Inhibitory effect of cyclic guanosine 3 ',5 '-monophosphate (cGMP) on the afferent resting activity in the cephalopod statocyst

The effects of exo- and endogenous cGMP on the resting activity (RA) of aff erent crista fibers were studied in isolated preparations of the statocysts of the cuttlefish Sepia officinalis and the squid Sepioteuthis lessoniana. Bath application of the membrane-permeable cGMP analogs 8-brumo-cGMP (B-cG MP) and N-2,2'-o-dibutyryl 3',5'-cyclic guanosine monophosphate (dB-cGMP), and of the selective inhibitor of cGMP-phosphodiesterase zaprinast (ZAP), c aused an inhibition of RA. The inhibitory effects of B-cGMP and dB-cGMP rem ained when the preparation was pre-treated with: (i) the guanylate cyclase inhibitors 1H-[1,2,4]oxadiazolo[4,3,-alpha ]quinoxalin-1-one (ODQ) or cysta mine (CYS); (ii) the adenylate cyclase inhibitors nicotinic acid (NIC-A), 2 ',3'dideoxyadenosine (DDA), or MDL-12330A (MDL); (iii) the guanylate cyclas e inhibitor methylene blue (M-BLU) and the adenylate cyclase inhibitor MDL combined; or (iv) the nitric oxide (NO) synthase inhibitors N-G-nitric-L-ar ginine methyl ester HCl (L-NAME) or N-G-nitro-L-arginine (L-NOARG). These d ata indicate that cGMP, as an intracellular messenger, has a tonic inhibito ry effect on the RA of afferent crista fibers in cephalopod statocysts. (C) 2000 Elsevier Science B.V. All rights reserved.