Clinical Science (1995) 88, 695-700 (Printed in Great Britain)
695
Effect of extracellular potassium concentration on the
sodium-potassium pump rate in human lymphocytes
George D. WEBB*, Elizabeth A. TAYLOR?, Vernon M. S.
OH?,Soh-Bee YEOt and Leong L. NG$
*Department of Molecular Physiology and Biophysics, University of Vermont, College of
Medicine, Burlington, Vermont, U.S.A., ?Division of Clinical Pharmacology and Therapeutics,
Deportment of Medicine, National University Hospital, Singapore. and $Department of Medicine
and Therapeutics, University of Leicester, School of Medicine, Leicester, U.K.
(Received
12 September 1994/10 February 1995; accepted 23 February 1995)
~~~
1. The purpose of this study was to determine
whether physiological changes in extracellular free
[K'] cause significant changes in the Na'-K'
pump
rate and intracellular free [Na'].
2. The Na+-K' pump rate was measured in human
lymphocytes by determining ouabain-sensitive "Rb'
influx at several concentrations of K'. The Na'-K'
pump rate increased within the physiological range of
extracellular free [K'] (Kl/z = l.Smmol/l).
3. To test the hypothesis that elevation of extracellular free [K' ] reduces intracellular free [Na']
rapidly, which in turn then slows the pump rate
during experimental incubations, lymphocyte intracellular free [Na'] was measured using the fluorochrome sodium-binding benzofuran isophthalate. With
larger elevations of extracellular free [K'], intracellular free [Na'] dropped more rapidly. Thus
previous discrepancies among determinations of KII,
may be the result of variations in incubation times,
which can skew the pump rates measured during
incubations in various extracellular free [K'] values.
Steady-state intracellular free [Na'] varied inversely
with extracellular free [K'].
INTRODUCTION
The Na+-K+ pump (Na', K+-ATPase, EC
3.6.1.37) transports N a + out of the cell and K + into
the cell. Variations in extracellular free [K']
([K'],) affect the Na+-K+ pump rate. It is important to know the magnitude of this effect within the
physiological range of plasma potassium, because
many cell functions depend on the Na'-K+ pump.
If the effect is appreciable, it has important clinical
implications, because the plasma (and interstitial)
concentration of K + is subject to acute and chronic
changes. Studies of erythrocytes have found that the
half-maximum Na+-K+ pump rate occurs at a
[K'], of 1.8-2.0mmol/l (the 'KIIZ') [l-31.
Leucocytes may be more representative of most
other body cells than are erythrocytes because, like
most other cells, leucocytes have a nucleus and
mitochondria, and they pump N a + and K' about
50 times faster than erythrocytes [4, 51. Leucocytes
appear to have a mixture of the different isoforms of
the Na+-K+ pump [6] that may more closely
resemble the mixture found in cells which are
important for determining blood pressure, such as
vascular smooth muscle, which apparently expresses
all three isoforms of the catalytic subunit [7].
Erythrocytes express only the a,-isoform of the
catalytic subunit of the Na+-K+ pump [8], whereas
both a1 and ag are expressed in leucocytes [9].
Previous studies in which the Kllz for K + activation of the human leucocyte Na+-K+ pump has
been determined have produced conflicting values;
in one study the Kl12 was found to be 1.7mmol
K+/1 [lo], while in another study Kl12 was only
0.6 mmol/l [ 113. Physiological changes in the
plasma K + concentration would have a considerable effect on the Naf-Kf pump rate if the Kllz is
1.7mmol/l, but not if the KIIz is only 0.6mmol/l.
The discrepancy between the two values of K 112
might be due to the difference in the incubation
times (10 versus 60min) used to determine the
Na+-K+ pump rate in the two studies. In a study
of cultured rat liver cells, changes in [K'], rapidly
altered the intracellular free "a+] ([Na+Ii), which
itself affects the pump rate [lZ]. The effect is
thus the
especially pronounced at higher [K'],;
measured pump rate will be reduced proportionally
more at high [K'],
than at low [K'],,
unless
incubation times are short. This effect should cause
the apparent K l l z to decrease when longer incubation times are used.
To test this explanation for the low apparent Kllz
obtained when lymphocytes were incubated for
60min [ll], in the current study the K I p was
determined using the same techniques, but wlth the
incubation time reduced to 8 min. In addition, the
second-to-second changes in [Na' Ii, after a given
change in [K'],,
were monitored using human
lymphocytes that contained a sodium-sensitive
fluorescent dye. This paper describes the results.
Key words: leucocytes, lymphocytes, Na'-K +-exchanging ATPase, ouabain, potassium.
Correspondence: D r George D. Webb, Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Given Building, Burlington, VT 05405,
U.S.A.
696
G. D. Webb et al.
METHODS
Subjects and lymphocyte preparation
The subjects for the lymphocyte studies were
healthy subjects (five men, four women), who gave
their informed consent to donate their blood. The
protocol received ethical approval from the Biological Science Research Review Committee of the
National University of Singapore and from the
Leicestershire Health Authority Ethics Committee.
At approximately 09 00 hours, 50 ml of venous
blood was slowly drawn into a heparinized syringe,
and the lymphocytes were isolated by discontinuous
density-gradient centrifugation as previously described [13, 141, and washed with RPMI-1640.
MRb influx experiments
The RPMI-washed cells were washed and suspended in K+-free 'Ringer's solution' (KFR), which
contained (in mmol/l): NaCl, 118.3; Na,HPO,,
13.82; NaH,PO,, 3.25; CaCl,, 1.27; MgSO,, 1.19;
and glucose, 5.5 (pH adjusted to 7.4). The total time
in KFR (including wash times) before adding 86Rb
for influx measurement was 47min. The cell concentrations of the suspension were determined with a
Coulter counter. The contamination with erythrocytes averaged 22%. Since erythrocytes pump K + at
about 1/50th of the rate for lymphocytes [4], 99.4%
of the ouabain-sensitive a6Rb+ uptake was into the
leucocytes. The intra-assay coefficient of variation
was 6% in our measurement of "Rb+ influx [14],
therefore a 0.6% erythrocyte correction was deemed
unnecessary.
The method for measuring ouabain-sensitive
86Rb+ influx was the same as described previously
[14], except that the ouabain-treated cells were
preinhibited by exposure to 4.6 x lo-, mol/l ouabain
(in KFR) for 5min and then diluted by adding
86Rb+ together with KCl (substituted for NaCl in
KFR) at concentrations which resulted in final
[K'], values of 1, 2.5, 4.5 or 8.0mmol/l and a final
ouabain concentration of 2 x 104mol/l (the same
procedure was used for the zero ouabain cells).
Quadruplicate tubes were filled in both forward and
reverse orders; the average incubation time (at 37°C)
for each of the four tubes was 8min (two a little
longer and two a little shorter). The incubation was
terminated by agitating the tubes in a water and ice
mixture for 1 min before cold centrifugation.
Corrections were made for the amount of intracellular "Rb+ lost during incubation (back-flux)
and during washing procedure (required to remove
extracellular 86Rb+).It has been demonstrated that
the Na+-K+ pump transports 86Rb+ in exactly the
same way as 42K+ [l5], therefore the 86Rb+ counts
were converted into an equivalent amount of K + by
equating the number of c.p.m./ml in the incubation
solution to the amount of K+/ml. To obtain the
amount of K + influx per litre of cells, we calculated
the total cell volume per tube by multiplying the
number of lymphocytes by 230fl. The average
volume of adult human lymphocytes has been determined to be 233 (SD 29) fl from direct visual
measurements of cellular cross-sectional area [161,
and this agrees well with our volume measurements
using the Coulter counter to estimate mean cell
diameter.
Ouabain-binding experiments
The technique for determining the number of
ouabain binding sites has been described [13, 141.
Lymphocytes were incubated for 2 h at 37°C in
KFR containing 100 nmol/l C3H]ouabain, with and
without unlabelled digoxin 20 pmol/l. Non-specific
ouabain binding averaged 3% of the total binding.
Experiments using several concentrations of
C3H]ouabain showed that 100nmol/l resulted in
close to the maximum amount of ouabain binding.
lntracellular Na' measurements using sodium-binding
benzofuran isophthalate (SBFI)
The method for measuring "a+], with SBFI has
been described by Harootunian et al. [17]. Following isolation of the lymphocytes, the remaining
erythrocytes were lysed with a 10-s distilled water
shock, which does not damage the lymphocytes [4].
The lymphocytes were loaded with the N a + sensitive fluorophore SBFI acetoxymethyl ester
(Sigma, St Louis, MO, U.S.A.), as described by
Harootunian et al. [17]. Ninety per cent of the cells
were then resuspended in K+-deficient Hepesbuffered saline composed of (in mmol/l) NaCI, 140;
KCl, 0.1; CaCl,, 1.8; MgSO,, 0.8; glucose, 5; Hepes,
15; and 10% dialysed fetal calf serum, pH adjusted
to 7.4. The low concentration of K + slowed the
Na+-K+ pump, thus allowing intracellular N a + to
accumulate.
Ten per cent of the cells were incubated in
RPMI-1640 medium to be used for calibration.
After incubation for 1 h to allow hydrolysis of all
the acetoxymethyl groups, the RPMI-treated cells
were resuspended in Na+-free isotonic KCl buffer
containing (in mmol/l), KCl, 140; CaCl,, 1.8;
MgSO,, 0.8; glucose, 5; Hepes, 15, pH 7.4. This
suspension was placed in a cuvette in a dual grating
fluorometer (Deltascan, Photon Technology International, South Brunswick, NJ, U.S.A.), set at 37°C.
Fluorescence emission was determined at 500 nm
(10 nm slit width), with excitation gratings set at 340
and 385 nm (5 nm slit widths). Emission ratios were
determined every 200ms. The 340/385nm ratio is a
measure of the intracellular N a + concentration,
independent of the amount of dye loading or
bleaching, and independent of the cell number. This
ratio was calculated by computer after correcting
for autofluorescence of cells not loaded with SBFI.
After obtaining a stable reading for about a
minute in the Na+-free KCI buffer, the ionophore
Extracellular potassium and Na+-K+ pump rate
697
3.5
.-0
3.0
8
a,
?? 2.5
8
E
I
s
L n
2.0
1.5
Na+ Ommol/l
I
0
200
400
Time
600
800
(I)
0
gramicidin 4 pmol/l was added to permeabilize the
cells to monovalent cations. After about 5min of
exposure to gramicidin, intracellular Na' was depleted. Extracellular Na' concentration was then
raised by adding appropriate volumes of isotonic
NaCl buffer, stepwise, to raise [Na'], to 5, then 10,
20, 40 and finally 80pmol/l, allowing "a'],
to
equilibrate before each addition (see Fig. 1).
Note that "a'],
dropped very slowly in the KCl
buffer until gramicidin was added. A standard curve
of Na' concentration against the 340/385 nm fluorescence ratio was entered into the computer from
these calibration data.
The cells which had been incubated in
K+-deficient Hepes-buffered saline achieved intracellular Na' concentrations ranging from 50 to
60 mmol/l within 3 h. These cells were resuspended
(0.1 mmol K+/1) Hepesin fresh K'-deficient
buffered saline and equilibrated for 5min in the
fluorometer. The intracellular Na' concentration
remained stable over this period. Isotonic KCl was
added in a volume sufficient to achieve a desired
[K'],.
Readings of "a+],
(converted from the
340/385 nm ratio by computer using the previously
obtained calibration curve) were obtained every
200ms over the next 20min. This was repeated for
[K'],
of 1, 2.5, 4, 8 and 16mmol/l in random
order. The cells usually remained viable (and
unclumped) long enough to allow repetition of some
or all concentrations, yielding nearly identical
curves. This allowed us to study, in real time, the
net change in "a+], resulting from the addition of
K' (e.g. Fig. 4). To verify that the net changes in
[Na'], in Na'-loaded cells, after the addition of
extracellular K', were mediated primarily by the
Na+-K' pump, the pump was inhibited by adding
ouabain lOOnmol/l before the addition of K'. This
2
4
8
6
V+I0 (mmol/l)
Fig. 1. Fluorescence intensity ratio for the excitation wavelengths of
340 and 38Snm is plotted versus time. Human lymphocytes were
preloaded with the sodium-binding fluorescent dye benrofuran isophthalate
and suspended in a zero Na+ buffer. A t the time indicated, the cells were
permeabilized to monovalent cations with gramicidin. Then the Na"
concentration was increased stepwise as indicated.
Fig. 2. Na+-K+ pump rate (expressed as the ouabaimensitive K+
influx rate calculated from %b+ influx) versus extracellular K +
concentration in human lymphocytes. Points are the means of six
subjects (each subject was tested in quadruplicate). The curve is the best
computer fit to the equation y=ox/(b+x).
Table 1. Comparison of ouabaimensitive K+ influx rate with the
number of ouabain binding sites. The ouabain-sensitive K" influx rate
in mmoll-I cells h-l, was calculated from the "Rb+ uptake during an
Bmin incubation in K + 4.5mmol/l. Values are the means of quadruplicate
parallel experiments. The numbers of ouabain binding sites are the means of
triplicate parallel experiments.
Subject
OuabaiMensitive K + influx rate
(mmoll-I cells h-l)
Ouabain binding sites/cell
I
172
I18
261
I09
I70
429
37 OOO
60 OOO
57 OOO
34 000
44000
131 OOO
2
3
4
5
6
abolished the fall in intracellular Na' concentration
when [K'], was raised and, in some cases, led to a
further slight rise in intracellular Na' concentration
(data not shown).
RESULTS
The effect of [K'], on the Na'-K'
pump rate
(determined as the ouabain-sensitive 86Rb' influx
rate) in human lymphocytes, using 8 min incubation
times, is shown in Fig. 2.
In the equation for the curve in Fig. 2, 'b' the
[K'],
at half 'Vmai (K1,J, was lSmmol/l. The
curve in Fig. 2 shows that small deviations in [K'],
from the normal concentration of 4 mmol/l produce
biologically significant changes in the Na'-K'
pump rate.
Table 1 shows the individual values for both
Na+-K+ pump rate, when the cells were in a
physiological solution containing 4.5 mmol/l K +,
G. D. Webb et al.
698
'
=
>
-+d
z
28
g
-c
70-
60-
/-
50403020-
10
-
0-
OJ
r
8
I
0
50
100
I
I
1
I
150
200
250
Time of K + depletion (min)
300
350
Fig. 3. lntracellular N a + concentration in human lymphocytes as
measured by the fluorescence ratio of the intracellular sodiumbinding dye benzofuran isophthalate (see Fig. I).At time zero, the
cells were transferred to a buffered saline containing 0.1 mmol/l K+.
Samples of the suspension were taken at later times as indicated.
and for the number of ouabain binding sites for the
six subjects whose data were used in Fig. 2.
The pump rate does not appear to be directly
proportional to the number of ouabain binding
sites, possibly because of differences in "a'],.
Although the pump rate varies considerably
between individuals, the shapes of the individual
curves of pump rate versus [K'],
were similar.
When K,/, was calculated from each individual
curve, the mean was 1.52mmol/l and the standard
error of the mean was 0.23. This mean, resulting
from our current 8 min incubations, is significantly
different (Pe0.02) from the mean KII, of 0.65
(SE 0.10) mmol/l calculated the same way from the
data generated using 60-min incubations [ l l , 181.
The [Na'Ii in human lymphocytes progressively
increases after the [K'], is reduced to 0.1 mmol/l
(Fig. 3).
We found that, after about 5 h, "a'],
reached a
steady state of about 60 mmol/l with the extremely
slow Na+-K+ pump rate that is sustained by a
[K'], of 0.1 mmol/l. We also found that when we
suspended the cells in a solution containing no
extracellular K +, the cells usually become irreversibly damaged within 2 or 3h. After the cells
containing the Na'-sensitive fluorescent dye had
been in [K'], of 0.1 mmol/l for over 3 h, an aliquot
of cells was placed in the fluorometer and [K'],
was increased to one of five selected concentrations
(in random order) while "a'],
was measured. The
results of such experiments on a representative
subject are shown in Fig. 4.
To facilitate comparisons, the curves in Fig. 4
were chronologically superimposed by computer so
that time zero was redefined as the time at which
[Na'], became 52mmol/l, a little less than the
starting value. "a'],
dropped more rapidly the
higher the [K'],.
The rate of change in [Na'],
decreased with time, and for each [K'], value the
I
0
I
200
400
600
800
loo0
1200
1400
Time (s)
Fig. 4. Superimposed computer plots of five experiments on a
representative subject's lymphocytes showing [Na'li measured
with intracellular sodium-sensitive fluorescent dye after raising
[K'], to the level indicated. The cells had previously been incubated in
[K'], 0.1 mmol/l t o raise "a+]; to above 55mmol/l. The curves were
superimposed by computer so that time zero was redefined as the time at
which "a+], became 52mmol/l, and are plotted from that point on.
[Na+]i 50 mmol/l
[Na+]i 45 mmol/l
[Na+]i 40 mmol/l
[Na+]i 35 mmol/l
[Na+]i 30 mmol/l
...._...........--=[Na+]i 25 mmol/l
[Na+]i 20 mmol/l
Fig. 5. N e t Na' efflux rate versus [K'], for selected "a'],
values. ?he curves were generated from the data shown in Fig. 4. When
the SD is shown, the values are on the same subject's cells.
"a'],
appears to progress towards a different
steady-state level. The slope of the curves at any
point gives the rate of net Na' efflux at that point.
These slopes were determined by computer at
selected values of [Na'],, using the curves shown in
Fig. 4, and are plotted in Fig. 5.
For all the "a'],
values selected, the rate of net
Na' efflux increases when [K'], is raised above
the physiological concentration of 4 mmol/l (Fig. 5).
The net Na' efflux rate appears to approach a
maximum when [ N a f l i is 50mmol/l and [K'], is
16 mmol/l.
DISCUSS10N
These results show that changes in plasma K'
concentration within the physiological range will
cause significant changes in the cellular Na'-K+
pump rate and "a'],
in human lymphocytes, and
presumably in most cells. [Na'], approaches a
steady-state value that depends (inversely) on [K'],
Extracellular potassium and Na+-K+ pump rate
concentration (Fig. 4). Thus, the plasma K + concentration sets [Na'li through its effect on the
Na+-K+ pump rate. This has important physiological consequences, since there are several
Na+-dependent co- and counter-transport systems
in cell membranes.
The Kllz of 1.5mmol/l for K + activation of the
Na+-K+ pump found here (Fig. 2), is 2.5 times
greater than the K l 1 2 of 0.6mmol/l found earlier
[ll] using the same technique, but with a longer
incubation time (60min compared with the present
8min). The upper curve in Fig. 5 provides an
approximate, near-instantaneous (200ms) determination of pump rate for various [K'],
values.
The Kll, for this curve is 2.0mmol/l, consistent with
the trend for a larger KIl2 when the incubation is
shorter. The other curves in Fig. 5 do not accurately
reflect the pump rate because, as
falls, the
net Na' efflux rate falls, partly because of the
increasing net 'passive' influx (i.e. falling total
passive efflux). Thus, the net Na' efflux rate
approximates the pump efflux rate only at high
[Na'Ii when net passive Na+ flux is near zero.
The finding of larger K,,, values when incubation
times are shorter may be the result of the more
rapid decline of
in higher [K'],, as seen in
Fig. 4. The K , , , for activation of the Na+-K'
pump by intracellular Na' is about 12mmol/l [19].
Based on the data of Fig. 4, if cells are incubated in
lmmol/l [K'], for 8min, [Na'li will drop from
52mmol/l to 42mmol/l. Thus the pump will be
nearly maximally stimulated by Na" throughout the
8min incubation. In contrast, after 8min in
16mmol/l [K'],, the pump will be only about 70%
activated by the [Na+Ii of 22 mmol/l. Thus
16mmol/l [K'], will appear to be somewhat less
effective in activating the Na+-K+ pump than it
really is. This effect will be accentuated with longer
incubations, leading to a lower apparent K l l z .
It is possible that KlI2 for K' activation might
vary with [Na+Ii independent of incubation time,
but this appears not to be the case. In the present
study (as in [ll]) the cells used to produce the data
for Fig. 2 were preincubated for 47min in KFR,
raising [Na+li to about 23 mmol/l compared with
the normal of 14mmol/l (based on Fig. 3). Nevertheless, the present value for K
was very close to
the value obtained by Hilton et al. [lo], who used
leucocytes with normal [Na+Ii and a similar incubation time. In voltage-clamped guinea pig ventricular myocytes with [Na+li controlled at 50 mmol/l,
the Kllz for extracellular K + activation of the
Na+-K+ pump was found to be 1.5mmol/l [20],
identical to the value from Fig. 2 where [Na+li was
only 23 mmol/l
The sensitivity of the pump to K' may underlie
several physiological phenomena. One example is
active hyperaemia, in which arteriolar smooth
muscle relaxes independently of nervous or hormonal input when a tissue such as skeletal muscle is
active. In an exercising muscle, the extracellular K +
699
concentration may reach 10-15mmol/l as a result of
the K + released from the skeletal muscle fibres by
the action potentials [21, 221. The data in Figs. 2
and 5 suggest that changing [K'],
from 4mmol/l
to 12mmol/l will increase the Na+-K+ pump rate
by about 25% in the surrounding cells. It has been
found that increasing [K '1, (in the physiological
range) causes a reduction in [Na+Ii in cultured
vascular smooth muscle cells [23]: it is likely that
this also occurs in uiuo. This will speed up the
extrusion of Ca2+ by the Na+/Ca2+ exchanger
[24], causing relaxation and increased blood flow.
In addition, faster Na+-K+ pumping will cause
hyperpolarization, which will decrease the average
open time of voltage-sensitive Ca2+ channels [25],
also leading to relaxation of vascular smooth
muscle.
These same mechanisms, which may partly
explain active hyperaemia, may also be partly
responsible for the negative correlation between
blood pressure and plasma K + concentration seen
in several human populations [ll, 26-30]. A review
of the placebo-controlled, double-blind studies of
oral KCl supplementation showed that KC1 supplementation reduces the blood pressure and usually
increases plasma K + concentration [3 11. Additional
dietary K + in natural foods also appears to raise
plasma K' and lower blood pressure [30, 321. The
mechanisms by which the cellular Na+-K+ pump
rate influences blood pressure have been reviewed
C331.
We conclude that larger changes in [K'], lead to
more rapid changes in [Na+Ii, which thus can
blunt the apparent effect of increased [K'], on the
Na+-K+ pump rate when flux is measured over a
longer time period. This has sometimes led to
underestimations of the Kilz for K + activation of
the pump. The most important inference of our
study is that changes in plasma K" within the
physiological range significantly affect the cellular
Na+-K+ pump rate, and this effect, in turn, changes
the steady-state [Na+li. This has important physiological consequences, since many secondary active
transport processes depend on the electrochemical
gradient for Na'.
ACKNOWLEDGMENTS
The experiments shown in Fig. 2 and Table 1
were performed in the laboratory of V.O. and E.T.
in the Department of Medicine, National University
Hospital, Singapore, with funding from Research
Project No. RP 850054 and the Hypertension
Laboratory Fund of the National University of
Singapore. The experiments shown in Figs. 1, 3, 4,
and 5 were done in the laboratory of L.N. in the
Department of Pharmacology at the University of
Leicester School of Medicine, with financial support
from the British Heart Foundation. G.W. thanks the
University of Vermont for granting the sabbatical
leave that made this collaboration possible.
G. D. Webb et al.
700
REFERENCES
I. Shaw TI. Potassium movements in washed erythrocytes. J Physiol (London)
1955; 129 464-75.
2. Glynn IM. Sodium and potassium movements in human red cells. J Physiol
(London) 1956; 134: 278-310.
3. Sachs JR, Welt LG. The concentration dependence of active potassium
transport in the human red blood cell. J Clin Invest 1967; 46: 65-76.
4. Hilton PJ, Patrick J. Sodium and potassium flux rates in normal human
leucocytes in an artificial extracellular fluid. Clin Sci 1973; 44.
439-45.
5. Hilton PJ. Cellular sodium transport in essential hypertension. New Engl J Med
1986; 314: 222-9.
6. Levenson R. lsoforms of the Na,K-ATPase: family members in search of
function. Rev Physiol Biochem Pharmacol 1994; IU: 1-45
7. Sahin-Erdemli I, Rashed SM, Songu-Mize E. Rat vascular tissues express all
three a-isoforms of Na+-K+-ATPase. Am J Physiol 1994; 266: H359-3.
8. lnaba M. Maede Y. Na,K-ATPase in dog red cells. J Biol Chem 1986; 261:
16099-105.
9. Gilmore-Hebert M, Schneider JW, Green AL, et al. Expression of multiple
Na+, K +-adenosine triphosphate isoform genes in human hematopoietic cells.
J Clin Invest 1989; 84. 347-51.
10. Hilton PJ, Edmondson RPS, Thomas RD, Patrick J. The effect of external
potassium concentration on leucocyte cation transport in vim.
Clin Sci Mol Med 1975; 49: 385-90.
II. Taylor EA, Ang LM, Oh VMS. Inhibition of lymphocyte sodium pumps by a
low serum concentration of potassium in essential hypertension.
Asia Pacific J Pharmacol 1987; 2 249-54.
12. Haber RS, Pressley TA, Loeb IN, Ismail-Beigi F. Ionic dependence of active
Na-K transport: 'clamping' of cellular Na+ with monensin. Am j Physiol 1987;
253 F2633.
13. Boon NA, Oh VMS, Taylor EA, Johansen T, Aronson JK, Grahame-Smith DG.
Measurement of specific ['Hl-ouabain binding to different types of human
leucocytes. Br J Clin Pharmacol 1984; 18: 153-61.
14. Oh VMS, Taylor EA, Ding JL, Boon NA, Aronson JK, Grahame-Smith DG.
Enhancement of specific ['Hlouabain binding and ouabain sensitive "rubidium
influx in intact human lymphocytes by a dialysable factor in human and fetal
calf serum. Clin Sci 1987; 72 71-9.
15. Clausen T, Everts ME, Kjeldsen K. Quantification of the maximum capacity for
active sodium-potassium transport in rat skeletal muscle. J Physiol 1987; 388:
16MI.
16. Ruef P, Bohler T. Linderkamp 0. Deformability and volume of neonatal and
adult leukocytes. Pediatr Res 1991; 2 9 128-32.
17. Harootunian AT, Kao JPY, Eckert BK, Tsien RY. Fluorescence ratio imaging of
cytosolic free Na' in individual fibroblasts and lymphocytes. J Biol Chem 1989;
264: 1945867.
18. Ang LM. Studies in vitro of sodium/potassium adenosine triphosphatase in
health, pregnancy-induced hypertension, and essential hypertension. PhD
Thesis, National University of Singapore, 1989.
19. Garay RP. Garrahan PJ. The interaction of sodium and potassium with the
sodium pump in red cells. J Physiol 1973; 131: 297-325.
20. Nakao M, Gadsby D. [Na] and [K] dependence of the Na/K pump
current-voltage relationship in guinea pig ventricular myocytes. J Gen Physiol
1989; 94 539-65.
21. Hirsche H, Schumacher E, Hagemann H. Extracellular K + concentration and
K + balance of the gastrmemius muscle of the dog during exercise.
Pnuegers Arch 1980; 387: 231-7.
22. Hnik PH, Krehule I, K r i n J, et al. Work-induced potassium changes in skeletal
muscle and effluent venous blood assessed by liquid ion-exchanger
microelectrodes. Pnuegers Arch 1976; 362: 85-94.
23. McCabe RD, Young DB. Potassium inhibits cultured vascular smooth muscle
cell proliferation. Am J Hypertens 1994; 7: 346-50.
24. Moore EDW, Fay FS. lsoproterenol stimulates rapid extrusion of sodium from
isolated smooth muscle cells. Proc Natl Acad Sci 1993; 90: 805862.
25. Nelson MT. Patlak JB. Worley 111 IF, Standen JB. Calcium channels, potassium
channels, and voltage dependence of arterial smooth muscle tone. Am J Physiol
1990; 259 C3-18.
26. Sigurdsson JA, Bengtsson C. Urinary findings and renal function in
hypertensive and normotensive women. Acta Med Scand 1981; Suppl. 646 51-3.
27. Ueshima H. Tanigaki M, lida M, Shimamoto T. Konishi M, Komachi Y.
Hypertension, salt, and potassium. Lancet 1981: k 504.
28. HDFP Cooperative Group. Baseline laboratory examination characteristics of
the hypertensive participants. Hypertension 1983; 5 IV-I33-59.
29. Rinner MD. Spliet-van Laar L, Kromhout D. Serum sodium, potassium, calcium
and magnesium and blood pressure in a Dutch population. J Hypertens 1989; 7:
977-81.
30. He J. Tell GS, Tang Y-C, Mo P-S, He G-Q. Relation of electrolytes t o blood
pressure in men, the Yi People Study. Hypertension 1991; 17: 373-85.
31. Cappuccio FP. MacGregor GA. Doer potassium supplementation lower blood
pressure?A meta-analysis of published trials. J Hypertens 1991; 9 465-73.
32. Singh RB, Rastogi SS, Singh R, Ghosh S, Niaz MA. Effects of guava intake on
serum total and highdensity lipoprotein cholesterol levels and on systemic
blood pressure. Am J Cardiol 1992; 7 0 1287-91.
33. Blaustein MP. Physiological effects of endogenous ouabain: control of
intracellular Ca2+ stores and cell responsiveness. Am J Physiol 1993; 264:
C I367-87.