SYNAPTIC TARGET CONTACT ENHANCES PRESYNAPTIC CALCIUM INFLUX BY ACTIVATING CAMP-DEPENDENT PROTEIN-KINASE DURING SYNAPTOGENESIS

Individual dissociated supralateral radular tensor (SLT) muscle fibers were manipulated into contact with fura-2-filled neurites of presynap tic buccal motoneuron 19 from Helisoma in cell culture. Within 30 min of contact, action potential-evoked calcium accumulation was reversibl y augmented from 228 +/- 82 nM to 803 +/- 212 nM, an action that was b locked by H-7 (40-100 muM). Calcium accumulation was not augmented whe n buccal motoneuron 19 contacted muscle or neuronal targets with which it does not form chemical synapses. Addition of pCPTcAMP (500 muM) to cultures reversibly enhanced calcium accumulation. Injection of IP20, a peptide inhibitor of cAMP-dependent protein kinase, prevented pCPTc AMP and SLT muscle from enhancing calcium accumulation. These data dem onstrate that SLT muscle target retrogradely regulates calcium accumul ation in presynaptic nerve terminals by locally activating presynaptic cAMP-dependent protein kinase.