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

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  • Department of Physiology and Biophysics
  • Department of Sport Science

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 HCO 3 - 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 HCO 3 -. 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 intraand extracellular pH had little effect on K + efflux during contraction. In conclusion, elevated extracellular HCO3 - had no significant effect on muscle fatigue, pH i, and K+ efflux. These findings indicate that alternative mechanisms must be considered for the ergogenic effect of HCO3 - observed in integral exercise studies.

Original languageEnglish
JournalJournal of Applied Physiology
Pages (from-to)494-503
Number of pages10
Publication statusPublished - 1 Aug 2007

    Research areas

  • Muscle fatigue

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