 0.005; ttP< 0.001. Abbreviation: HPP,
hypokalaemic periodic paralysis.
Specific [3H]ouabain
binding (fmol/ 1Oh cells)
Group 1: healthy men ( I I = 26)
Group 2: untreated euthyroid men with
HPP ( n = 14)
Group 3: untreated men with
uncomplicated thyrotoxicosis ( n= 11)
Group 4: untreated thyrotoxic men with
HPP ( ! I = 18)
Group 5: treated thyrotoxic men with
HPP(n=11)
57.0 k 1.9
65.1 k 3.9
66.1 k 2.2
*
69.6 4.0
5 1.6 f 2.6
Group
comparison
Difference
between means
95% confidence interval
2vs 1
2vs4
3vs 1
3 vs 4
4vs 1
4 vs 5
5 vs 1
5 vs 3
8.0
- 4.5
9.1*
- 3.5
12.6tt
17.9t
- 5.4
- 14.5**,
-0.13 to 16.19
- 13.3 to 4.2
0.2 to 17.9
- 12.9 to 5.9
5.0 to 20.1
8.5 to 27.3
- 14.2 to 3.5
- 24.9 to - 4.0
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121
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J
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Bound [3H]ouabain(fmol/lO" cells)
Fig. 1. Scatchard plots for specific [3HH]ouabainbinding
at six different concentrations of unbound ['Hlouabain to
intact lymphocytes from men with untreated uncomplicated thyrotoxicosis ( 0 )and healthy age- and weightmatched men (0).Each point represents the mean of
typical values from two individual men.
14-
(4
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a6-
attacks of paralysis (Figs. 2a and 3a). Total influx (data
not given) and sodium-potassium-pump-mediated
X6Rb+influx were both similar in thyrotoxic men with and
without periodic paralysis. However, in patients with
thyrotoxic paralysis (Figs. 2a and 3a), sodium-potassiumpump-mediated XoRb+influx was 87.2% greater than normal (17.6k8.7 vs 9.4k3.1 pmol h - '
cells). So the
men with thyrotoxic periodic paralysis had, before antithyroid treatment, not only the most sodium-potassium
pumps, but also the highest rate of sodium-potassiumpump-mediated X6Rb influx.
The rates of sodium-potassium-pump-mediated (Figs.
2a and 3a) and total influx of X6Rb+(data not shown)
were normal after anti-thyroid treatment in men with
thyrotoxic periodic paralysis (Figs. 2a and 30) and men
with uncomplicated thyrotoxicosis (not shown).
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Fig. 2. ssRb+ influx in intact human lymphocytes in
vitro. )(. Sodium-potassium-pump-mediated (ouabainsensitive) sc'Rb+ influx. ( b ) Sodium-potassium-pumpindependent (ouabain-resistant) ""Rb+ influx. The bars
indicate means. 0 , Healthy age- and weight-matched men,
11 = 26; A , euthyroid men with untreated hypokalaemic
periodic paralysis; ) I = 14; 0, men with untreated uncomplicated thyrotoxicosis, ) I = 11; V, men with thyrotoxic hypokalaemic periodic paralysis before anti-thyroid
treatment, I ? = 18; V, men with thyrotoxic hypokalaemic
periodic paralysis after anti-thyroid treatment given for an
average of 15 weeks, I I = 11.
Cation transport in hypokalaemic periodic paralysis
P< 0.001
-
10-
7
5-
h
y1
d
e,
-z
I
2
0-
t t 1
4vs 1
E,
v
-5-
.5
?
0
-10 _I
P< 0.001
P< 0.005
4
1 t
< 0.005
2vs1
t
2 vs 4
vsl
4vs5
3 vs 4
5vs1
5vs3
v,
P < 0.005
5 vs 3
4
x
Fig. 3. Ninety-five per cent confidence intervals for
differences between the mean values of sflRb+ influx
in intact human lymphoc tes iri v i m . ( ( I ) Sodiumpotassium-pump-mediated [ouabain-sensitive) sc'Rb+ influx. (b) Sodium-potassium-pump-independent (ouabainresistant) sf'Rb+ influx. 1, Healthy age- and weightmatched men, 11=26; 2, euthyroid men with untreated
hypokalaemic periodic paralysis, I I = 14; 3, men with
untreated uncomplicated thyrotoxicosis. I I = I I ; 4, men
with thyrotoxic hypokalaemic periodic paralysis before
anti-thyroid treatment, I I = 18; 5 , men with thyrotoxic
hypokalaemic periodic paralysis after anti-thyroid treatment given for an average of 14 weeks, I I = 1 1.
Sodium-potassium-pump-mediated X"Rb+ influx was
significantly (70.2%) higher in lymphocytes from
untreated euthyroid patients with hypokalaemic periodic
paralysis than in cells from the healthy control subjects
cells), although the
(16.0 f 5.5 vs 9.4 f 3.1 pmol h- I
number of sodium-potassium pumps was normal (Table
1, Figs. 2a and 3a).
.
203
The ratio of sodium-potassium-pump-mediated x6Rb+
influx to specific ["Hlouabain binding represents the number of X6Rb+ions which each sodium-potassium pump
transports per h. This index of the cation transport of
individual sodium-potassium pumps was significantly
higher than normal in all untreated patients, and remained
so in patients with thyrotoxic periodic paralysis after their
thyrotoxicosis had been effectively treated (Table 2).
Sodium-potassium-pump-independent influx of potassium, represented by ouabain-resistant sf'Rb+ influx, was
significantly greater in both euthyroid men with periodic
paralysis (by 86%) and thyrotoxic men with periodic
paralysis before anti-thyroid treatment (by 6 1%) than
normal (5.2f2.8 and 4.5 f 1.8 vs 2 . 8 f 1.0 pmol h-'
lo-" cells) (Figs. 2b and 36). Sodium-potassium-pumpindependent influx of XbRb+decreased to normal after
treatment in the men with thyrotoxic periodic paralysis.
By
contrast, sodium-potassium-pump-independent
X6Rb+influx was normal in patients with untreated
uncomplicated thyrotoxicosis (Fig. 3 b).
None of the patients with thyrotoxic periodic paralysis
who remained clinically euthyroid after anti-thyroid treatment has reported paralysis to date. In two such patients a
repeat study of their lymphocytes 1.2 and 1.8 years after
carbimazole treatment began showed normal rates of
total, sodium-potassium-pump-independent and sodiumpotassium-pump-mediated X6Rb+influx. One patient with
thyrotoxic paralysis, who stopped taking carbimazole
after 5 months, again had acute paralysis; sodiumpotassium-pump-independent sf'Rb+ influx was again
increased in his lymphocytes.
DISCUSSION
Our results show that intact lymphocytes from men with
thyrotoxicosis, whether or not complicated by hypokalaemic periodic paralysis, had significantly more
sodium-potassium pumps (Table 1) and a significantly
higher sodium-potassium-pump-mediated
influx of
xnRb+before anti-thyroid treatment (Fig. 3a). Sodiumpotassium-pump-mediated X6Rb+influx was also significantly higher in lymphocytes from euthyroid men with
periodic paralysis than in cells from healthy men (Fig. 2a),
although the number of sodium-potassium pumps per
cell was similar in these subject groups (Table 1). Only
m e n , with periodic paralysis, whether euthyroid or
untreated thyrotoxic, showed a significant increase in
sodium-potassium-pump-independent
(ouabain-resistant) influx of XhRb+between attacks of paralysis (Fig.
3b).
As the affinity of [3H]ouabain binding ( K , ) was not
altered by thyrotoxicosis in the present study, we believe
that differences in specific ["Hlouabain binding reliably
reflected differences in the number of sodium-potassium
pumps.
The greater number of sodium-potassium pumps per
cell, and the higher sodium-potassium-pump-mediated
influx of xf'Rb+ which we found in lymphocytes from
patients with untreated thyrotoxicosis, whether o r ncit
complicated by hypokalaemic periodic paralysis (Table
V. M. S. Oh et al.
204
Table 2. Ratio of sodium-potassium-pump-mediated(ouabain-sensitive) “Rb+ influx to specific [3Hjouabain binding in
healthy men, men with untreated uncomplicated thyrotoxicosis, and euthyroid and thyrotoxic men with hypokalaemic
periodic paralysis before and after anti-thyroid treatment
Values are expressed as means +_ SD. One-way analysis of variance assessed the effects of thyrotoxicosis and periodic
paralysis on sbRb+ influx of individual sodium-potassium pumps: *f’< 0.05; ttf’< 0.00 1. Abbreviation: HPP,
hypokalaemic periodic paralysis.
Sodium-potassium-pump-mediated
a‘’Rb+ influx/specific
13H]ouabainbinding ( h - ’)
Group
comparison
Difference
between means
95% confidence interval
2vs 1
2vs4
3vs 1
3 vs 4
82tt
0
63*
- 19
37 to 127
- 48 to 48
14to112
-71 to33
~~~
Group 1: healthy men ( / I = 26)
Group 2: untreated euthyroid men
with HPP ( n = 14)
Group 3: untreated men with
uncomplicated thyrotoxicosis
(n=ll)
Group 4 untreated thyrotoxic
men with HPP ( 1 1 = 18)
167f51
249 f 87
249 k 75
4vs 1
4vs5
82ti
20
40 to 123
- 32 to 12
Group 5: treated thyrotoxic men
with HPP ( t i = 1 1 )
229 f 70
5 vs 1
5 vs 3
62*
-1
13tollO
-59 to 56
230 f 62
l), is due to the increased action of thyroid hormones on
cells perse [15,16]. Similar changes occur in mixed leucocytes from untreated thyrotoxic patients [S]. More
sodium-potassium pumps per cell are also found in
human striated muscle cells obtained by biopsy from
thyrotoxic patients [6]. The thyroid hormones probably
act on the P,-adrenoceptor, which modulates sodiumpotassium-pump-mediated cation transport [31.
The changes in the sodium-potassium pump of leucocytes due to thyrotoxicosis are similar, and those of
erythrocytes are opposite, to the changes in the pump of
striated muscle cells [6-8]. We therefore believe that the
sodium-potassium pump of blood lymphocytes reliably
models that of striated muscle cells in disorders of transport of monovalent cations. The use of lymphocytes
obtained by venesection saves the patient the discomfort
and risks of muscle biopsy.
The number of “Rb+ ions that each sodium-potassium pump transports per h, which represents the cation
transport of individual sodium-potassium pumps, is
increased in untreated uncomplicated thyrotoxicosis
(Table 2). Each pump might be stimulated by an increase
in intracellular sodium concentration [5], as has been
found in erythrocytes [8-101. Although we did not
measure cell sodium, however, intracellular sodium concentration is not increased in mixed leucocytes from
patients with untreated uncomplicated thyrotoxicosis [S].
So the enhancement in cation transport of individual
sodium-potassium pumps (Table 2) is probably also due
to the increased action of thyroid hormones on the
lymphocytes.
The successful treatment of thyrotoxicosis with carbimazole or 13’1 abolishes periodic paralysis in patients
with thyrotoxic hypokalaemic periodic paralysis ([1, 21
and in the present study). Moreover, such treatment
corrects the increases in the number of sodiumpotassium pumps per cell and in the sodium-potassiumpump-mediated 8hRb influx in patients with thyrotoxic
+
periodic paralysis (Table 1, Fig. 2a). However, antithyroid treatment reduces sodium-potassium-pumpmediated cation transport proportionately less than the
number of pumps, so that after treatment individual
pumps still transport more cations than normal (Table 2).
As sodium-potassium-pump-mediated X6Rb influx is
also increased in euthyroid patients with cryptogenic
periodic paralysis, these results suggest that the abnormality in the sodium-potassium pump due to thyrotoxicosis facilitates, but is not necessary for, hypokalaemic
periodic paralysis.
The transport of potassium and sodium across the
plasma membrane is both mediated through the
sodium-potassium pump (ouabain sensitive) and independent of this pump (ouabain resistant). In the present
study only men with periodic paralysis, whether euthyroid
or thyrotoxic, showed a significant increase in
sodium-potassium-pump-independent
X6Rb+ influx
before anti-thyroid treatment (Figs. 2b and 3b). By
contrast, patients with untreated thyrotoxicosis but
without paralysis had normal sodium-potassium-pumpindependent influx of x6Rb+(Figs. 2b and 3b), as shown
in an earlier study [S]. The onset of hypokalaemic
paralysis in both euthyroid and thyrotoxic patients is
therefore linked to an increase in the sodium-potassiumpump-independent component of basal potassium influx.
It is also possible that an increase in sodiumpotassium-pump-independent potassium influx promotes
paralysis, on the following evidence. First, the successful
anti-thyroid treatment of patients with thyrotoxic periodic
paralysis removes both the defect in sodium-potassiumpump-independent xhRb+influx and the risk of paralysis.
Secondly, none of those treated patients who remained
clinically euthyroid have reported paralysis to date. After
successful anti-thyroid treatment, however, patients with
thyrotoxic periodic paralysis whose thyrotoxicosis
relapses may again experience paralysis [ 1, 21. When one
patient in the present study relapsed with thyrotoxic
+
Cation transport in hypokalaemic periodic paralysis
periodic paralysis, sodium-potassium-pump-independent
"Rb+ influx was again increased in his lymphocytes.
However, an increase in sodium-potassium-pumpindependent X6Rb+influx may simply be a marker for
periodic paralysis.
In a preliminary study in four healthy subjects we had
not found a consistent effect of a meal on lymphoctye
sodium-potassium pumps (V. M. S. Oh et al., unpublished
work). However, a 55% carbohydrate meal significantly
enhanced ouabain-sensitive 22Na+efflux in mixed normal
leucocytes in one study [17], and glucose intake acutely
increased both specific [3H]ouabain binding and total
shRb+ influx in mononuclear leucocytes in another [18].
In the present study the patients, but not the healthy
subjects, were fasting when studied. Had the patients also
fed before study, their lymphocytes would probably
have shown even more sodium-potassium pumps and a
greater total RdRb+influx. So we may have underestimated the true differences in both the number of
cellular sodium-potassium pumps and in sodiumpotassium-pump-mediated and sodium-potassium-pumpindependent influx of X6Rb+,between the patients and
their healthy controls.
The sodium-potassium-pump-independent (ouabainresistant) influx of potassium in lymphocytes is the sum
of frusemide-sensitive sodium-potassium-chloride cotransport [ 19,201 and the frusemide-resistant inward leak
of potassium. We could not determine which of these
transports was overactive in patients with thyrotoxic
paralysis, because too much blood would have been
needed for the experiments.
Although hypokalaemic periodic paralysis is associated
with exercise, meals, or both [l],the immediate trigger for
paralysis is unknown. For instance, a rise in the plasma
glucose concentration, which physiologically increases the
plasma concentration of insulin during and after a meal,
or an increase in the plasma concentrations of adrenaline
and insulin during exercise, might each acutely amplify
the entry of potassium into cells [l, 21. On top of the
increase in the basal influx of potassium, both
sodium-potassium-pump-mediated
and
sodiumpotassium-pump-independent, these mechanisms might
reduce the plasma concentration of potassium enough to
hyperpolarize the plasma membrane (sarcolemma) of
striated muscle cells, thereby starting paralysis. However,
exercise or a meal each alters the plasma concentrations
of so many endogenous substances that the trigger has not
been conclusively identified by experiment. Ethical
principles constrain experiments in vivo to elucidate the
trigger, as severe paralysis may threaten life.
The rapid disposition of potassium from the plasma of
patients during acute paralysis is also unexplained.
Twenty-four hour urinary and faecal collections of potassium which include the attack are usually normal in such
patients, suggesting that potassium is not lost in the urine
or faeces [ 2 ] . One hypothesis is that the sodiumpotassium pump, under the influence of B,-adrenoceptors, drives potassium from the plasma into the cells of
striated muscle or the liver, for instance. Some experimental evidence from rat striated muscle [3] and whole
205
human subjects [21, 221 supports this hypothesis. The
results of the present study suggest that an increase in
sodium-potassium-pump-independent
transport
is
associated with the massive entry of potassium into cells.
We conclude that untreated thyrotoxic patients,
whether or not they experience hypokalaemic periodic
paralysis, have more lymphocyte sodium-potassium
pumps and a higher sodium-potassium-pump-mediated
influx of potassium than normal when studied between
attacks of paralysis. Thyrotoxicosis facilitates, but is
probably not necessary for, periodic paralysis. An
increase in the basal sodium-potassium-independent
influx of potassium is associated with periodic paralysis in
both euthyroid and thyrotoxic patients. Further experiments ex vivo should aim at elucidating the mechanism of
amplification of potassium influx at the onset of paralysis.
ACKNOWLEDGMENTS
We thank Soh-Bee Ye0 and Chay-Seam Hay for their
careful technical assistance. The study was supported by a
research grant (no. RP 540085) provided by the Biological Sciences Research Review Committee of the National
University of Singapore.
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