Effect of calcium and other divalent cations on intracellular pH regulation of frog skeletal muscle

Abstract

1. We examined, in frog semitendinosus muscle, the effect of calcium release, induced by depolarization or caffeine, on intracellular pH (pHi) recovery from an acid load applied at least 40 min later. We also studied the effect of external Ca and other divalent cations on recovery. We used pH-sensitive micro-electrodes; the external pH (pHo) was always 7.35. 2. In fibres depolarized by 50 mM-K, constant [K] X [Cl] in the presence of 1 mM-tetracaine (which blocks Ca release), the rate of pHi recovery from 5% CO2-induced acidification was 0.15 +/- 0.02 delta pHi h-1 (n = 7), whereas in depolarized fibres that had never been exposed to the drug, the rate of recovery was 0.27 +/- 0.01 delta pHi h-1 (n = 5). Yet, when Ca release was not blocked and the depolarized fibres were exposed to tetracaine shortly before CO2 exposure, a similar slow rate of 0.14 +/- 0.03 delta pHi h-1 (n = 7) was observed. When Ca release was blocked by tetracaine, but the drug washed out before recovery, the rate was again 0.27 +/- 0.02 delta pHi h-1 (n = 6). 3. In fibres first depolarized to about -23 mV in 50 mM-K, constant [K] X [Cl] (recovery of 0.23 +/- 0.03 delta pHi h-1, n = 6), and then repolarized to -79 mV in 2.5 mM-K, the slow rate of recovery was the same (0.03 +/- 0.02 delta pHi h-1) as that in fibres without a history of depolarization and thus of Ca release. 4. In fibres depolarized to -50 mV (15 mM-K, constant Cl) and then exposed to caffeine (4 mM) which releases Ca from intracellular stores, the recovery was the same (0.07 +/- 0.03 delta pHi h-1, n = 5) as in depolarized fibres not exposed to caffeine (0.09 +/- 0.01 delta pHi h-1, n = 5). 5. We conclude that in frog muscle transient Ca release induced by either depolarization or caffeine does not affect the rate of subsequent pHi recovery. Tetracaine reversibly inhibits pHi recovery, but this inhibition is not due to its blocking of Ca release. 6. Recovery from CO2-induced acidification of fibres depolarized to -21 mV in 50 mM-K, constant Cl was halved, from 0.31 +/- 0.04 delta pHi h-1 (n = 10) to 0.15 +/- 0.01 delta pHi h-1 (n = 13), when external Ca was raised from 4 to 10 mM.(ABSTRACT TRUNCATED AT 400 WORDS)