Proton efflux from rat skeletal muscle in vivo: changes in hypertension.

1. An analysis of the recovery kinetics of intracellular pH and phosphocreatine concentration after exercise in skeletal muscle was developed to calculate the rate of proton efflux in vivo. 2. Recovery of rat leg muscle pH after sciatic nerve stimulation was faster in spontaneously hypertensive rats than in Wistar-Kyoto controls (both n = 5). 3. Analysis of these data showed that the rate of proton efflux depends on intracellular pH, being greater at lower pH. 4. The early rate of proton efflux was greater in spontaneously hypertensive rats [measured over the first 0.8 min, 12.5 mmol min-1 kg-1 (SEM 1.8) in spontaneously hypertensive rats compared with 7.6 mmol min-1 kg-1 (SEM 0.4) in Wistar-Kyoto rats, P less than 0.05], even though pH at the start of recovery was higher [6.30 (SEM 0.03) in spontaneously hypertensive rats compared with 6.17 (SEM 0.01) in Wistar-Kyoto rats, P less than 0.01]. 5. This novel analysis provides a quantitative estimate of the rate of proton efflux in vivo, and demonstrates directly that this is increased in spontaneously hypertensive rats, as has previously been inferred from pH changes during exercise and studies of cultured muscle cells in vitro.