Identification of the receptor subtype responsible for endothelin-mediated protein kinase C activation and atrial natriuretic factor secretion from atrial myocytes.
Endothelin-1 (ET-1) is a potent stimulator of atrial natriuretic factor (ANF) secretion from myocardial cells. In heart tissue there are two ET receptor subtypes (ETA-R and ETB-R), which can be pharmacologically distinguished by the ET isopeptides ET-1 and ET-3. However, the identification of the ET-R subtype responsible for the rapid enhancement of ANF release, which occurs within minutes of exposing cardiac myocytes to ET, has not been investigated. In the present study ET-1 was about 100-fold more potent than ET-3 at stimulating membrane phosphoinositide hydrolysis, protein kinase C activation, and ANF release from purified primary atrial myocytes. These responses were completely abolished by BQ123, an ETA-R antagonist. Radioligand binding analyses showed that competitor peptides displaced 125I-ET-1 binding to atrial myocyte ET-Rs with a rank order of potency of ET-1 >> BQ123 > ET-3, a characteristic ETA-R pharmacological profile. While neither ET-1 or ET-3 altered forskolin-stimulated cAMP levels, suggesting the absence of the ETB-R, basal cAMP levels were also unaffected by the ETs. Northern analysis using ET-R subtype-specific probes demonstrated that the ETA-R transcript was present in the cultures at levels at least 50-fold greater than the ETB-R transcript. These findings demonstrate that the stimulation of the phosphatidylinositol/protein kinase C pathway, which is required for maximal ET-stimulated ANF release from primary atrial myocytes, is associated with the activation of only the ETA-R, thus defining a specific function for an endogenous ET-R in myocardial cells.
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Department of Biology, San Diego State University, California 92182.
Murray
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Glembotski
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D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D001483:Base Sequence; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D016232:Endothelins / Q000145:classification / Q000494:pharmacology*; D004789:Enzyme Activation; D015870:Gene Expression; D006325:Heart Atria / Q000378:metabolism*; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010456:Peptides, Cyclic / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017466:Receptors, Endothelin / Q000378:metabolism*
D016232:Endothelins; D007295:Inositol Phosphates; D009838:Oligodeoxyribonucleotides; D010456:Peptides, Cyclic; D012333:RNA, Messenger; D017466:Receptors, Endothelin; D005576:Colforsin; D009320:Atrial Natriuretic Factor; D000242:Cyclic AMP; D011493:Protein Kinase C; C072247:cyclo(Trp-Asp-Pro-Val-Leu)