Relationship between contractile responses and cytosolic free calcium levels in response to phorbol ester (PMA) in isolated rat aorta.

We examined the relationship between phorbol ester (PMA)-induced contractile response and cytosolic free calcium level in the rat aorta. PMA (10(-6)M) produced biphasic contraction, i.e., sustained contraction followed by a phasic response superimposed on the sustained contraction. Increase in [Ca2+]i was accompanied by a phasic but not sustained contraction. These results suggest that PMA-induced phasic contraction is dependent on Ca2+ influx but sustained contraction may be due to an increase in Ca2+ sensitivity of contractile protein.