Valkina O N, Vergun O V, Turovetsky V B, Khodorov B I
Ulyanovsk State Pedagogical University, Ulyanovsk, Russian Federation.
FEBS Lett. 1995 Mar 20;361(2-3):145-8. doi: 10.1016/0014-5793(95)00143-w.
Frog sciatic nerve and its thin bundles were loaded with fluorescein diacetate in order to monitor changes in cytoplasmic pH (pHi) caused by high K+ depolarization. Isosmotic substitution of external Na+ by K+ at pHo 7.3 led to a steady concentration-dependent (20-120 mM K+) decrease in pHi. Elevation of pHo from 7.3 to 8.5 prevented or even reversed these pHi changes, indicating their strong dependence on transmembrane H+ fluxes. The depolarization-induced intracellular acidification could not be prevented or decreased by any of the following treatments: removal of external Ca2+; application of the Ca2+ antagonists Ni2+ and Co2+; blockade of K+ channels by TEA; addition to the external solution of Zn2+, a blocker of putative voltage-sensitive H+ channels. By contrast, blockade of Na+ channels by 1-3 microM TTX prevented the effect of high K+ concentrations on pHi. It is concluded that the decrease in pHi induced by a prolonged membrane depolarization in frog nerve fibers is mainly due to an enhanced H+ influx through non-inactivating Na+ channels.
