title: Extracellular ATP activates calcium signaling, ion, and fluid transport in retinal pigment epithelium.
abstract: The presence of receptors for ATP has not been established in any native preparation of retinal neurons or glia. In the present study, we used conventional electrophysiological and [Ca2+]in fluorescence imaging techniques to investigate the effects of ATP added to Ringer's solution perfusing the retinal-facing (apical) membrane of freshly isolated monolayers of bovine retinal pigment epithelium (RPE). ATP (or UTP) produced large, biphasic voltage and resistance changes with a Kd of approximately 5 microM for ATP and approximately 1 microM for UTP. Electrical and pharmacological evidence indicates that the first and second phases of the response are attributable to an increase in basolateral membrane Cl conductance and a decrease in apical membrane K conductance, respectively. The ATP-induced responses were not affected by adenosine, but were reduced by the P2-purinoceptor blocker suramin. ATP also produced a large, transient increase in [Ca2+]in that was blocked by cyclopiazonic acid, an inhibitor of endoplasmic reticulum Ca2+-ATPases. The calcium buffer BAPTA attenuated the voltage effects of ATP. We also found that apical DIDS significantly inhibited the ATP-evoked [Ca2+]in and electrical responses, suggesting that DIDS blocked the purinoceptor. Measurements of fluid movement across the RPE using the capacitance probe technique demonstrated a significant increase in fluid absorption by apical UTP. These data indicate the presence of metabotropic P2Y/P2U-purinoceptors at the RPE apical membrane and implicate extracellular ATP in vivo as a retinal signaling molecule that could help regulate the hydration and chemical composition of the subretinal space.
authors.affiliation: School of Optometry and Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Peterson
authors.forename: C
authors.initials: C
authors.lastname: Meggyesy
authors.forename: K
authors.initials: K
authors.lastname: Yu
authors.forename: S S
authors.initials: SS
authors.lastname: Miller
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000241:Adenosine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000502:physiology*; D058914:Purinergic Antagonists; D011983:Receptors, Purinergic / Q000502:physiology; D015398:Signal Transduction; D013498:Suramin / Q000494:pharmacology; D013997:Time Factors; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D002614:Chelating Agents; D004791:Enzyme Inhibitors; D007211:Indoles; D058914:Purinergic Antagonists; D011983:Receptors, Purinergic; D001464:Barium; D004533:Egtazic Acid; D013498:Suramin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000241:Adenosine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium; D014544:Uridine Triphosphate; C000543:cyclopiazonic acid