In cultured aortic smooth muscle cells, SHR cells show decreased endothelin-1 stimulated IP formation compared to WKY cells, but no alteration in pertussis toxin-sensitive G-protein coupling.
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Suggests blunted endothelin-1 signaling in hypertensive rat vessels without G-protein alteration; leaves open relevance to human hypertension mechanisms.
The effects of pertussis toxin on endothelin-1 and noradrenaline coupling to inositol phosphate (IP) formation was investigated in cultured aortic smooth muscle cells from 14 week SHR and WKY rats. Endothelin-1 (10(-6) M) stimulated IP formation was decreased in cells from SHR compared to WKY (WKY 1117 +/- 157, SHR 668 +/- 85% of basal). Pre-incubation with pertussis toxin produced a significant and similar reduction in endothelin stimulated IP production in both SHR (54% reduction) and WKY (55%). However, the observed reduction in endothelin-1 stimulated IP accumulation was still apparent in SHR when compared to WKY. Pertussis toxin preincubation followed by removal of extracellular calcium reduced further the endothelin responses by similar amounts in SHR and WKY cells, but SHR stimulated IP formation remained significantly decreased compared to WKY. The extent of pertussis toxin ADP-ribosylation of Gi alpha was similar in both SHR and WKY cells. Endothelin-1 produced a reduction in the extent of ADP-ribosylation of Gi alpha and this was of similar magnitude in both SHR and WKY cell membranes. In contrast, noradrenaline stimulated IP formation was unaffected by pertussis toxin pre-incubation. It was concluded that SHR cells do not appear to have an alteration in endothelin-1 activated, pertussis toxin sensitive G-protein coupling to IP formation or in the dependence of inositol phosphate formation on extracellular calcium.
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Nixon et al. (1995) studied this question.
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