RT Journal Article SR Electronic T1 Functional Evidence of a Constitutively Active Population of α1D-Adrenoceptors in Rat Aorta JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 810 OP 817 VO 295 IS 2 A1 Regina Gisbert A1 Maria Antonia Noguera A1 Maria Dolores Ivorra A1 Pilar D'Ocon YR 2000 UL http://jpet.aspetjournals.org/content/295/2/810.abstract AB After depletion of intracellular calcium stores sensitive to noradrenaline, a spontaneous increase in the resting tone (IRT) when incubated in Ca2+-containing solution was observed in isolated rat aorta, but not in tail artery. This IRT does not depend on agonist activation of α1-adrenoceptors but it is inhibited by prazosin. A close relationship was found between the inhibitory potencies of prazosin (pIC50 = 9.833), BMY 7378 (pIC50 = 8.924), and 5-methylurapidil (pIC50 = 7.883) against IRT and their affinities for cloned α1D-adrenoceptors. Chloroethylclonidine (100 μmol · l−1) did not inhibit the IRT. After depletion of internal calcium stores by noradrenaline in absence of the agonist, loading in Ca2+-containing solution also brings about an increase in the inositol phosphate (IP) levels in rat aorta (not seen in tail artery) that is inhibited by prazosin (1 μmol · l−1), BMY 7378 (10 μmol · l−1), and 5-methylurapidil (10 μmol · l−1), thus confirming the results obtained in contractile studies. Chloroethylclonidine (100 μmol · l−1) did not inhibit this IP accumulation. The fact that the IRT and the IP accumulation related to it can be selectively inhibited by different α1-adrenoceptor antagonists suggests the existence of a population of α1D-adrenoceptors that show constitutive activity in rat aorta, not in tail artery. The American Society for Pharmacology and Experimental Therapeutics