Effect of measured calcium chloride injections on the membrane potential and internal pH of snail neurones.

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Abstract
Ion-sensitive microelectrodes were used to measure changes in intracellular pH (pHi) and internal Cl- which resulted from pressure injection of CaCl2 into identified Helix aspersa neurons. The internal Cl- measurement allowed the quantity of CaCl2 injected to be estimated. Application of the metabolic inhibitor carbonyl cyanide m-chlorophenyl hydrazone (CCmP) to a Ca-loaded cell caused an increase in membrane potential comparable to the effect of injecting Ca itself. The effect was not observed in normal cells. When injected in the presence of CCmp, Ca caused a much larger and longer-lasting effect on the membrane potential than that observed in untreated cells. Injection of ruthenium red can increase and/or prolong the hyperpolarization caused by a given quantity of injected Ca. The pHi changes following Ca injection were biphasic and slower than normal. In 7 experiments, both HCl and CaCl2 were injected into the same cell. Relative changes in pHi corresponded to the production of 1 H ion for each Ca ion injected. The relationship between the quantity of Ca injected and the size of the induced hyperpolarization suggested that at least 3 Ca ions acting cooperatively are required to activate a K channel. Injection of BaCl2 hyperpolarized the membrane after a delay of about 1 min. After several injections of Ba the cell lost this response while retaining its normal response to Ca injection. Injection of Ba also caused a slowly developing (biphasic) fall in pHi. Normally, injected Ca is rapidly taken up by mitochondria in exchange for H ions. If this uptake process is blocked by ruthenium red or CCmP, the Ca is taken up by a 2nd, slower process which also releases H ions. When pre-loaded, but not otherwise, the mitochondria will release Ca ions on treatment with CCmP. Injection of Ba does not directly affect the membrane conductance, but causes the release of Ca from intracellular binding sites.