Kd. Clark et al., EXTERNAL GTP ALTERS THE MOTILITY AND ELICITS AN OSCILLATING MEMBRANE DEPOLARIZATION IN PARAMECIUM-TETRAURELIA, Proceedings of the National Academy of Sciences of the United Statesof America, 90(9), 1993, pp. 3782-3786
Paramecium, a unicellular ciliated protist, alters its motility in res
ponse to various stimuli. Externally added GTP transiently induced alt
ernating forward and backward swimming interspersed with whirling at a
concentration as low as 0.1 muM. ATP was 1000-fold less active, where
as CTP and UTP produced essentially no response. The response to the n
onhydrolyzable GTP analogs guanosine 5'-[gamma-thio]triphosphate and g
uanosine 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 ce
lls and the mutant pawn B, which is defective in the voltage-dependent
Ca2+ current required for action potentials. This is a specific effec
t of external GTP on the excitability of a eukaryotic cell and, to our
knowledge, is the first purinergic effect to be discovered in a micro
organism.