The Role of Intracellular Calcium Release in Norepinepherine-Induced Excitation/Contraction Coupling in Vascular Smooth Muscle
Mack, Christopher Paul
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The effects of intracellular calcium release on norepinepherine-induced contraction and receptor operated calcium channel sensitivity to the calcium antagonist diltiazem were studied in rabbit thoracic aortic artery. Contractions were elicited by agonist activation by norepinepherine (1 µM). Norepinepherine sensitive calcium release and influx were analyzed under the influence of the calcium release inhibitors, nicorandil and atriopeptin II. Pretreatments of nicorandil and atriopeptin lI on smooth muscle preparations showed inhibitory effects on calcium release as expected. Inhibition was also seen in calcium influx from the external medium. From these data a modulatory effect of calcium release on calcium influx is suggested. The effects of nicorandil and atriopeptin lI on the sensitivity of receptor operated calcium channels to diltiazem were examined. As inhibition of calcium release was increased by increasing concentrations of nicorandil and atriopeptin II, receptor operated calcium channel sensitivity to diltiazem was also increased. This indicates that calcium release is also involved in the activation of receptor operated channels. Studies were also performed to discover the importance of calcium release during NE activation. It was found that close to 50 percent of activating calcium enters the cell via the internal release pathway.