Specific receptor for endothelin in cultured rat cardiocytes |
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Authors: | Y Hirata Y Fukuda H Yoshimi T Emori M Shichiri F Marumo |
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Institution: | Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan. |
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Abstract: | Specific binding sites for the endothelium-derived vasoconstrictor endothelin (ET) and its effect on cytosolic free Ca2+ concentrations ( Ca2+]i) were studied in a primary culture of cardiocytes from neonatal rats. Binding studies using 125I-labeled-porcine ET as a radioligand revealed the presence of a single class of high-affinity binding sites for ET in cardiocytes with an apparent Kd of 6-9 x 10(-10) M and a Bmax of 50,000-80,000 sites/cell. Neither various vasoconstrictors nor Ca2+-channel blockers affected the binding. Pretreatment with ET substantially reduced the total number of ET receptors without changing their affinity. ET dose-dependently increased Ca2+]i in fura-2-loaded cardiocytes. These data indicate that cardiocytes have specific ET receptors that are controlled by a down-regulation mechanism, and that ET induces a receptor-mediated increase in Ca2+]i in cardiocytes. |
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