Effect of membrane potential on H1-receptor-mediated 45Ca influx in coronary artery.
These studies were undertaken to determine whether agonist-induced 45Ca influx in the coronary artery is modified under conditions in which Na+ pump activity (and consequently membrane potential) is altered. 45Ca influx and contraction were measured in the rabbit coronary artery with the H1-receptor agonist 2-(2-aminoethyl)pyridine (AEP, 10(-4) M) after prolonged Na+ pump block (leading to profound depolarization) and after enhanced Na+ pump activity (leading to hyperpolarization). AEP contracted vessels, enhanced 45Ca influx into the smooth muscle, and increased 45Ca efflux. The AEP-induced contraction was reduced but not abolished with either nifedipine (10(-6) M) or Ca(2+)-free solution. In tissues subjected to prolonged Na+ pump block AEP caused contraction but 45Ca influx was not increased over the unstimulated tissue. Ca(2+)-free solution and nifedipine reduced but did not abolish these contractions. In tissues with enhanced Na+ pump activity AEP caused contraction but 45Ca influx was not increased. Ca(2+)-free solution reduced these contractions but nifedipine did not. We conclude that the measurable 45Ca influx changes in a manner that is compatible with the characteristics of voltage-gated Ca2+ channels that have a low open probability during hyperpolarization and are inactivated by a period of long slow depolarization.
Khoyi
M A
MA
Department of Pharmacology, University of Nevada, Reno 89557.
Bowen
S M
SM
Keef
K D
KD
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002132:Calcium Radioisotopes; D003331:Coronary Vessels / Q000378:metabolism / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials; D009543:Nifedipine / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D011969:Receptors, Histamine H1 / Q000502:physiology*; D015222:Sodium Channels / Q000378:metabolism / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects
D002132:Calcium Radioisotopes; D011725:Pyridines; D011969:Receptors, Histamine H1; D015222:Sodium Channels; C006183:2-(2-aminoethyl)pyridine; D009543:Nifedipine; D002118:Calcium