Beta-adrenergic modulation of barium currents and k+ contractures
in frog slow skeletal muscle fibers .
Huerta, Miguel, X[acute]ochitl Trujillo, and Clemente V[acute]asquez.
Centro Universitario de Investigaciones Biom[acute]edicas,
Universidad de Colima, Apartado Postal 11, Colima, Colima, 28000,
M[acute]exico
APStracts 3:0246C, 1996.
Beta-adrenergic modulation of the barium current (IBa) and K+
contracture in slow skeletal muscle fibers of the frog (Rana pipiens)
were investigated in intact fibers using 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 [mu]M) and a similar increased was observed with the
[beta]-specific agonist isoproterenol (1 [mu]M). Thus, the
epinephrine effect was mediated mainly by [beta]-adrenergic
receptors. External application of the permeable 8-Bromo cyclic AMP
(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 calcium
channels via cyclic AMP. 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 calcium channels to the
increase in tension is still not completely understood.
Received 26 March 1996; accepted in final form 23 July 1996.
APS Manuscript Number C173-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996