Membrane potential (MP) is essential in smooth muscle (SM) contractile activity, mainly by its effect upon L-type Ca2+ channels. We simultaneously recorded SM isometric tension and MP in de-endothelised rat aorta rings and examined their submaximal activation by K+, norepinephrine (NE) or phenylephrine (PHE) and the influence of methoxyverapamil (D600). K+ -induced contraction strictly correlated with depolarization, while faster contractions induced by NE or PHE started and peaked with a less depolarized membrane. D600 completely relaxed K+ or NE contracted rings, time-correlated with full repolarization, but partially relaxed PHE-contracted rings, with partial repolarization, which did not precede relaxation. The observed MP and force dynamics support known mechanisms of action of the drugs used. L-type channels participate in the depolarizing and contractile effect of NE, as opposite to their minor involvement in the effects of PHE.