Differential effects of adenosine and nitroglycerin on the action potentials of large and small coronary arteries.

Abstract

Intracellular microelectrodes were used to study membrane electrical properties of isolated large (> 1.0 mm) and small (< 500 .mu.m) coronary arteries of the dog. The resting membrane potential (Em) was not significantly different in large arteries and small arteries (average of -56 mV and -53 mV, respectively) nor was the input resistance (9 M.OMEGA. and 10 M.OMEGA., respectively). Spontaneous action potentials were not present in vessels of either size, and action potentials could not be induced by electrical stimulation. Addition of tetraethylammonium ion (TEA, 10 mM) rapidly induced overshooting action potentials on electrical stimulation in both large and small arteries. The amplitude of the action potential increased as a function of log [Ca2+]o, the slope of the curve being 30 mV/decade in the large and small arteries, demonstrating that Ca2+ carries most of the inward current during the action potential. Verapamil (10-6 M) blocked these Ca2+-dependent action potentials in both the large and small coronaries. Adenosine (10-5 M) blocked the action potential in the small coronary arteries but had no effect on the action potential in the large coronary arteries. Nitroglycerin (10-5 M) blocked the action potential in the large coronary arteries but not in the small arteries. Adenosine blocks Ca2+ inward current preferentially in small coronary arteries and nitroglycerin blocks the Ca2+ current preferentially in large coronary arteries. These observations are consonant with a role for adenosine in the metabolic regulation of coronary blood flow in the small coronary vessels.