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The membrane potentials of Tetrahymena vorax

Connolly, John G. and Kerkut, G. A. (1981) The membrane potentials of Tetrahymena vorax. Comparative Biochemistry and Physiology Part C: Comparative Pharmacology, 69 (2). pp. 265-273. ISSN 0306-4492

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1. 1. Tetrahymena in a solution containing 1 mM CaCl2, 1 mM KCl, 1 mM TrisHCl pH 6.8, and 0.1 mM EDTAKOH had a resting potential of -28.7 ± 2.1 mV and a membrane resistance of 44.1 ± 2.6 MΩ. 2. 2. A 10-fold increase in external K+ led to a 28.3 mV change, and a 10-fold change in Ca2+ led to a 9.7 mV change in resting potential. 3. 3. Spontaneous hyperpolarizations were observed. These were of 150 msec duration, 12 mV magnitude and had a rate of change of potential of 220 mV sec-1. 4. 4. Spontaneous depolarizations were observed. There were of two main types: (a) the fast type had a maximum rate of rise of potential of 500 mV sec-1 with the spike peaking at + 10 mV. The depolarization phase lasted 100 msec and the repolarizing phase 400 msec. The fast spikes had an all-or-none characteristic and a threshold between 3 and 7 mV; and (b) the slow depolarizations did not overshoot 0 mV, were 15 mV in magnitude, with a rate of rise of potential of 50 mV sec-1. The time course was variable. Both fast and slow depolarizations could occur in the same cell. 5. 5. Following spikes, sustained depolarizations (plateaus) were observed in sodium free solutions. They had a variable duration and were usually at 0 mV membrane potential. 6. 6. Electrical stimulation elicited the fast type of depolarization in 80% of Tetrahymena. The response had an all-or-none characteristic and the threshold was 0.25 nA. 7. 7. The electrophysiological properties of Tetrahymena appear similar to but not identical with those of Paramecium.