Hyperpolarization- and Depolarization-activated Ca2+ Currents in Paramecium Trigger Behavioral Changes and cGMP Formation Independently |
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Authors: | JE Schultz Y-L Guo G Kleefeld H Völkel |
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Institution: | (1) Faculty of Chemistry and Pharmacy, University of Tübingen, 72076 Tübingen, Germany, DE |
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Abstract: | Using 5% ethanol as a deciliating agent, 20 mm colchicine to prevent reciliation and 1 mm amiloride to affect ion fluxes in Paramecium we examined the compartmentation and function of Ca2+ fluxes employing the biosynthesis of cGMP and the stereotypic swimming behavior as indicators for Ca2+ entry. As a function of extracellular Ca2+
Paramecia responded to colchicine and amiloride with a short-lived ciliary augmentation (fast swimming) which indicated hyperpolarization,
and formation of cGMP, i.e., the reported hyperpolarization-activated Ca2+ inward current in the somatic membrane is coupled to intracellular generation of cGMP. This is comparable to the coupling
of the depolarization-activated, ciliary Ca2+ inward current and ciliary cGMP formation.
Ethanol-deciliated cells and ethanol-treated, yet ciliated control cells did not respond to a depolarization with backward
swimming or formation of cGMP. Both responses recovered with similar kinetics. A persistent effect of an ethanol exposure
on the axonemal apparatus or on guanylyl cyclase activity of ciliated control cells was excluded using permeabilized cells
and cell-free enzyme, respectively. Further, in the presence of 20 mm colchicine ethanol-treated cells only recovered the depolarization-dependent avoiding reaction whereas the formation of cGMP
remained depressed, i.e., the drug dissected both responses. Similarly, ethanol exposure of Paramecia did not affect the fast swimming response towards the hyperpolarizing agent amiloride whereas the cGMP formation was abrogated
and recovered over a period of 7 hr, i.e., amiloride dissected the hyperpolarization-elicited behavioral response from the
intracellular cGMP formation.
The data demonstrate that in Paramecium depolarization- and hyperpolarization-stimulated behavioral responses and cGMP formation are not coupled. The behavioral
changes are triggered by smaller Ca2+ inward currents than the formation of intracellular cGMP.
Received: 8 August 1996/Revised: 15 November 1996 |
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Keywords: | : Paramecium — cGMP — Ca2+ channel — Hyperpolarization |
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