The Ionic Basis of the Depolarizing Mechanoreceptor Potential of Paramecium Tetraurelia

A depolarizing receptor potential produced by mechanical stimulation was studied in pawn mutants of Paramecium tetraurelia bathed in TEA solution. The potential was dependent upon the strength of the mechanical stimulation until a maximum response was reached. The maximum value was dependent on the concentration of external Ca2+. Discounting the change in resting potential (attributable to change in surface charge), the maximal receptor potential changed by 20 mV per 10-fold change in Ca2+ at the concentrations tested, confirming the result of Ogura & Machemer (1980) that Ca2+ is the major natural cation that carries the receptor current. Mg2+, Sr2+, Ba2+ and Mn2+ can substitute for Ca2+ in the generation of the depolarizing receptor potential. Except for Mn2+, this result is similar to that of de Peyer & Deitmer (1980) for Stylonychia. Na+, K+, Li++ and TEA+ cannot effectively substitute for Ca2+.