Osmotic Tolerance of Ca-Dependent Excitability in the Marine Ciliate Paramecium Calkinsi

Abstract

The electrical membrane properties of the marine (brackish-water) ciliate Paramecium calkinsi were investigated under constant-current and voltage-clamp conditions, using two intracellular microelectrodes. The action potential and membrane currents were extremely tolerant to changes in the salinity of the bathing medium. Current-voltage relationships exhibited a moderate inward-going rectification of the membrane upon hyperpolarization, and a prominent outward-going rectification upon depolarization of the membrane. Ion substitution experiments showed that the electrically excitable response is a graded Ca2+-action potential, similar to that found in freshwater ciliates.