title: A2 adenosine receptors inhibit calcium influx through L-type calcium channels in rod photoreceptors of the salamander retina.
abstract: Presynaptic inhibition is a major mechanism for regulating synaptic transmission in the CNS and adenosine inhibits Ca(2+) currents (I(Ca)) to reduce transmitter release at several synapses. Rod photoreceptors possess L-type Ca(2+) channels that regulate the release of L-glutamate. In the retina, adenosine is released in the dark when L-glutamate release is maximal. We tested whether adenosine inhibits I(Ca) and intracellular Ca(2+) increases in rod photoreceptors in retinal slice and isolated cell preparations. Adenosine inhibited both I(Ca) and the [Ca(2+)]i increase evoked by depolarization in a dose-dependent manner with approximately 25% inhibition at 50 microM. An A2-selective agonist, (N(6)-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl]adenosine) (DPMA), but not the A1- or A3-selective agonists, (R)-N(6)-(1-methyl-2-phenylethyl)adenosine and N(6)-2-(4-aminophenyl)ethyladenosine, also inhibited I(Ca) and depolarization-induced [Ca(2+)]i increases. An inhibitor of protein kinase A (PKA), Rp-cAMPS, blocked the effects of DPMA on both I(Ca) and the depolarization-evoked [Ca(2+)]i increase in rods. The results suggest that activation of A2 receptors stimulates PKA to inhibit L-type Ca(2+) channels in rods resulting in a decreased Ca(2+) influx that should suppress glutamate release.
authors.affiliation: Department of Pharmacology and Department of Ophthalmology, University of Nebraska Medical Center, Omaha, Nebraska 68198-5540, USA.
authors.forename: Salvatore L
authors.initials: SL
authors.lastname: Stella
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Bryson
authors.forename: Wallace B
authors.initials: WB
authors.lastname: Thoreson
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002469:Cell Separation; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014562:Caudata
chemical_list: D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; C086112:N(6)-2-(4-aminophenyl)ethyladenosine; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; C056426:CGS 24012; C047235:N-(1-methyl-2-phenylethyl)adenosine; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D000241:Adenosine; D011188:Potassium; D002118:Calcium