A regenerative calcium response in Paramecium.

The electric properties of Paramecium have gained interest because of the emerging role of membrane potential and conductance in the control of ciliary activity (Kinosita, 1954; Okajima, 1953; Naitoh, 1958; Kinosita, Murakami & Yasuda, 1965; Naitoh & Eckert, 1969a, b; Eckert & Naitoh, 1970). Recent evidence indicates that ciliary responses are coupled to membrane potential by membrane-regulated calcium fluxes (Eckert, 1972). Membrane potential changes occur in response to mechanical stimuli (Naitoh & Eckert, 1969 a, b), radiant energy (Hildebrand, 1970), and changes in extracellular electrolyte concentration (Kamada, 1934; Naitoh & Eckert, 1968a). Further interest comes from the isolation of behavioural mutant of Paramecium (Kung, 1971) which has lost the property of regenerative depolarization characteristic of the wild-type membrane (Kung & Eckert, 1972). The cell membrane of Paramecium normally produces a graded, spike-like, regenerative response to applied outward current (Eckert & Naitoh, 1969). This is followed closely in time by a re-orientation of the cilia so that the direction of the effective stroke (and, hence, the direction of swimming) is reversed (Eckert & Naitoh, 1970). A similar graded response is produced by the depolarization in response to mechanical stimulation of the anterior surface of Paramecium (Eckert, Naitoh & Friedman, 1972). In this paper we present evidence that the graded response is dependent on extracellular Ca*, and propose that the membrane of Paramecium undergoes an increase in calcium permeability in response to depolarization, which permits Ca"" to flow inward down its electrochemical gradient. The regenerative response in Paramecium is similar in this and several other respects to the graded, non-propagated responses produced by crustacean muscle (Fatt & Katz, 1953; Fart & Ginsborg, 1958; Werman & Grundfest, 1961).