Electrophysiological studies of the protozoan, Stentor coeruleus.

Transmembrane potentials and membrane characteristics of Stentor coeruleus were studied by means of microelectrodes and standard electrophysiological techniques. Intracellular resting potentials were found to be variable and recordable for only a brief span of time owing to the encapsulation of the recording electrodes. During this brief time span of recorded resting potentials were anamolous in that they were generally of positive polarity. When an extended Stentor was stimulated to contract, a 10-60 mv negative-going transient response was recorded from intracellular electrodes. After the electrodes had been encapsulated, a diphasic transient response was observed when the penetrated animal contracted. Simultaneous recordings from intracellular and encapsulated electrodes showed that the diphasic and negative-going transient responses occurred simultaneously. Contractions of Stentor occurred in 7 to 8 msec following a 2 to 3 msec latent period after a suprathreshold shock. Records obtained by use of a photomultiplier and microelectrodes indicated that the contractions began 1.8 msec after the onset of the diphasic response. Prepotentials were observed prior to mechanically stimulated responses.