title: Muscarinic stimulation of synaptic activity by protein kinase C is inhibited by adenosine in cultured hippocampal neurons.
abstract: We have studied the effect of the cholinergic agonist carbachol on the spontaneous release of glutamate in cultured rat hippocampal cells. Spontaneous excitatory postsynaptic currents (sEPSCs) through glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type channels were recorded by means of the patch-clamp technique. Carbachol increased the frequency of sEPSCs in a concentration-dependent manner. The kinetic properties of the sEPSCs and the amplitude distribution histograms were not affected by carbachol, arguing for a presynaptic site of action. This was confirmed by measuring the turnover of the synaptic vesicular pool by means of the fluorescent dye FM 1-43. The carbachol-induced increase in sEPSC frequency was not mimicked by nicotine, but could be blocked by atropine or by pirenzepine, a muscarinic cholinergic receptor subtype M1 antagonist. Intracellular Ca2+ signals recorded with the fluorescent probe Fluo-3 indicated that carbachol transiently increased intracellular Ca2+ concentration. Since, however, carbachol still enhanced the sEPSC frequency in bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate-loaded cells, this effect could not be attributed to the rise in intracellular Ca2+ concentration. On the other hand, the protein kinase inhibitor staurosporine as well as a down-regulation of protein kinase C by prolonged treatment of the cells with 4beta-phorbol 12-myristate 13-acetate inhibited the carbachol effect. This argues for an involvement of protein kinase C in presynaptic regulation of spontaneous glutamate release. Adenosine, which inhibits synaptic transmission, suppressed the carbachol-induced stimulation of sEPSCs by a G protein-dependent mechanism activated by presynaptic A1-receptors.
authors.affiliation: Department of Pharmacology, University of Berne, Friedbuehlstrasse 49, CH-3010 Berne, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Bouron
authors.forename: H
authors.initials: H
authors.lastname: Reuter
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004789:Enzyme Activation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D018091:Receptors, AMPA; D011976:Receptors, Muscarinic; D001285:Atropine; D002217:Carbachol; D011493:Protein Kinase C; D019311:Staurosporine; D000241:Adenosine; D002118:Calcium