title: Alkalosis increases muscle K+ release, but lowers plasma [K+] and delays fatigue during dynamic forearm exercise.
abstract: 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, NaHCO3, 0.3 g kg(-1)) and control (Con, CaCO3) 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 [HCO3-] and PCO2, 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 micromol 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-.
authors.affiliation: Muscle, Ions and Exercise Group, Centre for Ageing, Rehabilitation, Exercise and Sport, School of Human Movement, Recreation and Performance, Victoria University, Melbourne, Victoria, Australia.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Sostaric
authors.forename: Sandford L
authors.initials: SL
authors.lastname: Skinner
authors.forename: Malcolm J
authors.initials: MJ
authors.lastname: Brown
authors.forename: Termboon
authors.initials: T
authors.lastname: Sangkabutra
authors.forename: Ivan
authors.initials: I
authors.lastname: Medved
authors.forename: Tanya
authors.initials: T
authors.lastname: Medley
authors.forename: Steve E
authors.initials: SE
authors.lastname: Selig
authors.forename: Ian
authors.initials: I
authors.lastname: Fairweather
authors.forename: Danny
authors.initials: D
authors.lastname: Rutar
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKenna
mesh_terms: D000471:Alkalosis / Q000097:blood / Q000503:physiopathology*; D002712:Chlorides / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D005542:Forearm; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood; D013997:Time Factors
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium