Changes of cytoplasmic pH in frog nerve fibers during K(+)-induced membrane depolarization.
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.
Valkina
O N
ON
Ulyanovsk State Pedagogical University, Ulyanovsk, Russian Federation.
Vergun
O V
OV
Turovetsky
V B
VB
Khodorov
B I
BI
D000818:Animals; D003593:Cytoplasm / Q000502:physiology; D004558:Electric Stimulation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009412:Nerve Fibers / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D026902:Potassium Channel Blockers; D011895:Rana ridibunda; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors
D026902:Potassium Channel Blockers; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D012964:Sodium; D011188:Potassium