Adenosine receptor expression and modulation of Ca2+ channels in rat striatal cholinergic interneurons

Adenosine is a potent regulator of acetylcholine release in the striatum, y et the mechanisms mediating this regulation are largely undefined. To begin to fill this gap, adenosine receptor expression and coupling to voltage-de pendent Ca2+ channels were studied in cholinergic interneurons by combined whole cell voltage-clamp recording and single-cell reverse transcription-po lymerase chain reaction. Cholinergic interneurons were identified by the pr esence of choline acetyltransferase mRNA. Nearly all of these interneurons (90%, n = 28) expressed detectable levels of A, adenosine receptor mRNA. A, , and A(2b) receptor mRNAs were less frequently detected. A(3) receptor mRN A was undetectable. Adenosine rapidly and reversibly reduced N-type Ca2+ cu rrents in cholinergic interneurons. The A(1) receptor antagonist 8-cyclopen tyl-1,3-dimethylxanthine completely blocked the effect of adenosine. The IC 50 of the A, receptor selective agonist 2-chloro-N6-cyclopentyladenosine wa s 45 nM, whereas it was near 30 mu M for the A(2a) receptor agonist CGS-216 80. Dialysis with GDP beta S or brief exposure to the G protein (G(i/o)) al kylating agent N-ethylmaleimide also blocked the adenosine modulation. The reduction in N-type currents was partially reversed by depolarizing prepuls es. A membrane-delimited pathway mediated the modulation, because it was no t seen in cell-attached patches when agonist was applied to the bath. Activ ation of protein kinase C attenuated the adenosine modulation. Taken togeth er, our results argue that activation of A(1) adenosine receptors in cholin ergic interneurons reduces N-type Ca2+ 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.