Mesenteric vascular smooth muscle cells from spontaneously hypertensive rats display increased calcium responses to angiotensin II but not to endothelin-1

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Abstract
Objective To determine the differential calcium responses to two vasoconstrictor peptides, angiotensin II (Ang II) and endothelin-1, in vascular smooth muscle cells derived from mesenteric arteries from young and adult normotensive and hypertensive rats. Methods Effects of Ang II and endothelin-1 on cytosolic free calcium concentration in primary cultured unpassaged single vascular smooth muscle cells from mesenteric arteries of Wistar-Kyoto (WKY), Wistar and spontaneously hypertensive rats (SHR) aged 3, 9 and 17 weeks were examined microphotometrically using fura-2 methodology. Results Basal cytosolic free calcium concentration was significantly increased in cells from SHR aged 9 and 17 weeks compared with cells from age-matched WKY and Wistar rats. Ang II and endothelin-1 significantly increased cell cytosolic free calcium in all rat groups at all ages. Responses to low concentrations of Ang II (1 nmol/l) were significantly higher in cells from SHR aged 9 and 17 weeks than in age-matched controls. This was confirmed in cells from rats aged 17 weeks with full concentration-response curves, which also showed that the pD2 for Ang II for WKY rats was significantly different from that of SHR. In cells from SHR at all ages Ang II-stimulated cytosolic free calcium remained persistently high, whereas in cells from WKY and Wistar rats basal levels were reached within 100s after the maximal response. Low concentrations of endothelin-1 elicited significantly lower cytosolic free calcium responses in cells from SHR aged 17 weeks compared with age-matched controls. The time course of cytosolic free calcium responses to endothelin-1 were similar in the groups. Conclusions In primary cultured unpassaged mesenteric vascular smooth muscle cells from adult SHR, cytosolic free calcium concentration responses to Angll are enhanced, whereas responses to low concentrations of endothelin-1 are slightly reduced. The differential effects of these two vasoconstrictor peptides may contribute to their relative roles in modulating vascular smooth muscle cell cytosolic free calcium in SHR.

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