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  • Title: Calcium dependence of effects of endothelin on rat mesenteric microvessels.
    Author: Deng LY, Schiffrin EL.
    Journal: Can J Physiol Pharmacol; 1991 Jun; 69(6):798-804. PubMed ID: 1913326.
    Abstract:
    We investigated the calcium dependence of the effects of endothelin (ET) on resistance vessels (less than 300 microns lumen diameter) from the mesenteric vascular bed of the rat, mounted on a wire myograph. ET-1 induced a potent sustained contraction with an ED50 of 12 nmol/L. The response to ET-3 and big ET at the maximum concentrations used (100 nmol/L) was less than 40% of that to ET-1, with an estimated ED50 of 45 nmol/L. Relaxation of the ET-1-induced contraction was slow, and resulted in a reduction of the maximum response to a second challenge with ET-1 to 60% of the initial contraction after 3 h. Long-lasting tachyphylaxis to arginine vasopressin (AVP) induced contraction also occurred. The response to 100 nmol/L ET-1 produced an active tension 88% greater than that induced by 124 mmol/L KCl, and similar to that produced by norepinephrine and AVP. The response to 100 nmol/L ET-1 in the absence of calcium + 1 mmol/L EGTA in the medium for 30 min resulted in a maximum contraction of 43% of the response in the presence of calcium, followed by a faster relaxation rate. The addition of calcium produced a further contraction, and stimulation with 100 nmol/L ET-1 at this point did not result in further response. The calcium channel blocker nitrendipine in concentrations of 1-10 mumol produced increasing reductions of the responses to 100 nmol/L ET-1 to 35% at the higher concentration. Nitrendipine (3 mumol/L) partially blocked the response to calcium after ET-1 was added in the absence of calcium.(ABSTRACT TRUNCATED AT 250 WORDS)
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