Quantitative
role of the intracellular
bicarbonate
buffer system in response to an acute acid load
S. VASUVATTAKUL,
Renal Division,
L. C. WARNER,
St. Michael’s
Hospital,
AND
University
Vasuvattakul,
S., L. C. Warner, and M. L. Halperin.
Quantitative role of the intracellular bicarbonate buffer system
in response to an acute acid load. Am. J. Physiol. 262 (Regulatory Integrative Comp. Physiol. 31): R305-R309, 1992.-Our
purpose was to quantitate the proportion of H+ removed by the
bicarbonate buffer system (BBS) when a modest load of H+
was infused acutely. In addition, the quantitative impact of
hyperventilation on the BBS in the extracellular fluid (ECF)
and other compartments in this setting was assessed. Three
groups of rats (399 & 3 g) were anesthetized and connected to
a respirator to control their arterial PCO~ and to collect expired
air. Metabolic acidosis (pH 7.26 t 0.01, bicarbonate 18 t 1
mM) was induced by infusion of HCl(O.15 M, 4 mmol/kg) over
60 min, and expired air was collected for two ZO-min periods
beginning 75 and 105 min after the start of the infusion of HCl
in each group. Each rat served as its own control for the rate
of production of CO* from metabolism. The first two groups
were time controls. Their arterial PCO~ was constant at either
ambient (50 mmHg) or hyperventilation levels (30 mmHg)
during both collections (n = 5 each). In the experimental group
(n = 6), the PCO~ was decreased from 40 to 27 mmHg during
the second collection. The rate of production of CO2 from
metabolism did not rise in the second collection in the time
control experiments (change = -13.4 & 1.7 and -1.4 & 2.5
pmol/min, respectively), whereas more COZ was collected during the second period in the experimental group (change = 42
* 9 pmol/min, P = 0.02). In the experimental group, 839 pmol
of the 1600 pmol H+ infused were removed by the BBS in the
ECF at PC02 40 mmHg, this rose to 1,065 pmol when the PCO~
was decreased to 27 mmHg. After hyperventilation, 726 pmol
of H+ ions that were previously bound to nonbicarbonate buffers were removed by the BBS. The BBS outside the ECF
removed 69% of these H+ (equivalent to 500 pmol H+). Thus
hyperventilation could help maintain the net charge and function of intracellular proteins after a modest acid load.
acid-base; buffer capacity; exercise; hyperventilation; lactic acidosis; metabolic acidosis
BUFFERING has been divided into two general categories,
the nonbicarbonate
and the bicarbonate buffer systems
(for review see Refs. 8, 22). For the latter to be effective,
the CO2 produced must be removed from the body by
hyperventilation.
It is well known that metabolic acidosis leads to stimulation of the respiratory centers, resulting in an increase
in alveolar hyperventilation.
Although it is widely held
that this hyperventilation
is critically important for defense of extracellular pH, Madias and co-workers (14)
demonstrated that the expected degree of hypocapnia
may produce a large enough reduction in the concentration of bicarbonate in plasma to lower the pH in plasma
in dogs that had received an infusion of hydrochloric
acid. They called this hyperventilation
maladaptive, implying that it was disadvantageous to the animal.
The purpose of the present study was to obtain quantitative information
on the roles of the extracellular and
intracellular
bicarbonate buffer system after an acute
M. L. HALPERIN
of Toronto, Toronto, Ontario M5B lA6, Canada
acid load. Furthermore,
the role of hyperventilation
in
response to acute metabolic acidosis was evaluated. To
accomplish this goal, acute metabolic acidosis was induced in rats by infusion of 4 mmol/kg of 0.15 N HCl.
The component of buffering by the bicarbonate system
in the extracellular fluid (ECF) was quantitated with and
without hyperventilation.
To document the quantitative
role of the intracellular
(really non-ECF) bicarbonate
buffer system during hyperventilation,
production of CO2
related to metabolism
and titration of nonbicarbonate
buffers was determined.
Results to be reported indicate that approximately half
of the proton load was buffered in the ECF by the
bicarbonate buffer system when 4 mmol HCl/kg body wt
was infused. Hyperventilation
for 20 min resulted in the
removal of an additional 45% of the acid load via the
bicarbonate buffer system. In this case, only 14% of the
extra bicarbonate buffering occurred in the ECF, and
presumably the remainder was primarily
the result of
intracellular
events.
METHODS
Experimental Protocol (Fig. 1)
Studies were carried out on 15 male Wistar rats with body
weights that ranged from 380 to 430 g. Bats were anesthetized
with thiobutabarbital (Inactin; 100 mg/kg body wt ip). After
tracheostomy, tidal volume and frequency of respiration were
adjusted with a rodent respirator (model 683, Harvard Instruments) to maintain the PCO~ of arterial blood in the desired
range. Cannulas were inserted into a femoral vein for infusion
and the femoral artery for sampling. Body temperature was
maintained constant by external heat sources.
Metabolic acidosis was induced by an intravenous infusion
of 0.15 N HCl (4 mmol/kg body wt) for 60 min (67 prnol
min-l . kg body wt-‘). Commencing at 60 min and for the next
15 min, blood was obtained for pH and Pco~. There was little
change in blood pH (0.04 t O.OOS),PCO~ (-1.4 & 0.7 mmHg),
and the concentration of bicarbonate (0.9 & 0.2 mM). Expired
air was then collected for two separate periods in a Douglas
bag and analyzed for volume and COS. In this way, each rat
could serve as its own control for the rate of production of CO2
from metabolism. In every experiment, blood was drawn for
measurements of lactate and anion gap to ensure that other
acid loads were not present.
Time controls. The PCO~ of blood in five rats was adjusted to
30 mmHg, and in five additional rats it was permitted to remain
at 50 mmHg, the value at rest in these anesthetized rats. At
the 75-min time point, blood was taken and expired air collected
for 10 (rats with PCO~ 50 mmHg) or 20 min (rats with PCO~ 30
mmHg) with bracketing samples of blood. Commencing at 105
min, another 20-min collection of expired air was obtained with
bracketing samples of blood, while the PCO~ in arterial blood
was maintained constant.
Effect of hyperuentilution. Five rats were studied in this
group. The protocol was identical to the time controls with the
0363-6119/92 $2.00 Copyright 0 1992 the American Physiological
Society
R305
R306
INTRACELLULAR
exception that the PCO~of blood was adjusted to -40 mmHg
after anesthesia;all collections of CO:!were for 20 min (Fig. 1).
The first collection was obtained at 75 min, and the PCO*was
close to 40 mmHg at the start and end of this period. The
secondcollection beganat 105 min and had an initial PCO*in
arterial blood of 40 mmHg. Hyperventilation occurred from
this point, and the final PCO~in blood was 27 mmHg at 125
min.
Analytic
Methods
BUFFERS
bolic COz.The acid-baseCO* (pmol/min) wascalculatedas the
total COz producedwith hyperventilation minus the metabolic
CO, in the preceding 20 min.
Nonbicarbonate
buffering. A maximum estimateof this buffering was calculated as the total load of H+ infused minus the
fall in bicarbonate (the latter term was equal to the fall in
bicarbonate in the ECF without hyperventilation plus the acidbaseCO:!produced during hyperventilation).
Anion gap. This was calculated as the sum of the measured
cations (Na’ + K’) minus the sumof the measuredanions(Cl+ HCO;).
The pH and PCO~in blood were measuredwith a blood gas
analyzer (model 178,Corning). The concentration of bicarbonate in plasmawascalculated using pK’ of 6.10 and a solubility Statistical Analysis
factor of 0.0301 (13, 24). The concentrations of Na, K, Cl,
Data are expressedas meansf SE. Statistical analysiswas
lactate, and glucosewere measuredaspreviously described(loperformed using the Student’s t test. P < 0.05 was considered
12). The volume of expired air was measureddirectly, and the statistically significant.
concentration of CO* wasdetermined by a medical gasanalyzer
(Beckman LB-2).
RESULTS
Calculations
(See APPENDIX for Examples)
The values for acid-base and electrolytes in plasma of
rats after the infusion of HCl with and without hyperof body weight (3)] and the percent attributed to the ECF ventilation
are reported in Table 1:Infusion
of HCl led
[derived from inulin or sulfate spacesor 33% of body water (7, to the production
of metabolic acidosis with a fall in
17)] were usedfor calculation of the initial volume of ECF in bicarbonate
from 28 f 1 to 18 + 1 mM. As expected,
rats in this weight range.
there was a rise in the concentration
of K in plasma of
Volume of ECF after infusion of HCL. The volume of ECF <l mM from the control value of 4.0 & 0.2 mM (15).
was calculated using the chloride space (23). The input of Cl
equaledthe quantity infused, and the output wasequal to blood Other significant findings were a fall in the concentration
of Na (from 149 f 1 mM) owing to the infusion of a Nasamplingbecauselittle urine wasproduced in this interval.
free
solution but a rise in Cl (from 107 + 1 mM) due to
Content of bicarbonate in ECF. This content was the product
of the concentration of bicarbonate in plasma and the volume the infusion of HCl. Of note, there was no significant
of ECF. For interstitial fluid, a correction wasmadefor Donnan change in anion gap or lactate; values before infusion
effects taking into consideration the molality vs. molarity of were 14 k 2 meq/l and 0.7 + 0.1 mM, respectively. The
the solutions.
hematocrit fell somewhat after infusion of HCl (from 47
Distribution
of infused H’. H+ that remained outside the f 0.7 to 45 f 0.7 in the group without hyperventilation
ECF equaledthe difference betweenthe number of micromoles and from 45 + 1.2 to 43 f 1.0 in the group that had the
of H’ infused and the decreasein content of bicarbonate in the fall in Pcos); these changes were not statistically
signifECF (alsoin rmol).
icant.
Hyperventilation
led
to
a
significant
fall
in
PCO~
Metabolic CO,. The quantity of CO2produced during metaband
rise
in
pH
with
a
small
additional
decline
in
the
olism (pmol/min) wascalculated from the total quantity of CO,
of bicarbonate.
exhaled over 10 or 20 min. The number of micromoles was concentration
To validate the procedure and experimental conditions
calculated using a molar volume for CO2 of 22.26 liters at
standard temperature and pressure(21) and expressedas mi- to collect COz, all the expired air was collected for a locromolesper minute.
and then a 20-min period in five rats at constant ambient
Volume of ECF. Standard values for total body water [67%
Acid-base CO,. The quantity of CO, releasedduring hyperventilation representedmetabolic plus acid-baseCO*. The total
production of CO2was calculated as describedabove for metaRespirator
0.15 M HC14 mmolikg
KG
Q
.
Pcop
(50 mmHg). The rate of production of COs fell
slightly in the second period
pmol/min,
change = -13.4 +
step was to evaluate the rate
consecutive 20-min periods in
(250 f 20 and 230 + 20
1.7 pmol/min).
The next
of production of CO9 in
rats at levels of PCO~that
Table 1. Values in blood before
and after hyperventilation
60
126
75
Period
so
so
30
30
40
4Qto30
Fig. 1. Protocol of study. Fifteen rats (399 + 3 g) were anesthetized
and connected to a respirator to select Pcoz of arterial blood. Metabolic
acidosis was induced by infusion of 0.15 N HCl (4 mmol/kg) over 60
min. Expired air was collected over 10 or 20 min. First collection began
at 75 min and second collection at 105 min after start of infusion of
HCI.
Period
2
7.37+0.01t
27*1*t
16*l*t
139*1*
5.0+0.2*
7.26+0.01*
4021
mmHg
18+1*
HCOJ, mM
Na, mM
141+1*
4.83~0.2;
K, mM
Cl, mM
117f2*
117*1*
13il
1321
Anion gap, meq/l
Lactate, mM
0.7LtO.l
0.8rtO.l
Values are means + SE, n = 5 rats. HCl was infused as described in
METHODS.
Values after this infusion are shown where PCol was adjusted to 40 (Period 1) and 27 mmHg (Period 2). * P C 0.05 for effect
of infusion of acid. t P < 0.05 for effect of hyperventilation.
PH
Pco2
I
I&O,,
INTRACELLULAR
R307
BUFFERS
reflected conditions during hyperventilation
(30 mmHg).
The rates of production of CO2 in the first and second
collections did not differ significantly
(210 t 20 and 210
k 20 pmol/min,
change = -1.4 t 2.5 pmol/min;
Fig. 2).
When the PCO~ was maintained
at ambient levels (50
mmHg) in the first and second collections, the concentration of bicarbonate was not significantly
different
during the first (19.5 & 1.1 vs. 19.5 t 1.2 mM) or second
collection (19.6 & 1.2 vs. 19.9 t 1.1 mM). Similar observations were made at PCO~ of 30 mmHg (first collection
17.1 & 1.2 vs. 17.6 & 1.4 mM, second collection 16.8 t
1.4 vs. 16.4 & 1.3 mM). This production of CO2 is called
metabolic COO.
Effect
of
150
Hyperventilation
b
The rate of production of COs was increased significantly (42 & 9 pmol/min)
in paired observations during
hyperventilation
(187 k 9 to 229 k 9 pmol/min,
P =
0.02; Fig. 3). The concentrations of bicarbonate declined
significantly during hyperventilation
(18.0 & 0.8 to 15.7
* 1.1, P = 0.01; Table 1).
Using the methods of calculation
described in the
APPENDIX, just over half the buffering without hyperventilation was via the bicarbonate buffer system of the
ECF, When hyperventilation
occurred, this ECF buffering could account for 67% of the original acid load. Of
interest, the majority of the buffering in the non-ECF
compartment was via a bicarbonate buffer system (Table
2) .
DISCUSSION
The principal findings in this study were that the
bicarbonate buffer system removes (buffers) most of the
H+ load (98%) when this load is modest in degree and
that hyperventilation
occurs (Table 2; see APPENDIX).
The bicarbonate buffer system outside the ECF is quantitatively important (31% of total), but only if hyperven-
z
8
I
8
8
f
I
200
8 (II
1
150
!
0.........................-0
0 ----.....0 ----------0...............
----....-H
I
First
---9..
8
I
4
Second
Fig. 2. Rate of production of CO2 in first and second collections with
constant Pco~. For details, see METHODS.
l , Rats with PCO* of 50
mmHg, o rats with Pcoz of 30 mmHg. Mean values for Pcoz 50 mmHg
were 250 k 20 and 230 k 20 pmol/min in first and second periods,
respectively. Corresponding values for PCO~ 30 mmHg were 210 rt 20
and 210 k 20 pmol/min, respectively.
!
I
.
4
t
First
Second
Fig. 3. Rate of production of COz with hyperventilation. For details,
see Fig. 2 legend. PCO~ of arterial blood was 40 mmHg during fmt
collection and fell from 40 to 30 mmHg in second collection. Rise in
production of CO* was statistically significant (P = 0.02)
Table
2. Proportion
Location
of buffering of the H+ load
of Buffer
Hyperventilation
No
Yea
Extracellular fluid
Bicarbonate
839
1,065
Intracellular fluid
Nonbicarbonate
761’
35
Bicarbonate
500
Results are reported in pmol H+ removed by bicarbonate with and
without hyperventilation after a modest infusion of HCl (1,660 pmol).
* Total buffering outside extracellular fluid is 761 pmol; most of this
buffering seems to be due to nonbicarbonate vs. bicarbonate buffer
system because there is a considerable backtitration of these buffers
after hyperventilation occurred.
tilation occurs. In the following paragraphs, we shall
provide background information concerning the effect of
hyperventilation
on the bicarbonate buffer system.
The quantitative
information
provided in this study is
somewhat different from that in the literature (22) in
that a larger percent of the acid load was buffered by the
bicarbonate buffer system in our experiments. This probably reflects the fact that the load of HCl infused was
smaller in our experiments
(4 mmol/kg)
than in the
experiment of Swan and Pitts (22) (10 mmol/kg);
it is
well known that, when the load of acid rises progressively, much less of the added protons is buffered by the
bicarbonate vs. nonbicarbonate
buffer systems (8). Another difference in the design of our experiments compared with those of previous investigators (22) is that we
attempted to examine the nature of the intracellular
buffering (i.e., bicarbonate vs. nonbicarbonate
buffers,
with and without hyperventilation).
The effect of hyperventilation
on the bicarbonate
buffer system is to lower, primarily, the concentration of
either H+ or bicarbonate, depending on the quantity of
nonbicarbonate buffers in a given compartment.
In more
detail, in the absence of nonbicarbonate buffers, lowering
the PCO~ by half will lead to a halving of the concentration of H+ with almost no change in the concentration
of bicarbonate because the concentration of bicarbonate
R308
INTRACELLULAR
exceeds that of H+ by almost 106-fold whereas they react
with a 1:l stoichiometry
(Fig. 4). In contrast, in the
presence of a very large quantity of nonbicarbonate buffers, the initial fall in the concentration
of H+ leads to
backtitration
of the enormous quantity of nonbicarbonate buffers with the subsequent consumption of bicarbonate (Fig. 4). In a system with an infinite supply of
these nonbicarbonate buffers, this fall in PCO~ will lead
to a halving (almost) of the concentration of bicarbonate
with little fall in the concentration of H+ (Fig. 4). As an
approximation,
the low quantity of nonbicarbonate buffers reflects events in the ECF, and a high quantity of
these buffers reflects events in the intracellular
fluid
(ICF). Furthermore,
hyperventilation
should lead initially to a larger concentration
gradient for H+ across
the cell membrane, lower in the ECF. Therefore the
relative contribution of ICF and ECF bicarbonate buffers
depends not only on the relative quantity of nonbicarbonate buffers but also on the net movement of H+ as
influenced by the magnitude of the H+ concentration
gradient across the plasma membrane and the systems
that translocate protons or bicarbonate
across the
plasma membrane.
One can ignore the contribution of the nonbicarbonate
buffers of the ECF because only a small quantity of these
buffers are present in the ECF. With an acute acid load,
H’ ions are buffered by bone, consuming sodium bicarbonate in the process (4, 5); very little buffering occurs
with calcium salts in this time interval (no accumulation
or excretion of Ca2+). Therefore less than half of the load
of H+ given was buffered by nonbicarbonate
and bicarbonate buffers of the ICF (Table 2). This is consistent
with a relatively small change in pH of the ICE‘ (compared with the ECF) (1,9, 19).
When hyperventilation
was induced, there was a small
further fall in the concentration
of bicarbonate in the
ECF. Calculations revealed that almost two-thirds of the
total load of H+ was now removed by the bicarbonate
buffer system of the ECF (Table 2). For bicarbonate to
be consumed, there must be the production of organic
acids or the transfer of H+ from nonbicarbonate
buffers
induced by a fall in the concentration of H+ in their local
environment
due to hyperventilation
(Fig. 4). Because
+
k1 +
HCOj
B
-
I$0 + co, t
0
HB
Fig. 4. Effects of hyperventilation on bicarbonate buffer system. Top
line is intended to represent events in extracellular fluid, a compartment with only a minor contribution of nonbicarbonate buffers. In
extracellular fluid, main effect of hyperventilation is to lower concentration of H’. In contrast, entire figure is intended to represent events
in ICF with hvnerventilation: there is a small fall in H’ concentration
that leads to backtitration of large content of nonbicarbonate buffers
and subsequent consumption of bicarbonate and production of nonprotonated intracellular proteins (B”). Thus the major effect of hyperventilation here is to lower the concentration of bicarbonate.
BUFFERS
there was no appreciable accumulation of the conjugate
base of organic acids in plasma (the concentration
of
lactate and the anion gap did not rise; Table l), backtitration of nonbicarbonate
buffers is the most likely
source for these protons (hyperventilation
should lower
the concentration of H+ in the ICF somewhat). Quantitatively, two-thirds of the CO2 produced as a result of
lowering the Pco2 from 40 to 27 mmHg was derived from
sources other than the ECF, presumably the ICF. This,
in effect, means that H+ ions were released from nonbicarbonate buffers, which led to the consumption of bicarbonate, primarily
in the ICF. This process should
maintain intracellular
proteins (nonbicarbonate
buffers)
with close to their normal net charge (and function) (18).
The increased utilization
of the bicarbonate buffer
system and the resultant sparing of the nonbicarbonate
buffers may be important in the physiology of exercise.
Skeletal muscle must buffer an enormous load of H+
when vigorous exercise is performed where the supply of
oxygen is less than demand for metabolism (6, 16, 20).
To remove a significant quantity of these H+ ions without
them binding to intracellular
proteins, the H+ formed
during anaerobic glycolysis must combine with bicarbonate (producing carbonic acid, which itself must be removed). To remove more than the usual quantity of Con,
hyperventilation
must occur. The timing of this hyperventilation
is crucial. It must occur largely, if not exclusively, before the race because the supply of blood to
muscle will not increase sufficiently in the few seconds
of the sprint to achieve this removal. Thus backtitration
of intracellular nonbicarbonate buffers (proteins) creates
extra “parking spots” for H+ produced with lactate during
the bout of maximal and relatively anaerobic exercise
without obliging such a drastic fall in pH of the ICF in
skeletal muscle.
To summarize, it appears that close to half of the H+
ions are buffered by the bicarbonate buffer system of the
ECF with an acute but modest load of HCl. In the
absence of hyperventilation,
the remaining H+ ions are
buffered by nonbicarbonate
buffers. With the appropriate degree of hyperventilation,
backtitration
of nonbicarbonate buffers occurs leading to consumption of more
bicarbonate, primarily of non-ECF origin. This sequence
of events prevents the titration of nonbicarbonate buffers
and may enhance function of intracellular
proteins with
a modest degree of acidosis.
APPENDIX
Sample Cald5tion.s
ECF volume. Initial value is 33% of body water (7,17). Total
body water is 67% of body weight (67% X 400 g X 33% = 89.3
ml) (3). The plasmavolume is 31.3 ml/kg body wt (12.5 ml)
(‘2). The interstitial
fluid volume is the difference betweenECF
and plasmavolumes (89.3 - 12.5 = 76.8 ml). The ECF volume
after infusion of HCl was calculated from the chloride space
(23) and was94.2ml; the chloride extracted during the multiple
blood samplingswastaken into account, and a total of 2 ml of
blood was withdrawn. Plasma and interstitial volumes were
calculated as describedabove.
Quantity of bicarbonate. Before infusion, the content of bicarbonate in plasmawas the product of the concentration of
bicarbonateand the plasmavolume. The content of bicarbonate
INTRACELLULAR
determination of bone surface elements: effects of reduced medium
pH. Am. J. Physiol. 250 (Renal Fluid Electrolyte Physiol. 19):
F1090-Fl097,1986.
Cheetham,
M., L. Boobis,
S. Brooks,
and C. Williams.
Human
muscle metabolism during sprint running. J. Appl. Physiol. 61: 5460, 1986.
Edelman,
I., and J. Leibman.
Anatomy of body water and
electrolytes. Am. J. Med. 27: 256-277, 1959.
Fernandez,
P., R. Cohen,
and G. Feldman.
The concept of
bicarbonate distribution space: the crucial role of body buffers.
Kidney Int. 36: 747-752,1989.
in the interstitial fluid isthe product of 1.05 x the concentration
of bicarbonate in plasmaand the interstitial fluid volume
Before = (28 X 12.5) + (28 X 1.05 X 76.8) = 2,608 pmol
After = (18 X 13.2) + (18 X 1.05 X 81)
= 1,769 pmol
The decreasein content of bicarbonate equalsthe quantity
of H’ buffered in the ECF. This value was comparedwith the
quantity of HCl infused (1,600 pmol).
The additional quantity of H’ removed by the bicarbonate
buffer system after hyperventilation was 726 pmol (Fig. 3, 42
pmol/min X 20 min of acid-baseCOz or 840 pmol - 114 pmol
of preformed COS).
The total amount of preformed COz was 1.2 mM at Pcoz 40
mmHg and 0.8 mM at PCO~ 27 mmHg (24). If all this CO* was
distributed in total body water after the HCl infusion (285 ml),
114 pmol of COz would have been collected in the period of
hyperventilation. Thus backtitration of nonbicarbonate buffers
would be 726 instead of 840 pmol.
The proportion of buffering by bicarbonate after hyperventilation wascalculatedasthe decreasein content of bicarbonate
in the ECF before hyperventilation plus 726 pmol of acid-base
CO2 due to backtitration of nonbicarbonate buffers due to
hyperventilation (seeTable 2).
The componentof this additional bicarbonate buffering after
hyperventilation that was attributable to the ECF was calculated using the new bicarbonate concentration of 15.7 mM as
describedin Quantity of bicurbonute.In this case,an extra 226
pmol of bicarbonatewas consumedin the ECF. This leaves500
pmol of bicarbonate (726 - 226 pmol) to be buffered by bicarbonate outside the ECF.
To titrate all these extra 726 pmol of bicarbonate, a source
of H+ was needed. Given the absenceof a rise in lactate or
anion gap (expected would be 726 pmol/285 ml or closeto 2.5
meq/l with a distribution volume of total body water), it seems
that mostof the H+ were derived from backtitration of virtually
all the nonbicarbonate buffers that were involved in buffering
of the initial load of HCl without hyperventilation.
Address for reprint requests: M. L. Halperin, St. Michael’s Hospital,
Lab #l, Research Wing, 38 Shuter St., Toronto, Ontario M5B lA6,
Canada.
Received 17 May 1991; accepted in final form 11 September 1991.
REFERENCES
1. Aickin,
C., and R. Thomas.
Micro-electrode measurement of
intracellular pH and buffer power of mouse soleus muscle fibers.
Am. J. PhysioL 267: 791-810,1977.
2. Altman,
P. L., and D. S. Dittmer.
Blood and other body fluids.
In: SioZogical Handbook, edited by P. L. Altman and D. S. Dittmer.
Washington, DC: Fed. Am. Sot. Exp. Biol., 1961, p. 359.
3. Altman,
P. L., and D. S. Dittmer.
Total body water: mammals
other than man. In: The SiorOgy Data Book (2nd ed.), edited by P.
L. Altman and D. S. Dittmer. Bethesda, MD: Fed. Am. Sot. Exp.
Biol., 1974, p. 1990-1992.
4. Bettice,
J. A., and J. L. Gamble.
Skeletal buffering of acute
metabolic acidosis. Am. J. Physiol. 229: 1618-1624, 1975.
5. Bushinskv.
D.. R. Levi-Setti.
and F. Coo. Ion micronrobe
R309
BUFFERS
Gamble,
J.,
Jr.,
P. Zuromskis,
J. Bettice,
and
R. Ginsberg.
Intracellular buffering in the dog at varying CO:! tensions. Clin.
Sci. Lond. 42: 311-324, 1972.
I., and A. W. Wahlefeld.
L+ Lactate determination
lo* Gutmann,
with lactate dehydrogenase and NAD. In: Methods of Enzymatic
Analysis, edited by H. U. Bergmeyer. New York: Academic, 1974,
p. 1464-1468.
11
’
Halperin,
Jungas.
M.,
P. Vinay,
A.
Gougoux,
C. Pichette,
and
R.
Regulation of the maximum rate of renal ammoniagenesis
in the acidotic dog. Am. J. Physiol. 248 (Renal Fluid Electrolyte
Physiol. 17): F607-F615, 1985.
12. Halperin,
M. L., M.
Stinebaugh.
B. Goldstein,
A. Haig,
M.
D. Johnson,
Studies on the pathogenesis of type I
(distal) renal tubular acidosis as revealed by the urinary PCO~
tensions. J. Clin. Invest. 53: 669-677, 1974.
Hastings,
A. B., and J. Sendroy,
Jr. The effect of variation in
13- ionic strength on the apparent first and second dissociation constants of carbonic acid. J. Biol. Chem. 65: 445-455, 1925.
14 Madias,
N., W. Schwartz,
and J. Cohen.
The maladaptive
’ renal response to secondary hypocapnia during chronic HCl acidosis in the dog. J. Clin. Invest. 60: 1393-1401, 1977.
and
B. J.
15. Magner,
P. O., L. Robinson,
L. Halperin.
The plasma
E. M.
Halperin,
R. Zettle,
and
potassium concentration in metabolic acidosis: a re-evaluation. Am. J. Kidney Dis. 11: 220-224,
16 1988.
Medbo,
J. I., and 0. M. Sejersted.
Acid-base and electrolyte
’ balance after exhausting exercise in endurance-trained and sprinttrained subjects. Acta Physiol. Stand. 125: 97-109, 1985.
17. Oh, M., and H. Carroll.
Regulation of extra- and intracellular
fluid composition and content. In: Fluid Electrolyte and Acid-Base
Disorders, edited by A. Arieff and R. Defronzo. New York: Churchill Livingstone, 1985, vol. 1, p. l-38.
18. Rahn, H. Acid-base balance and the “milieu interieur.” In: Claude
Bernard and the Internal Environment. A Memorial Symposium,
1g edited by E. D. Robin. New York: Dekker, 1979, p. 179-190.
. ROOS, A., and W. Boron.
Intracellular pH. Physiol. Rev. 61: 296
434,198l.
20. Sahlin,
K., R. Harris,
and E. Hultman.
Creatine kinase equilibrium and lactate content compared with muscle pH in tissue
samples obtained after isometric exercise. Biochem. J. 152: 173180,1975.
21. Shedlovsky,
T., and D. Mac Innes.
The 1st ionization content
of carbonic acid, O-38”, from conductance measurements. J. Am.
Chem. Sot. 57: 1705-1710,1935.
22. Swan, R. C., and R. F. Pitts. Neutralization of infused acid by
nephrectomized dogs. J. Clin. Invest. 34: 205-212, 1955.
R. L., H. L. Bleich,
and W. B. Schwartz.
The renal
23. Tannen,
response to acid loads in metabolic alkalosis; an assessment of the
mechanisms regulating acid excretion. J. Clin. Invest. 45: 562-572,
1966.
24. Van Slyke,
D. D., J. Sendroy,
A. B. Hastings,
and J. M.
Neill.
Studies of gas and electrolyte equilibria in blood. X. The
solubility of carbon dioxide at 38°C in water, salt solution, serum
and blood cells. J. Biol. Chem. 78: 765-799. 1928.
M.