Different effects of norepinephrine and KCl on the cytosolic Ca2+-tension relationship in vascular smooth muscle of rat aorta.

Norepinephrine and KCl induced a concentration-dependent increase in the cytosolic Ca2+ level [( Ca2+]cyt) measured either by intracellular fura 2-Ca2+ fluorescence or by 45Ca2+ uptake. Muscle contraction in isolated rat aortic strips was also increased although a greater contraction was induced by norepinephrine than by KCl at the same [Ca2+]cyt. This result suggests that the contraction of vascular smooth muscle is regulated by [Ca2+]cyt and also by other factor(s).