Intracellular signaling pathway of endothelin-1.
The intracellular signaling pathway of endothelin-1 (ET-1) was studied in individual mesangial cells (MCs) and vascular smooth muscle cells (VSMCs) using microspectrofluorimetry of fura-2 ([Ca2+]i), SPQ ([Cl-]i), and bisoxonol (membrane potential). ET-1 elicited a five-fold increase in [Ca2+]i that showed immediate and sustained phases. Both the Ca(2+)-free medium and nifedipine pretreatment curtailed the sustained phase of the response to ET-1. ET-1 resulted in sustained membrane depolarization of MCs and VSMCs. This depolarization was not attributed to Na influx, as Na-free medium did not abolish it. A Cl(-)-channel inhibitor, IAA-94, blunted the depolarization and sustained elevation of [Ca2+]i in response to ET-1. In aortic rings, both nifedipine and IAA-94 attenuated ET-1-induced contraction. No additivity in the effect of nifedipine and IAA-94 was detected. Studies of SPQ fluorescence changes induced by ET-1 revealed an immediate and sustained increase in fluorescence intensity consistent with the decrease in [Cl-]i. The sustained but not immediate increase in SPQ fluorescence was virtually abolished in Ca(2+)-free medium with or without pretreatment with the intracellular Ca2+ chelator BAPTA. In conclusion, we hypothesize that ET-1 results in Ca2+ mobilization and Ca(2+)-dependent and -independent activation of Cl- channels. Ensuing Cl- efflux causes membrane depolarization and, in turn, activation of voltage-gated Ca2+ channels in MCs and VSMCs. The latter results in sustained elevation of [Ca2+]i that is indispensable for the full-scale contractile response to ET-1.
Iijima
K
K
Department of Medicine, State University of New York, Stony Brook 11794-8152.
Lin
L
L
Nasjletti
A
A
Goligorsky
M S
MS
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D016232:Endothelins / Q000494:pharmacology*; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*
D015220:Calcium Channels; D002712:Chlorides; D016232:Endothelins; D002118:Calcium