title: Actions of isoproterenol in frog proximal tubules.
abstract: In the present work, we compared biochemical and electrophysiological actions of isoproterenol on frog proximal tubular cells by using tubule suspensions and giant entities obtained by cell fusion. Isoproterenol (ISO) dose-dependently stimulated cAMP production in tubule suspension and depolarized the "giant cell" membrane. Both effects were triggered by beta receptor occupancy, but strongly differed in their concentration-dependency, since depolarization occurred with an ISO concentration as low as 10(-12) mol/l whereas cAMP accumulation could be seen only with more than 10(-8) mol/l ISO. ISO-induced membrane depolarization was mimicked by forskolin which directly stimulated the catalytic subunit of adenylyl cyclase. In both isoproterenol- and forskolin-stimulated giant cells, membrane depolarization was accompanied by a decrease in membrane conductance, and both effects were inhibited by tetraethylammonium (TEA) and 4-aminopyridine (4-AP). On the other hand, ISO- and forskolin-induced cAMP production were not affected by TEA. The present data thus show that isoproterenol produces two independent effects in frog proximal tubule: it depolarizes the cell membrane by blocking a K+ conductance and activates adenylyl cyclase.
authors.affiliation: INSERM U323, Faculté de Médecine Necker-Enfants-Malades, Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Belachgar
authors.forename: F
authors.initials: F
authors.lastname: Discala-Blondeau
authors.forename: D
authors.initials: D
authors.lastname: Tondelier
authors.forename: M
authors.initials: M
authors.lastname: Baudouin-Legros
authors.forename: T
authors.initials: T
authors.lastname: Anagnostopoulos
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000526:Alprenolol / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002459:Cell Fusion; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D015726:Giant Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D011895:Rana ridibunda; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D013757:Tetraethylammonium Compounds; D005576:Colforsin; D019789:Tetraethylammonium; D000584:Amiloride; D000526:Alprenolol; D015761:4-Aminopyridine; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D011188:Potassium