title: Adenosine receptor expression and modulation of Ca(2+) channels in rat striatal cholinergic interneurons.
abstract: Adenosine is a potent regulator of acetylcholine release in the striatum, yet the mechanisms mediating this regulation are largely undefined. To begin to fill this gap, adenosine receptor expression and coupling to voltage-dependent Ca(2+) channels were studied in cholinergic interneurons by combined whole cell voltage-clamp recording and single-cell reverse transcription-polymerase chain reaction. Cholinergic interneurons were identified by the presence of choline acetyltransferase mRNA. Nearly all of these interneurons (90%, n = 28) expressed detectable levels of A(1) adenosine receptor mRNA. A(2a) and A(2b) receptor mRNAs were less frequently detected. A(3) receptor mRNA was undetectable. Adenosine rapidly and reversibly reduced N-type Ca(2+) currents in cholinergic interneurons. The A(1) receptor antagonist 8-cyclopentyl-1, 3-dimethylxanthine completely blocked the effect of adenosine. The IC(50) of the A(1) receptor selective agonist 2-chloro-N6-cyclopentyladenosine was 45 nM, whereas it was near 30 microM for the A(2a) receptor agonist CGS-21680. Dialysis with GDPbetaS or brief exposure to the G protein (G(i/o)) alkylating agent N-ethylmaleimide also blocked the adenosine modulation. The reduction in N-type currents was partially reversed by depolarizing prepulses. A membrane-delimited pathway mediated the modulation, because it was not seen in cell-attached patches when agonist was applied to the bath. Activation of protein kinase C attenuated the adenosine modulation. Taken together, our results argue that activation of A(1) adenosine receptors in cholinergic interneurons reduces N-type Ca(2+) currents via a membrane-delimited, G(i/o) class G-protein pathway that is regulated by protein kinase C. These observations establish a cellular mechanism by which adenosine may serve to reduce acetylcholine release.
authors.affiliation: Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
authors.forename: W J
authors.initials: WJ
authors.lastname: Song
authors.forename: T
authors.initials: T
authors.lastname: Tkatch
authors.forename: D J
authors.initials: DJ
authors.lastname: Surmeier
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000502:physiology*; D002795:Choline O-Acetyltransferase / Q000235:genetics; D003342:Corpus Striatum / Q000502:physiology*; D005033:Ethylmaleimide / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010627:Phenethylamines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D020864:Calcium Channels, N-Type; D010627:Phenethylamines; D012333:RNA, Messenger; D018047:Receptors, Purinergic P1; D013873:Thionucleotides; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D006153:Guanosine Diphosphate; C053907:8-cyclopentyl-1,3-dimethylxanthine; C058394:2-chloro-N(6)cyclopentyladenosine; C023427:guanosine 5'-O-(2-thiodiphosphate); D013806:Theophylline; D002795:Choline O-Acetyltransferase; D019204:GTP-Binding Proteins; D000241:Adenosine; D005033:Ethylmaleimide