Delineation of endothelin receptors in human left ventricular smooth-muscle cells

Abstract

In the human heart, we have previously shown the predominance of endothelin (ET) ETA receptors, in addition to the presence of ET-1, ET-2, ET-3, and big ET-1. ET-1 is a potent constrictor of isolated epicardial coronary arteries, and this action is mediated via ETA receptors. To determine the source of ET in the heart, our aims were to obtain cell cultures from human left ventricle, identify the cell type, and characterize ET secretion and receptor expression. We explanted human left ventricular tissue. Positive staining with alpha-actin antibodies confirmed the presence of smooth-muscle cells, whereas negative staining for sarcomeric actin and von Willebrand factor indicated an absence of cardiac myocytes and endothelial cells, respectively. Therefore, the cultures were identified as human left ventricular smooth-muscle cells (HLVSMCs). Because blood vessels were not macroscopically visible in the ventricular tissue, the HLVSMCs most likely originated from intramyocardial resistance vessels. The cells secreted immunoreactive mature ET and big ET-1 (102 +/- 29 and 73 +/- 10 pM/24 h, respectively; mean of three individuals +/- SEM). Saturation binding studies showed that [125I]ET-1 bind with high affinity in this preparation (Kd 0.21 +/- 0.06 nM; Bmax 15 +/- 4 fmol/mg protein; mean of three individuals +/- SEM). A competition binding study using the ETA-selective antagonist FR139317 (10 pM-10 microM) revealed the predominance of ETA receptors (Kd 0.33 +/- 0.10 nM, n = 3). We have shown that smooth-muscle cells isolated from human left ventricle secrete immunoreactive mature ET and big ET-1, and express mainly ETA receptors. These cells may provide a useful model for studying the effects of ET in the regulation of vascular tone and of the blood supply in the myocardium.