Phenotypic change of endothelin receptor subtype in cultured rat vascular smooth muscle cells

An endothelium-derived vasoactive peptide, endothelin (ET)-1, is a potent constrictor and mitogen for vascular smooth muscle cells (VSMC). To determine whether vascular ET receptor subtypes phenotypically change during in vitro culture conditions, we studied the expression of ET receptor subtypes, ET-induced phosphoinositide breakdown, and DNA synthesis in cultured rat VSMCs during serial passages. Binding studies using [125I]ET-1 as a radioligand revealed that the early passage (10th-15th) VSMCs possess predominantly ETA receptors, whereas the late passage (30th-35th) VSMCs possess predominantly ETB receptors in addition to ETA receptors. Northern blot analysis using cDNAs for rat ETA and ETB receptors as probes also demonstrated the predominant expression of ETA receptor mRNA in the early passage and ETB receptor mRNA in the late passage, whereas only ETA receptor mRNA was expressed in intact medium of rat aorta. ET-1 had a greater effect than ET-3 in stimulating inositol 1,4,5-trisphosphate formation, whereas ET-1 and ET-3 almost equipotently stimulated insitol 1,4,5-trisphosphate formation in the late passage VSMC even in the presence of an ETA receptor antagonist. ET-1-induced DNA synthesis was almost completely inhibited by an ETA receptor antagonist in the early passage VSMC. In contrast, ET-1, ET-3, and an ETB receptor agonist remarkably stimulated DNA synthesis in the late passage VSMC, which was completely inhibited by a nonselective ET receptor antagonist, but not by an ETA receptor antagonist. Our data provide the first evidence that a phenotypic change in VSMC in culture is concomitantly associated with a change in the ET receptor subtype that potentiates mitogenic activity and suggest that switching the ET receptor subtype from ETA to ETB during phenotypic change may in part contribute to the development of vascular lesions, such as in atherosclerosis.