Hyperpolarization- and depolarization-activated Ca2+ currents in Paramecium trigger behavioral changes and cGMP formation independently.
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.
Schultz
J E
JE
Faculty of Chemistry and Pharmacy, University of Tübingen, 72076 Tübingen, Germany.
Guo
Y
Y
Kleefeld
G
G
Völkel
H
H
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000172:deficiency / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002923:Cilia / Q000187:drug effects; D003078:Colchicine / Q000494:pharmacology; D006152:Cyclic GMP / Q000096:biosynthesis*; D000431:Ethanol / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008124:Locomotion / Q000187:drug effects*; D008564:Membrane Potentials; D016805:Paramecium tetraurelia / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D015220:Calcium Channels; D000431:Ethanol; D000584:Amiloride; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D003078:Colchicine; D002118:Calcium