Bioelectric regulation of tentacle movement in a dinoflagellate.

Studies of contractile responses and their control by electroionic mechanisms have been performed primarily on vertebrate muscle (Huxley & Taylor, 1958; Hodgkin & Horowicz, 1960; Sandow, Taylor & Preiser, 1965); however, mechanical responses correlated with bioelectric potentials also occur in a number of other cells in both the animal and plant (Sibaoka, 1966) kingdoms. The Protozoa, especially, include many examples. Mechanical phenomena in the protozoa which have been examined by electrophysiological or ionic methods include the reversal of ciliary beat in Paramecium (Kamada, 1940; Kinosita, 1954; Naitoh, 1964, 1966), metachronal coordination in Opalina (Okajima, 1953; Naitoh, 1961), streaming in Amoeba (Bingley & Thompson, 1962; Bingley, 1966), and stalk contraction in Vorticella and Carchesium (Hou & Briicke, 1931; Ueda, 1954; Sugi, 1959, i960). All unicellular forms which have thus far lent themselves to electrophysiological methods exhibit some electrical and/or ionic correlates with mechanical activity. Because of the phyletic and functional diversity of motile systems found in these organisms their investigation should contribute to broadly based concepts of the control and coordination of cell movement. The dinoflagellate Noctiluca has two functionally separate excitable systems. One, evoked by stimulation, triggers luminescence (Eckert, 1965 a, b, 1966, 1967; Eckert & Reynolds, 1967), and the other, normally spontaneous, regulates movements of the food-gathering tentacle (Hisada, 1957; unpublished observations of Watanabe and Hagiwara mentioned by Bullock & Horridge, 1965; Eckert, 1965 c). The existence in one cell of two functionally distinct excitable systems for the regulation of qualitatively different secondary responses is in itself of interest and will be considered in more detail elsewhere. In this paper attention is focused on some elementary properties of the tentacleregulating potentials (TRPs), and the movements of the tentacle which occur in response to the potential pattern. Finally, brief evidence is presented for the structural basis of tentacle contractility, and for the essential role of calcium ions in tentacle contraction. A preliminary report has appeared elsewhere (Eckert, 1965 c). The accompanying paper (Sibaoka & Eckert, 1967) further explores the electrical properties of the TRPs and their site of origin.