Lead induces endothelium- and Ca2+-independent contraction in rat aortic rings

The contractile effect of lead on rat aortic rings was examined. Lead (0.1- 3.1 mM) elicited concentration-dependent but endothelium-independent contra ctions, which were unaffected by prazosin (1 muM), The contractile effects of lead were similar when the aortic rings were bathed either in the absenc e or presence of external Ca2+. Lanthanum (1 mM) but not verapamil (1 muM) inhibited the lead contractions; hence non-L-calcium channels are involved in such effect. In addition, lead induced contractions on aortic rings incu bated in Ca2+-free EGTA-containing solution for 70 min., an experimental co ndition in which intracellular Ca2+-stores are depleted. Finally, the contr actile effect of lead was not modified by calphostin C (an inhibitor of pro tein kinase C). In conclusion, the present results suggest that in rat aort a, the lead-induced contraction is independent of extra- and intracellular calcium stores. In addition, the effect of lead is independent of either ca techolamines or protein kinase C. It is likely that in rat aorta, lead ente rs into the smooth muscle cells through non-L-calcium channels, and when ac ting like calcium on the contractile machinery it produces contraction. The differences observed between our results and those obtained by other autho rs may indicate that the mechanism of the contractile effect of lead varies among the different blood vessels.