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

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 μM; bath application), which modifies ryanodine-controlled Ca²⁺ 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 μM) 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 μM) 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. Accepted: 1 July 1998