Beta-adrenergic modulation of na/k pump activity in young and adult
canine cardiac purkinje fibers.
Charpentier, Flavien, Marianne J. Legato, Susan F. Steinberg, Ira S.
Cohen, Michael R. Rosen.
Departments of Pharmacology, Pediatrics, and Medicine, College of
Physicians and Surgeons of Columbia University, New York, New York,
Department of Physiology and Biophysics, SUNY Stony Brook, New
York
APStracts 2:0569H, 1995.
We used standard microelectrode techniques to study the developmental
changes and [beta]-adrenergic modulation of membrane potential and of
Na/K pump activity in adult (>1 year) and neonatal (2-10 days)
canine Purkinje fibers. Isoproterenol 10-7 M increased the rate of
development and magnitude of pacing-induced hyperpolarization of
adult fibers driven at a cycle length of 1 sec. This effect of
isoproterenol was attenuated by treating dogs with pertussis toxin
(PTX) (30 [mu]g/kg). Other adult and neonatal fibers were superfused
with a Tyrode's solution containing Ba2+ 0.2 mM, Cs+ 2 mM and
verapamil 10-6 M, leading to depolarization and cessation of
spontaneous activity. The Na/K pump was studied by alternating
solutions containing [K+] = 0 mM (inhibiting the pump) and 4 mM
(reactivating the pump). Although the kinetics of the Na/K pump
appeared faster in neonatal than adult fibers, measurement of cell
surface/volume ratio compensated for the difference. We therefore
conclude (1) the apparent age-related changes in Na/K pump activity
in canine Purkinje fibers in fact, reflect cell surface/volume ratio;
(2) the [beta]-adrenergic agonist-induced hyperpolarization in adults
requires the presence of a PTX-sensitive G-protein for its
occurrence.
Received 29 June 1995; accepted in final form 8 December 1995.
APS Manuscript Number H595-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95