beta-Adrenergic modulation of Ba2+ currents and K+ contractures in frog slow skeletal muscle fibers.
beta-Adrenergic modulation of the Ba2+ current (IBa) and K+ contracture in slow skeletal muscle fibers of the frog (Rana pipiens) were investigated in intact fibers with the three-microelectrode voltage-clamp technique and isometric tension measurements. Application of epinephrine (10(-6) to 10(-5) M) to the bath increased the amplitude of IBa. This increase was blocked by the beta-antagonist propranolol (3 microM), and a similar increase was observed with the beta-specific agonist isoproterenol (1 microM). Thus the epinephrine effect was mediated mainly by beta-adrenergic receptors. External application of permeable 8-bromoadenosine 3',5'-cyclic monophosphate (0.5 mM) increased the amplitude of both IBa and K+ contractures. The present results suggest that beta-adrenergic modulation of IBa in slow skeletal muscle fibers could reflect a modulation of Ca2+ channels via adenosine 3',5'-cyclic monophosphate (cAMP). cAMP (0.5 mM) also potentiated the K(+)-evoked tension in these slow fibers. The physiological contribution made by the modulation of slow skeletal muscle Ca2+ channels to the increase in tension is still not completely understood.
Huerta
M
M
Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Mexico.
Trujillo
X
X
Vásquez
C
C
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D004553:Electric Conductivity; D004837:Epinephrine / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D009119:Muscle Contraction; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D011894:Rana pipiens; D011943:Receptors, Adrenergic, beta / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D001464:Barium; D000242:Cyclic AMP; D007545:Isoproterenol; D011188:Potassium; D004837:Epinephrine