Endothelin-induced increases in vascular smooth muscle Ca2+ do not depend on dihydropyridine-sensitive Ca2+ channels.
Endothelin is a potent mammalian vasoconstrictive peptide with structural homology to cation channel-binding insect toxins. We tested the proposal that this peptide directly activates dihydropyridine-sensitive Ca2+ channels in cultured vascular smooth muscle (VSM) cells. First, we found that cell Ca2+ can be altered in VSM by activation of voltage-operated Ca2+ channels. KCl-induced depolarization and the dihydropyridine Ca2+ channel agonist (-) Bay K 8644 (10 microM) both raised cell Ca2+ more than twofold; the effect of KCl was blocked by the inhibitory enantiomer, (+) Bay K 8644 (40 microM). Similar responses were observed in Chinese hamster ovary (CHO) cells. Synthetic endothelin (4 x 10(-8) M) raised Ca2+ in VSM but not CHO cells from 100 +/- 17 to 561 +/- 34 nM within 12 s. Ca2+ subsequently fell to basal levels after 30 min. Half maximal Ca2+ response was at 4 x 10(-9) M endothelin. Unlike endothelin, thrombin raised Ca2+ in both VSM and CHO cells. The Ca2+ responses to endothelin and thrombin were not affected by nicardipine (1 microM), (+) Bay K 8644, or Ca2+-free solutions. Lastly, both hormones caused release of inositol phosphates in VSM cells. However, the response to thrombin was more than 10-fold larger and was more rapid than the response to endothelin; the thrombin response was sensitive to pertussis toxin, while the response to endothelin was not. Thus endothelin, like thrombin, raises cell Ca2+ in VSM by mobilization of intracellular stores and not by activation of dihydropyridine-sensitive Ca2+ channels. However, their receptors are distinct and they exhibit important differences in signal transduction.
Mitsuhashi
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Cardiovascular Research Institute, University of California, San Francisco 94143.
Morris
R C
RC
Ives
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HE
D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D016232:Endothelins; D004730:Endothelium, Vascular / Q000502:physiology*; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000032:analysis / Q000187:drug effects*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction
D015220:Calcium Channels; D016232:Endothelins; D007295:Inositol Phosphates; D010455:Peptides; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium