title: Application of an Epac activator enhances neurotransmitter release at excitatory central synapses.
abstract: cAMP regulates secretory processes through both PKA-independent and PKA-dependent signaling pathways. Their relative contributions to fast neurotransmission are unclear at present, although forskolin, which is generally believed to enhance intracellular cAMP levels by stimulation of adenylyl cyclase activity, was shown to increase vesicular release probability (p) and the number of releasable vesicles (N) in various neuronal preparations. Using low-frequency (0.2 Hz) electrophysiological recordings in the presence of the Epac-selective cAMP analog 8-pCPT-2'-O-Me-cAMP (ESCA(1)), we find that Epac activation by this analog accounts on average for 38% of the forskolin-induced increase in evoked EPSC amplitudes and for 100% of the forskolin-induced increase in miniature EPSC (mEPSC) frequency in dissociated autaptic neuronal cultures from mouse hippocampus. From paired-pulse facilitation experiments, and considering the enhancement of mEPSC frequency, we conclude that ESCA(1)-induced Epac activity is presynaptic in origin and increases p. In addition, preapplication of ESCA(1) augmented a subsequent enhancement of evoked EPSC amplitudes by phorbol ester (PDBu). This effect was maximal when ESCA(1) application preceded the PDBu application by 3 min. Because the PDBu response was abolished after downregulation of intracellular PKC activity, we conclude that ESCA(1)-induced Epac activation leads to presynaptic changes involving Epac-to-PKC signaling.
authors.affiliation: Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
authors.forename: Isabella
authors.initials: I
authors.lastname: Gekel
authors.forename: Erwin
authors.initials: E
authors.lastname: Neher
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D004334:Drug Administration Schedule; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000187:drug effects / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018377:Neurotransmitter Agents / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011336:Probability; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D013045:Species Specificity; D013569:Synapses / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism
chemical_list: C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D018377:Neurotransmitter Agents; D020033:Protein Isoforms; C526973:Rapgef3 protein, rat; D015240:Phorbol 12,13-Dibutyrate; D000242:Cyclic AMP; D011493:Protein Kinase C