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Alkalosis increases muscle K + release, but lowers plasma [K + ] and delays fatigue during dynamic forearm exercise
Author(s) -
Sostaric Simon M.,
Skinner Sandford L.,
Brown Malcolm J.,
Sangkabutra Termboon,
Medved Ivan,
Medley Tanya,
Selig Steve E.,
Fairweather Ian,
Rutar Danny,
McKenna Michael J.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.094615
Subject(s) - alkalosis , medicine , chemistry , endocrinology , acid–base homeostasis , venous blood , acidosis , muscle fatigue , electromyography , psychiatry
Alkalosis enhances human exercise performance, and reduces K + loss in contracting rat muscle. We investigated alkalosis effects on K + regulation, ionic regulation and fatigue during intense exercise in nine untrained volunteers. Concentric finger flexions were conducted at 75% peak work rate (∼3 W) until fatigue, under alkalosis (Alk, NaHCO 3 , 0.3 g kg −1 ) and control (Con, CaCO 3 ) conditions, 1 month apart in a randomised, double‐blind, crossover design. Deep antecubital venous (v) and radial arterial (a) blood was drawn at rest, during exercise and recovery, to determine arterio‐venous differences for electrolytes, fluid shifts, acid–base and gas exchange. Finger flexion exercise barely perturbed arterial plasma ions and acid–base status, but induced marked arterio‐venous changes. Alk elevated [HCO 3 − ] and P CO 2, and lowered [H + ] ( P < 0.05). Time to fatigue increased substantially during Alk (25 ± 8%, P < 0.05), whilst both [K + ] a and [K + ] v were reduced ( P < 0.01) and [K + ] a‐v during exercise tended to be greater ( P = 0.056, n = 8). Muscle K + efflux at fatigue was greater in Alk (21.2 ± 7.6 µmol min −1 , 32 ± 7%, P < 0.05, n = 6), but peak K + uptake rate was elevated during recovery (15 ± 7%, P < 0.05) suggesting increased muscle Na + ,K + ‐ATPase activity. Alk induced greater [Na + ] a , [Cl − ] v , muscle Cl − influx and muscle lactate concentration ([Lac − ]) efflux during exercise and recovery ( P < 0.05). The lower circulating [K + ] and greater muscle K + uptake, Na + delivery and Cl − uptake with Alk, are all consistent with preservation of membrane excitability during exercise. This suggests that lesser exercise‐induced membrane depolarization may be an important mechanism underlying enhanced exercise performance with Alk. Thus Alk was associated with improved regulation of K + , Na + , Cl − and Lac − .