| Research Abstract |
Aim of this project is to elucidate mechanism of vasoconstriction elicited by endothelin (ET). Since ET widely distributes in various tissues as well as in endothelium, elucidation of structure and function of ET-receptor is important. At the first step of this project, three distinct ET-isotypes were discovered. Subsequently, distribution of those isotypes in different tisuues was investigated. On the other hand, multiple functions of ET in various tissues were reported, suggesting the existence of subtypes of ET-receptor. We reported cDNA cloning of ET-receptor from rat lung and human jejunum cDNA libraries. As a result, those ET-receptors were classified into two subtypes, designated ETA and ETB. Both types belong to a type of receptor of seventurned G-protein coupled receptor. We made chimeric receptors of two subtypes of human ET-receptor and analyzed them with reference to structure-activity relationship. It was demonstrated that both types of the receptor activated by agonist, stimulate phosphoinositol turnover, to increase intracellular free calcium concentration. In addition, it was also demonstrated that, in various types of cell, ET stimulates opening of calcium channel and induces increase in calcium influx. Particularly in porcine coronary smooth muscle, voltage dependent calcium channel was opened by ET. This process is sensitive to pertussis toxin. Additionally, we demonstrated that vascular bed of spontaneous hypertensive rat is sensitive to ET. Causes of increase in the sensitivity to ET were analyzed and discussed. Further, we analyzed various pharmacological actions of ET in various tissues. Moreover, measurement of human plasma concentration of ET has added a great deal of clinical data regarding ET. Thus, research in this project has greatly progressed in accumulating knowledge of physiological and pathophysiological meaning of ET.
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