ACTION OF PROTEIN-KINASE-A ACTIVATORS ON THE CAUDAL NEUROMUSCULAR-JUNCTION OF TOAD TADPOLES, RECORDED ON SYNAPTIC SPOTS

Miniature end-plate currents (MEPCS), from synaptic spots on the cauda l muscles of Bufo marinus tadpoles, were analyzed in both pre- and pos tsynaptic domains, when protein kinase A (PKA) activity modificators w ere used. Sp-cAMPS diasteromer induced an increase in MEPC frequency, which was completely reversed by Rp-cAMPS. However, changes in the dec ay time of MEPCS were not detected. Dibutyryl-cAMP produced a similar presynaptic action, but its postsynaptic action was similar to butyrat e. Presynaptic effect of forskolin (FSK), if any, is masked by the inc rease of MEPC frequency produced by dimethylsulfoxide (DMSO), the solv ent used.