An electrophysiological study of the tentacle-regulating potentials in Noctiluca.

In the preceding paper the movements of the food-gathering tentacle of the marine dinoflagellate Noctiluca mtUaris were shown to be temporally related to spontaneous potential patterns in a manner which indicates that the potential changes are involved in the control of tentacle movements (Eckert & Sibaoka, 1967). The spontaneous potentials were therefore termed tentacle-regulating potentials (TRPs) to distinguish them from the action potential which triggers light emission from organelles in the perivacuolar cytoplasm (Eckert, 1965 a, b; Eckert & Reynolds, 1967). The basic TRP, recorded from the vacuole, consists of a positive-going pre-spike wave which reaches a peak of about —10 mV before undergoing a slow negative shift which terminates in the negative-going TR spike. A post-spike d.c. level is maintained for variable durations at — 45 to — 60 mV. The vacuolar potential alternates cyclically and spontaneously between the preand post-spike levels. In this paper the nature and origin of the TRP are explored by examining the influence of passive and active potential changes on the potential wave pattern, by measurements of local impedance changes and of recordings of electrical potential from the surface, the vacuole and the cytoplasm. The evidence indicates that the TRP complex consists of two basic components: a pacemaker potential and a prolonged action potential. Both originate in or near the base of the tentacle. Unlike the flash-triggering action potential, TRP activity does not propagate over the perivacuolar cytoplasm.