Vascular smooth muscle: The first recorded Ca2+ transients

The bioluminescent calcium indicator aequor in was successfully loaded into vascular smooth muscle cells ofAmphiuma tridactylum by either microinjection or a new method which makes the cells reversibly hyperpermeable. Both gave similar results; however, the latter method produced larger signals. Vasoconstrictors produced a sustained contraction and a light (calcium) response consisting of two component: a large transient followed by a smaller, sustained response. Electrical stimulation produced a light transient that was much briefer than the contraction. These results suggest that tension can be maintained in smooth muscle in the presence of lower calcium levels than those present during force development.