External GTP alters the motility and elicits an oscillating membrane depolarization in Paramecium tetraurelia.
Paramecium, a unicellular ciliated protist, alters its motility in response to various stimuli. Externally added GTP transiently induced alternating forward and backward swimming interspersed with whirling at a concentration as low as 0.1 microM. ATP was 1000-fold less active, whereas CTP and UTP produced essentially no response. The response to the nonhydrolyzable GTP analogs guanosine 5'-[gamma-thio]triphosphate and guanosine 5'-[beta, gamma-imido]triphosphate was indistinguishable from that to GTP. This behavioral response was correlated with an unusual transient and oscillating membrane depolarization in both wild-type cells and the mutant pawn B, which is defective in the voltage-dependent Ca2+ current required for action potentials. This is a specific effect of external GTP on the excitability of a eukaryotic cell and, to our knowledge, is the first purinergic effect to be discovered in a microorganism.
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706.
K D
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Clark
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Hennessey
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Nelson
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects; D006150:Guanine Nucleotides / Q000494:pharmacology; D006151:Guanosine / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000494:pharmacology; D006157:Guanosine Monophosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016805:Paramecium tetraurelia / Q000187:drug effects / Q000502:physiology*; D012265:Ribonucleotides / Q000494:pharmacology
D006150:Guanine Nucleotides; D012265:Ribonucleotides; D006151:Guanosine; D006153:Guanosine Diphosphate; D006157:Guanosine Monophosphate; D006160:Guanosine Triphosphate