Effects of extracellular HCO3− on fatigue, pHi, and K+ efflux in rat skeletal muscles

Author:

Broch-Lips Martin,Overgaard Kristian,Praetorius Helle A.,Nielsen Ole Bækgaard

Abstract

Elevated plasma HCO3 can improve exercise endurance in humans. This effect has been related to attenuation of the work-induced reduction in muscle pH, which is suggested to improve performance via at least two mechanisms: 1) less inhibition of muscle enzymes and 2) reduced opening of muscle KATP channels with less ensuing reduction in excitability. Aiming at determining whether the ergogenic effect of HCO3 is related to effects on muscles, we examined the effect of elevating extracellular HCO3 from 25 to 40 mM (pH from 7.4 to 7.6) on fatigue, intracellular pH (pHi), and K+ efflux in isolated rat skeletal muscles contracting isometrically. Fatigue induced by 30-Hz stimulation at 30 and 37°C was similar between soleus muscles incubated in high and normal HCO3 concentrations. In extensor digitorum longus muscles stimulated at 60 Hz, elevated HCO3 did not affect fatigue at 30°C. In soleus muscles, 30-Hz stimulation induced a ∼0.2 unit reduction in pHi, as determined by using the pH-sensitive probe 2′,7′-bis(2-carboxyethyl)-5( 6 )-carboxyfluorescein. This reduction in pHi was not affected by elevated HCO3. Estimation of K+ efflux using 86Rb+ showed that elevated HCO3 did not affect K+ efflux at rest or during contractions. Similarly, other modifications of the intra- and extracellular pH had little effect on K+ efflux during contraction. In conclusion, elevated extracellular HCO3 had no significant effect on muscle fatigue, pHi, and K+ efflux. These findings indicate that alternative mechanisms must be considered for the ergogenic effect of HCO3 observed in integral exercise studies.

Publisher

American Physiological Society

Subject

Physiology (medical),Physiology

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