Cytosolic calcium transients differ between porcine coronary arterial and aortic smooth muscle cells in primary culture

Abstract

Using quin 2 microfluorometry of porcine vascular smooth muscle cells in primary culture at 25°C, we investigated differences in cytosolic calcium transients between epicardial coronary artery and aorta. Both in coronary arterial and aortic smooth muscle cells, histamine induced transient and dose-dependent elevations of cytosolic calcium concentrations, with a similar time course and EC50 (coronary artery, 1.4 x 10-7 M; aorta, 1.8 x 10-7 M). However, a transient and dose-dependent elevation of cytosolic calcium concentrations was induced by norepinephrine in aortic smooth muscle cells (EC50 = 2.5 x 10-7 M) but not in coronary arterial smooth muscle cells. Isoproterenol, which produced no change in cytosolic calcium concentrations in aortic vascular smooth muscle cells, significantly and dose dependently decreased concentrations of calcium in coronary arterial smooth muscle cells (EC50 = 1.5 x 10-7 M). Dibutyryl cAMP decreased the concentration of cytosolic calcium both in the coronary arterial and aortic vascular smooth muscle cells with a similar time course and EC50 (coronary artery, 9.8 x 10-6 M; aorta, 1.1 x 10-5 M). Intracellular concentration of cAMP was increased in response to isoproterenol, as determined with radioimmunoassay of the coronary arterial smooth muscle cells but not in the aortic cells. Thus, the characteristics of receptors on the sarcolemma may play a key role in the regulation of responsiveness of vascular smooth muscle cells to various vasoactive substances. Aortic smooth muscle cells are α-receptor dominant, and activation results in a transient elevation of cytosolic calcium concentrations. The epicardial coronary arterial smooth muscle cells are β-receptor dominant, and activation results in an increase in cAMP and a reduction of cytosolic calcium concentrations. These results may account for the poor contraction, or relaxation, of epicardial coronary artery induced by sympathetic stimulation and exogenously applied catecholamines.