Beta-adrenergic modulation of Na-K pump activity in young and adult canine cardiac Purkinje fibers.
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 yr of age) 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 1-s cycle length. This effect of isoproterenol was attenuated by treating dogs with pertussis toxin (PTX), (30 micrograms/kg). Other adult and neonatal fibers were superfused with a Tyrode solution containing Ba2+ 0.2 mM, Cs+ 2 mM, and 10(-6) M verapamil, thus leading to depolarization and cessation of spontaneous activity. The Na-K pump was studied by alternating solutions containing [K] at 0 mM (inhibiting the pump) and 4 mM (reactivating the pump). Although the kinetics of the Na-K pump appeared faster in neonatal fibers than in adult fibers, measurement of cell surface-to-volume ratio compensated for the difference. We therefore conclude that 1) the apparent age-related changes in Na-K pump activity in canine Purkinje fibers in fact reflect cell surface-to-volume ratio and, 2) the beta-adrenergic agonist-induced hyperpolarization in adults requires the presence of a PTX-sensitive G protein for its occurrence.
Charpentier
F
F
Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York 10032, USA.
Legato
M J
MJ
Steinberg
S F
SF
Cohen
I S
IS
Rosen
M R
MR
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D004285:Dogs; D004594:Electrophysiology; D007545:Isoproterenol / Q000494:pharmacology*; D008954:Models, Biological; D037342:Pertussis Toxin; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects* / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol