Effects of SEPYLRFamide on acetylcholine-induced currents of Helix aspersa neurones: role of ryanodine receptors

Abstract

The possible participation of ryanodine receptors in the modulatory effects of the endogenous Helix heptapeptide, SEPYLRFamide, on the acetylcholine-induced currents (ACh-currents) of Helix aspersa neurones was studied using the two-electrode voltage clamp technique. SEPYLRFamide (bath application) caused a reduction of the ACh-currents of D1, D2, F1, F2, F76 and F77 neurones. Ryanodine (10 microM; bath application), which modifies ryanodine-controlled Ca(2+) channels, potentiated the inhibitory effect of SEPYLRFamide on the ACh-current. An antagonist of cyclic adenosine diphosphate ribose (cADPR) and ryanodine receptors, ruthenium red (1 mM; intracellular injection), reduced the inhibitory effects of SEPYLRFamide on the ACh-current. Ryanodine (10 microM) did not change the inhibitory effect of SEPYLRFamide on the ACh-current after intracellular injection of ruthenium red. An agonist of ryanodine receptors, caffeine (5 mM; bath application), reduced the ACh-current. Ryanodine (10 microM) did not change the reduction of ACh-currents induced by the first application of caffeine but decreased the reduction of ACh-currents induced by subsequent applications of caffeine. It is proposed that ryanodine receptors are involved in the inhibitory modulatory effects of SEPYLRFamide on somatic cholinergic receptors of Helix aspersa neurones.

Involvement of Na,K-pump in SEPYLRFamide-mediated reduction of cholinosensitivity in Helix neurons

“…Endogenous molluscan FMRFamide-related peptides (FaRPs): FMRFamide, SKPYMRFamide, SEPYLRFamide and its N-terminally modified analogues, EPYLRFamide, SEGYLRFamide, SRPYLRFamide, SKPYLRFamide and acetyl-SKPYMRFamide act as inhibitory neuromodulators of cholinergic transmission in H. aspersa [1,38,41] and Helix lucorum [36,39,40,42] parietal ganglia.…”

“…Our electrophysiological data show that intracellular free Ca 2+ is involved in the intracellular mechanism for the reduction of cholinosensitivity in Helix neurons by FaRPs [36,38,41]. Ryanodine receptors and IP 3 receptors may be involved in the inhibitory metabotropic effects of FaRPs on somatic cholinergic receptors of identified Helix neurons [36,38,41,42].…”

“…Previous work has shown that FMRFamide increases intracellular Ca 2+ via inhibition in Na out -dependent Ca 2+ -efflux (Na/Ca-exchange in the normal mode) [16,24,51] and activation of Ca 2+ -mobilization via ryanodine receptors and IP 3 receptors [18,19,36,38,41,54].…”