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

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.