The role of bicarbonate, chloride and sodium ions in the regulation of intracellular pH in snail neurones

Abstract

1. Intracellular pH (pH i), Cl− and Na+ levels were recorded in snail neurones using ion‐sensitive micro‐electrodes, and the mechanism of the pH i recovery from internal acidification investigated. 2. Reducing the external HCO 3− concentration greatly inhibited the rate of pH i recovery from HCl injection. 3. Reducing external Cl− did not inhibit pH i recovery, but reducing internal Cl−, by exposing the cell to sulphate Ringer, inhibited pH i recovery from CO 2 application. 4. During pH i recovery from CO 2 application the internal Cl− concentration decreased. The measured fall in internal Cl− concentration averaged about 25% of the calculated increase in internal HCO 3−. 5. Removal of external Na inhibited the pH i recovery from either CO 2 application or HCl injection. 6. During the pH i recovery from acidification there was an increase in the internal Na+ concentration ([Na+]i). The increase was larger than that occurring when the Na pump was inhibited by K‐free Ringer. 7. The increase in [Na+]i that occurred during pH i recovery from an injection of HCl was about half of that produced by a similar injection of NaCl. 8. The inhibitory effects of Na‐free Ringer and of the anion exchange inhibitor SITS on pH i recovery after HCl injection were not additive. 9. It is concluded that the pH i regulating system involves tightly linked Cl−‐HCO 3− and Na+‐H+ exchange, with Na entry down its concentration gradient probably providing the energy to drive the movement inwards of HCO 3− and the movement outward of Cl− and H+ ions.