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The Journal of Neuroscience, August 6, 2008, 28(32):7991-8002; doi:10.1523/JNEUROSCI.0268-08.2008

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Cellular/Molecular
Application of an Epac Activator Enhances Neurotransmitter Release at Excitatory Central Synapses

Isabella Gekel and Erwin Neher

Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany

Correspondence should be addressed to Erwin Neher, Max Planck Institute for Biophysical Chemistry, Department of Membrane Biophysics, Am Fassberg 11, 37077 Göttingen, Germany. Email: eneher{at}gwdg.de

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 (ESCA₁), 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 ESCA₁-induced Epac activity is presynaptic in origin and increases p. In addition, preapplication of ESCA₁ augmented a subsequent enhancement of evoked EPSC amplitudes by phorbol ester (PDBu). This effect was maximal when ESCA₁ application preceded the PDBu application by 3 min. Because the PDBu response was abolished after downregulation of intracellular PKC activity, we conclude that ESCA₁-induced Epac activation leads to presynaptic changes involving Epac-to-PKC signaling.

Key words: cAMP; Epac; vesicular release probability; excitatory autaptic neurons; PKC; glutamatergic synapse

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Received Oct. 17, 2007; revised June 25, 2008; accepted July 1, 2008.

Correspondence should be addressed to Erwin Neher, Max Planck Institute for Biophysical Chemistry, Department of Membrane Biophysics, Am Fassberg 11, 37077 Göttingen, Germany. Email: eneher{at}gwdg.de

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