Cyclic AMP synchronizes evoked quantal release at frog neuromuscular junctions

Abstract

At frog neuromuscular junction, noradrenaline (NA) shortens the release period for evoked quantal release acting on a β1 receptor. To test the hypothesis that this action of NA is mediated by cAMP, we measured the latencies of focally recorded uni-quantal endplate currents (EPCs) after application of dibutyryl-cAMP (db-cAMP) and adenylyl cyclase activator, forskolin. The interval between the time when responses with minimal delay appeared and the point at which 90% of all latencies had occurred (P90 parameter) was shortened in the presence of both 1x10-6 mol/1 db-cAMP and 1x10-6 mol/1 forskolin by about 30%. The cAMP-induced shortening is equal to that found after application of NA and effects of both drugs are not additive.