The effect of calcium injection on the intracellular sodium and pH of snail neurones.

Abstract

Ion-sensitive glass microelectrodes were used to measure the intracellular pH (pHi) and the intracellular Na+ concentration, [Na+]i, in identified Helix aspersa neurons. The injection of small volumes of 0.1 M-CaCl2, which increased the membrane potential by 10-15 mV for 1-2 min, had little or no effect on [Na+]i. Increases of up to 1 mM in [Na+]i could be reversibly induced by larger injections. Ca injection caused an immediate decrease in pHi, which appeared directly proportional to the amount of Ca injected. Injections causing hyperpolarizations of 10-20 mV which recovered in 2-5 min caused pHi decreases of 0.04-0.15 units. After each of these injections both pHi and membrane potential recovered exponentially but with different time constants. Injection of Ca at a low rate could decrease pHi without affecting membrane potential. Neither membrane potential nor pHi were affected by the injection of small volumes of 0.1 M-MgCl2. Injection of CoCl2 produced a large transient decrease in pHi but no significant change in membrane potential. Exposure of the cell to saline equilibrated with 2.5% CO2 greatly reduced the pHi decrease caused by Ca injection but had only small effects on membrane potential response. Most of the injected Ca is exchanged for protons inside the cell.