title: Calcium-dependent, iproveratril-resistant contractions of aortic strips induced by a convulsant barbiturate.
abstract: At 3 X 10(-5) M concentratons, 5-(2-cyclohexylideneëthyl)-5-ethyl barbituric acid (CHEB) causes a contraction of rabbit aortic strips that is equivalent to about half of the maximal response to norepinephrine. If a calcium-free medium is substituted for normal bathing solution and drug is added immediately thereafter, there is no response to the convulsant barbiturate but a nearly normal response to norepinephrine. When calcium is replaced in stepwise increments, the contractor response to CHEB appears in corresponding increments. The prompt influence of changes in external calcium-concentration suggests that CHEB-induced contraction occurs as a result of calcium influx into cells rather than a release of free calcium from previously accumulated intracellular stores. CHEB effect, like that of potassium, is prevented by pretreatment with lanthanum (5 X 10(-3)M). CHEB differs from potassium in that its effects are even more sensitive to changes in extracellular calcium concentration. Nevertheless, CHEB can contract aortic strips in the presence of iproveratril at a concentration (10(-4)M) that blocks all response to potassium (100 mM).
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects; D001463:Barbiturates / Q000494:pharmacology*; D002118:Calcium / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D003292:Convulsants / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D013618:Tachyphylaxis; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D001463:Barbiturates; D003292:Convulsants; D014700:Verapamil; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine