M. Walerczyk et S. Fabczak, Alterations of photophobic motile response in Stentor by cyclic guanosine 3 ',5 '-monophosphate-elevating agents, ACT PROTOZ, 40(2), 2001, pp. 153-157
The effects of exogenous cyclic nucleotides and modulators of the cyclic nu
cleotide signaling pathway on the step-up photophobic response have been st
udied in the ciliate Stenter coeruleus. To attain this, the latency time fo
r the ciliary stop response and the ciliary reversal duration has been esti
mated using microscope videorecording and dark-field macro-photography. Mem
brane-permeable, slowly hydrolyzable analogs of cyclic GMP, 8-Br-cGMP and d
b-cGMP, significantly increase the latency time of ciliary stop response an
d decrease the period of ciliary reversal. By contrast, cyclic AMP analogs,
8-Br-cAMP or db-cAMP, had no measurable effect on the photophobic response
parameters. The effects of the exogenous cGMP are mimicked by the applicat
ion of the non-specific PDE inhibitor IBMX or zaprinast, a specific cGMP-PD
E inhibitor. These behavioral observations suggest that in vivo, the intern
al level of presumed cGMP, but not cAMP, is possibly a limiting factor for
the time course of the motile avoiding response of Stenter, and they furthe
r support the hypothesis that cGMP metabolism may play a role in photosigna
l transduction in these cells.