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Division of Respiratory and Critical Care Physiology and Medicine, Harbor-UCLA Medical Center, Torrance, California 90509
Received 31 July 1996; accepted in final form 26 March 1997.
Wasserman, Karlman, William W. Stringer, Richard Casaburi,
and Yong-Yu Zhang. Mechanism of the exercise
hyperkalemia: an alternate hypothesis. J. Appl.
Physiol. 83(2): 631-643, 1997.
A progressive
hyperkalemia is observed as exercise intensity increases. The current
most popular hypothesis for the hyperkalemia is that the
Na+-K+
pump cannot keep pace with the K+
efflux from muscle during the depolarization-repolarization process of
the sarcolemmal membrane during muscle contraction. In this report, we
present data that suggest an alternate hypothesis to those previously
described. Because phosphocreatine (PCr) is a highly dissociated acid
and creatine is neutral at cell pH, the concentration of nondiffusible
anions decreases, and an alkaline reaction takes place when PCr
hydrolyzes. This creates a state of cation
(K+) excess and
H+ depletion in the cell. To
examine the balance of K+ and
H+ for exercising muscle during
the early period of exercise when PCr changes most rapidly, catheters
were inserted into the brachial artery and femoral vein (FV) in five
healthy subjects who performed two 6-min cycle ergometer exercise tests
at 40 and 85% of peak oxygen uptake. FV blood was sampled every 5 s
during the first 2 min, then every 30 s for the remaining 4 min of
exercise and the first 3 min of recovery, and then less frequently for
the next 12 min. Arterial sampling was every 30 s during exercise and
simultaneous with FV sampling during recovery. Arterial
K+ concentration
([K+]) increase lagged
FV [K+]
increase. The hyperkalemia observed during early exercise
results from K+ release from
skeletal muscle. FV
[K+] increased by 5 s
of the start of exercise and followed the rate of
H+ loss from the FV blood for the
first 30 s of exercise. FV lactate and
Na+ kinetics differed from
K+ kinetics during exercise and
recovery. As predicted from the PCr hydrolysis reaction, the exercising
limb took up H+ and released
K+ at the start of exercise (first
30 s) at both exercise intensities, resulting in a FV metabolic
alkalosis. K+ release was
essentially complete by 3 min, the time at which oxygen uptake (and,
presumably, PCr) reached its asymptote. These findings lead us to
hypothesize that the early K+
release by the cell takes place with
H+ exchange and that the major
mechanism for the exercise hyperkalemia is the reduction in
nondiffusible intracellular anions in the myocyte as PCr hydrolyzes.
phosphocreatine; acid-base balance; hydrogen ion transport; lactate; potassium
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