Effects of intracellular pH and calcium activity on ion currents in internally perfused neurons of the snail Lymnaea stagnalis

Abstract

The suction pipet method of intracellular dialysis and voltage clamp of cells has proven extremely useful in analysing the electrical properties of cells too small for the application of conventional microelectrode techniques and in larger cells for studying the effects of alterations in the internal ionic composition. Using neurons of the snail Lymnaea stagnalis, we have analysed several problems involved in the latter application of this technique and present several solutions to them. One major problem centers around the degree of control over the ionic composition of the cytoplasm achieved by altering the pipet solution. Using ion-sensitive microelectrodes during internal dialysis, we found that the efficiency of exchange between pipet and cytoplasm was much poorer for highly buffered ions such as H+ and Ca2+, than for K+, for example. Special precautions are described that can help this situation. The second problem involves the study of the effects of low internal pH on ion-channel properties. We summarize evidence for a specific voltage-dependent hydrogen ion channel, current through which becomes prominent at low internal pH. We analyse how the presence of this heretofore unrecognized current can seriously confuse the results of experiments designed to study the effects of low internal pH on other voltage-dependent currents.