A simple procedure for assessing norepinephrine-induced cellular and extracellular Ca++ mobilization in rabbit ear artery.

Although the response of vascular smooth muscle to norepinephrine (NE) is biphasic in nature, there is no simple procedure for the separate quantitative analysis of intracellular and extracellular Ca++ dependent NE-induced contractions. Intraluminal NE in high-K+Ca++-free medium produces a dose-dependent contraction which is selectively antagonized by procaine (1 X 10(-3) M--5 X 10(-3) M). Subsequent reperfusion with normal Krebs of NE-pretreated arterial segments results in a dose-dependent contraction which is strictly related to extracellular Ca++ concentration and is selectively inhibited by verapamil (5 X 10(-6) M--5 X 10(-5) M). These results can be interpreted as an indication that this procedure is suitable for the separate analysis of the capability of vasoactive drugs to differentially mobilize cellular and extracellular Ca++ pools in perfused rabbit ear artery preparations.