title: Adenosine inhibits calcium channel currents via A1 receptors on salamander retinal ganglion cells in a mini-slice preparation.
abstract: The effects of adenosine on high-voltage-activated calcium channel currents in tiger salamander retinal ganglion cells were investigated in a mini-slice preparation. Adenosine produced a concentration-dependent decrease in the amplitude of calcium channel current with a maximum inhibition of 26%. The effects of adenosine on calcium channel current were both time- and voltage-dependent. In cells dialyzed with GTP-gamma-s, adenosine caused a sustained and irreversible inhibition of calcium channel current, suggesting involvement of a GTP-binding protein. The inhibitory effect of adenosine on calcium channel current was blocked by the A1 antagonist 8-cyclopentyltheophylline (DPCPX, 1-10 microm), but not by the A2 antagonist 3-7-dimethyl-1-propargylxanthine (DMPX, 10 microm), and was mimicked by the A1 agonist N6-cyclohexyladenosine (CHA, 1 microm) but not by the A2 agonist 5'-(N-cyclopropyl) carbox-amidoadenosine (CPCA, 1 microm). Adenosine's inhibition of calcium channel current was not affected by the L-type calcium channel blocker nifedipine (5 microm). However, adenosine's inhibition of calcium channel current was reduced to approximately 10% after application of omega-conotoxin GVIA (1 microm), suggesting that adenosine inhibits N-type calcium channels. These results show that adenosine acts on an A1 adenosine receptor subtype via a G protein-coupled pathway to inhibit the component of calcium channel current carried in N-type calcium channels.
authors.affiliation: Departments of Anatomy and Neurobiology, Physiology and Biophysics and. Ophthalmology, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Sun
authors.forename: Steven
authors.initials: S
authors.lastname: Barnes
authors.forename: William H
authors.initials: WH
authors.lastname: Baldridge
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000557:Ambystoma; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism*; D003956:Dialysis; D005456:Fluorescent Dyes; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D018408:Patch-Clamp Techniques; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013805:Theobromine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D014970:Xanthines; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C057837:3,7-dimethyl-1-propargylxanthine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000241:Adenosine; D013805:Theobromine; D002118:Calcium