title: A2 adenosine receptors in Mongolian gerbil middle ear epithelium and their regulation of Cl- secretion.
abstract: The present study investigates the effects of adenosine and its analogues on Cl- secretion in primary cultures of gerbil middle ear epithelium. Short-circuit current (Isc), an index of transepithelial active transport, was measured on the same cells cultured on porous filters. Baseline Isc and transepithelial resistance were 27.0 +/- 0.7 microA cm-2 and 275 +/- 7 omega cm2, respectively (n = 178). Extracellular adenosine and its analogues elicited a sustained increase in Isc when added to apical or basolateral surfaces. Both the A2A selective agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido adenosine and the A2A/A2B nonselective agonist 5'-(N-ethyl-carboxamido)adenosine (NECA) increased Isc, but NECA was more effective than CGS21680. A1 selective antagonist 8-cyclopentyl-1,3-dipropylxanthine did not reduce NECA-induced Isc. These results suggest the presence of both A2A and A2B receptors. NECA did not stimulate a rise in the intracellular Ca2+ concentration ([Ca2+]i) in single middle ear epithelial cells cultured on glass coverslips. Dibutyryl cAMP (dbcAMP) induced an initial transient increase in Isc followed by the sustained plateau. Addition of dbcAMP also caused a transient increase in [Ca2+]i. The protein kinase A inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide, greatly reduced the increase in the Isc responses to NECA. 1,2-Bis-(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid-acetoxymethyl ester influenced neither the NECA-induced increase in Isc nor the dbcAMP-induced sustained phase of Isc, but greatly inhibited the dbcAMP-induced transient increase in Isc. Glibenclamide, a cystic fibrosis transmembrane conductance regulator (CFTR) channel inhibitor, reduced the NECA-induced Isc. These results indicate that extracellular adenosine and its analogues activate the cAMP-protein kinase A system, but not intracellular Ca(2+)-dependent mechanisms, leading to Cl- secretion, possibly through the CFTR Cl- channels in the cultured gerbil middle ear epithelium.
authors.affiliation: Department of Otorhinolaryngology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Furukawa
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.forename: T
authors.initials: T
authors.lastname: Oshima
authors.forename: H
authors.initials: H
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Yamaya
authors.forename: H
authors.initials: H
authors.lastname: Sasaki
authors.forename: T
authors.initials: T
authors.lastname: Takasaka
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004432:Ear, Middle / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D017097:Electric Impedance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D018047:Receptors, Purinergic P1 / Q000378:metabolism / Q000502:physiology*
chemical_list: D002614:Chelating Agents; D002712:Chlorides; D004791:Enzyme Inhibitors; D018047:Receptors, Purinergic P1; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D019830:Adenosine-5'-(N-ethylcarboxamide); D004533:Egtazic Acid; D003994:Bucladesine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000241:Adenosine; D002118:Calcium