Summary
Hyperpolarization of voltage-clampedParamecium tetraurelia in K+ solutions elicits a complex of Ca2+ and K+ currents. The tail current that accompanies a return to holding potential (−40 mV) contains two K+ components. The tail current elicited by a step to −110 mV of ≥50-msec duration contains fast-decaying (τ≈3.5 msec) and slow-decaying (τ≈20 msec) components. The reversal potential of both components shifts by 55–57 mV/10-fold change in external [K+], suggesting that they represent pure K+ currents. The dependence of the relative amplitudes of the two tail currents on duration of hyperpolarization suggests that the slow K+ current activates slowly and is sustained, whereas the fast current activates rapidly during hyperpolarization and then rapidly inactivates. Iontophoretic injection of a Ca2+ chelator, EGTA, specifically reduces slow tail-current amplitude without affecting the fast tail component. Both K+ currents are inhibited by extracellular TEA+ in a concentration-dependent, noncooperative manner, whereas the fast K+ current alone is inhibited by 0.7mm quinidine.
Similar content being viewed by others
References
Eckert, R., Brehm, P. 1979. Ionic mechanisms of excitation inParamecium.Annu. Rev. Biophys. Bioeng. 8:353–383
Hansma, H. 1974. Biochemical studies on the behavioral mutants ofParamecium aurelia: Ion fluxes and ciliary membrane proteins. Ph.D. Thesis. University of California, Santa Barbara
Hennessey, T.M. 1987. A novel calcium current is activated by hyperpolarization ofParamecium tetraurelia.Soc. Neurosci. 13:108 (Abstr.)
Hille, B. 1984. Ionic Channels of Excitable Membranes. Sinauer, New York
Hinrichsen, R.D., Saimi, Y. 1984. A mutation that alters properties of the calcium channel inParamecium tetraurelia.J. Physiol. (London) 351:397–410
Katz, B. 1949. Les constantes électriques de la membrane du muscle.Arch. Sci. Physiol. 2:285–299
Kung, C., Saimi, Y. 1982. The physiological basis of taxes inParamecium.Annu. Rev. Physiol. 44:519–534
Machemer, H. 1988a. Electrophysiology.In:Paramecium. H.-D. Görtz, editor. pp. 183–215. Springer-Verlag, Berlin
Machemer, H. 1988b. Motor control of cilia.In:Paramecium. H.-D. Görtz, editor. pp. 216–235. Springer-Verlag, Berlin
Naitoh, Y., Eckert, R. 1972. Electrophysiology of the ciliate protozoa.In: Experiments in Physiology and Biochemistry. G.A. Kerkut, editor. pp. 17–31. Academic, New York
Oertel, D., Schein, S.J., Kung, C. 1978. A potassium conductance activated by hyperpolarization inParamecium.J. Membrane Biol. 43:169–185
Ogura, A., Machemer, H. 1980. Distribution of mechanoreceptor channels in theParamecium surface membrane.J. Comp. Physiol. 135:233–242
Preston, R.R., Saimi, Y., Amberger, E., Kung, C. 1990a. Interactions between mutants with defects in two Ca2+-dependent K+ currents ofParamecium tetraurelia.J. Membrane Biol. 115:61–69
Preston, R.R., Wallen-Friedman, M.A., Saimi, Y., Kung, C. 1990b. Calmodulin defects cause the loss of Ca2+-dependent K+ currents in two pantophobiac mutants ofParamecium tetraurelia.J. Membrane Biol. 115:51–60
Richard, E.A., Hinrichsen, R.D., Kung, C. 1985. A single gene mutation that affects a potassium conductance and resting membrane potential inParamecium.J. Neurogenet. 2:239–252
Richard, E.A., Saimi, Y., Kung, C. 1986. A mutation that increases a novel calcium-activated potassium conductance ofParamecium tetraurelia.J. Membrane Biol. 91:173–181
Rudy, B. 1988. Diversity and ubiquity of K channels.Neuroscience 25:729–749
Saimi, Y. 1986. Calcium-dependent sodium currents inParamecium: Mutational manipulations and effects of hyper- and depolarization.J. Membrane Biol. 92:227–236
Saimi, Y., Hinrichsen, R.D., Forte, M., Kung, C. 1983. Mutant analysis shows that the Ca2+-induced K+ current shuts off one type of excitation inParamecium.Proc. Natl. Acad. Sci. USA 80:5112–5116
Saimi, Y., Kung, C. 1987. Behavioral genetics ofParamecium.Annu. Rev. Genet. 21:47–65
Satow, Y., Kung, C. 1977. A regenerative hyperpolarization inParamecium.J. Comp. Physiol. 119:99–110
Sauvé, R., Simoneau, C., Monette, R., Roy, G. 1986. Single-channel analysis of the potassium permeability in HeLa cancer cells: Evidence for a calcium-activated potassium channel of small unitary conductance.J. Membrane Biol. 92:269–282
Sauvé, R., Simoneau, C., Parent, L., Monette, R., Roy, G. 1987. Oscillatory activation of calcium-dependent potassium channels in HeLa cells induced by histamine H1 receptor stimulation: A single channel study.J. Membrane Biol. 96:199–208
Sonneborn, T.M. 1975.Paramecium aurelia.In: Handbook of Genetics. R.C. King, editor. Vol. II. pp. 469–594. Plenum, New York
Yeh, J.Z., Narahashi, T. 1976. Mechanism of action of quinidine on squid axon membranes.J. Pharmacol. Exp. Ther. 196:62–70
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Preston, R.R., Saimi, Y. & Kung, C. Evidence for two K+ currents activated upon hyperpolarization ofParamecium tetraurelia . J. Membrain Biol. 115, 41–50 (1990). https://doi.org/10.1007/BF01869104
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF01869104