Effects of nystatin on membrane conductance and internal ion activities in Aplysia neurons.

Two methods were used to study effects of the antibiotics, nystatin, on giant neurons of Aplysia. In the first method the effects of various concentrations of nystatin on the current-voltage relationship were evaluated at a fixed time after exposure to the antibiotic using a two-microelectrode voltage clamp. Nystatin increased membrane conductance in a dose-dependent manner. The dose-response relation was very steep, with little or no effect below 15 mg/liter and an effect too large to measure at concentrations greater than 30 mg/liter. Upon return to antibiotic-free solution, membrane conductance returned to pre-treatment levels within 30 minutes. The second type of experiment involved use of ion-specific microelectrodes to measure changes of intracellular univalent ion activities which attended the nystatin-induced permeability. Nystatin-induced permeability changes mainly involved univalent cations, but Cl permeability was also increased. Nystatin may therefore be used to selectively rearrange the internal ionic milieu to study the effect of such a change on membrane transport or electrical properties.