Cyclic AMP synchronizes evoked quantal release at frog neuromuscular junctions

At frog neuromuscular junction, noradrenaline (NA) shortens the release per iod for evoked quantal release acting on a beta 1 receptor. To test the hyp othesis that this action of NA is mediated by cAMP, we measured the latenci es of focally recorded uni-quantal endplate currents (EPCs) after applicati on of dibutyryl-cAMP (db-cAMP) and adenylyl cyclase activator, forskolin. T he interval between the time when responses with minimal delay appeared and the point at which 90% of all latencies had occurred (P-90 parameter) was shortened in the presence of both 1x10(-6) mol/l db-cAMP and 1x 10(-6) mol/ l forskolin by about 30%. The cAMP-induced shortening is equal to that foun d after application of NA and effects of both drugs are not additive.