Involvement of ryanodine receptors in EPYLRFamide-mediated reduction of acetylcholine-induced inward currents in Helix lucorum identified neurones

The effects of several modulators of ryanodine receptors (RYRs) on the redu ction of acetylcholine induced inward current (ACh-current) evoked by EPYLR Famide (5 mu M, bath application), the potent N-terminally modified analogu e of the endogenous Helix heptapeptide SEPYLRFamide, were investigated. The se modulators were applied intracellularly. Inward currents were recorded f rom identified Helix lucorum LPa2, LPa3, RPa3, RPa2 neurones in ganglia pre parations using the two-electrode voltage clamp technique. ACh was applied ionophoretically. BAPTA (0.1 mM), chelator of intracellular Ca2+, ryanodine (0.1 mM), agonist/antagonist of RYRs and dantrolene (0.1 mM), antagonist o f RYRs decrease the effect of EPYLRFamide. Adenosine (1 mM), alpha,beta-met hylene ATP (0.1 mM), the nonhydrolisable ATP analogue and cyclic adenosine diphosphate ribose (0.1 mM) (agonists of RYRs) potentiate the modulatory ef fect of EPYLRFamide. Ruthenium red (1 mM), antagonist of RYRs and caffeine (1 mM), agonist of RYRs do not change the modulatory effect of EPYLRFamide. These data suggest that intracellular Ca2+ and RYRs are involved in the mo dulatory effect of EPYLRFamide on ACh-currents. It was concluded that EPYLR Famide decreases ACh-current through elevation of basal intracellular level of a putative endogenous agonist of RYRs which activates RYR-dependent mob ilization of Ca2+ by binding to the adenine nucleotide site of the ryanodin e receptor-channel complex and does not bind the site activated by caffeine . (C) 2000 Elsevier Science B.V. All rights reserved.