Evidence for two separated Ca2+ pathways in smooth muscle plasmalemma.
The activation of rabbit aortic smooth muscle was studied by two most widely used vascular smooth muscle stimulants: alpha-adrenoceptor activation by norepinephrine (NE) and high-K+ depolarization. This was studied by measurements of isometric contractions and net as well as unidirectional Ca2+ fluxes. These parameters showed markedly differential sensitivities towards tow smooth muscle inhibitors used in this study: D600 and amrinone. By choosing an appropriate concentration of D600 or amrinone, Ca2+ uptake or Ca2+ influx induced by high K+ or NE could by selectively inhibited. Furthermore, by using unidirectional flux measurements it was demonstrated that Ca2+ influx stimulated by NE and high K+ were additive in nature. The data from the addivity experiment exclude the interpretation of a common Ca2+ pathway with two separate mechanisms for opening it. The data on three criteria employed in this study provide evidence for the existence of two independent Ca2+ pathways, one for each mode of activation, for Ca2+ influx known to be associated with these contractions.
D000631:Aminopyridines / Q000494:pharmacology; D000676:Amrinone; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002316:Cardiotonic Agents; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005711:Gallopamil / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits
D000631:Aminopyridines; D002316:Cardiotonic Agents; D005711:Gallopamil; D000676:Amrinone; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine