The Ionic Basis of the Depolarizing Mechanoreceptor Potential of Paramecium

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 Ca. 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 Ca at the concentrations tested, confirming the result of Ogura & Machemer (1980) that Ca is the major natural cation that carries the receptor current. Mg"", Si-"", Ba and Mrr can substitute for Ca in the generation of the depolarizing receptor potential. Except for Mn, this result is similar to that of de Peyer & Deitmer (1980) for Stylonychia. Na, K, Li and TEA"" cannot effectively substitute for Ca.