Voltage‐dependent intracellular pH in Helix aspersa neurones.

Abstract

1. The intracellular pH (pHi) of large nerve cells from the mollusc, Helix aspersa, was measured with pH‐sensitive micro‐electrodes. Cells were held under voltage clamp and the effect on pHi of different holding potentials was determined. 2. Depolarization of the cell from the resting potential (about ‐50 mV) to ‐10 mV produced a fall in pHi that could be reduced by bathing the cell in nominally Ca2+‐free saline. 3. At positive holding potentials pHi increased to a steady level that depended upon the electrochemical gradient for H+ across the cell membrane; it shifted by about 1 unit when the external pH was increased from 7 to 8 (or when the membrane potential increased by 58 mV, Thomas & Meech, 1982). 4. The depolarization‐induced increase in H+ permeability was insensitive to SITS (4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid, 20 microM), which blocks pHi regulation at the resting potential in these cells (Thomas, 1976). When pHi was displaced from a steady level by ionophoretic injection of HCl, there was a rapid recovery at depolarized potentials even in the presence of SITS. The H+ pathway appeared to be little affected by prolonged periods at positive membrane potentials. 5. The depolarization‐induced H+ efflux was insensitive to the metabolic inhibitor CCmP (carbonyl cyanide‐m‐chlorophenylhydrazone, 20 microM) and persisted in cells bathed in pH‐buffered n‐methyl glucamine‐gluconate. It was also insensitive to DCCD (N, N'‐dicyclohexylcarbodiimide, 10‐100 microM) and oligomycin (2‐10 micrograms/ml). 6. The H+ pathway could be fully blocked by 1 mM‐ZnCl2, 1 mM‐LaCl3, 1 mM‐CuCl2, 2 mM‐CdCl2 or 10 mM‐CoCl2. Other divalent ions such as BaCl2 (10 mM) produced a block at membrane potentials near 0 mV but the block was released at more positive potentials. Low levels of LaCl3 (0.1 mM), the organic Ca2+ channel antagonist D600 (100 mg/ml) and high levels of the K+ channel blocker TEA (50 mM) all had similar effects to Ba2+. 7. The K+ channel blocker 4‐aminopyridine (10 mM), which blocks H+ currents in perfused Lymnaea neurones (Byerly, Meech & Moody, 1984), has a complex action.(ABSTRACT TRUNCATED AT 400 WORDS) © 1987 The Physiological Society