Relaxation and polarization of precontracted rat aortic smooth muscle by sodium nitrite and an L-type channel blocker.

Unlabelled: Membrane potential (MP) is essential for smooth muscle (SM) contraction, mainly by determining the activity of L-type Ca2+ channels (Ca(L)). Although a widely used SM model, there are few electrophysiology studies in rat aorta.

Aim: We investigated the mechanism of SM relaxation induced by NaNO2 in comparison with a Ca(L) blocker.

Method: The dynamic MP-force relation was studied in de-endothelised rat aorta rings during contraction by 40 mM K+ or 0.01 mM phenylephrine (PHE) and relaxation by 0.01 mM methoxy-verapamil (D600) or 0.1 mM NaNO2.

Results: We confirm data on resting MP and depolarization by K+ or PHE. MP and Ca(L) are essential for K+ contraction and have little involvement in PHE contraction. NaNO2 polarization is not positively correlated with the relaxing effect.

Conclusions: Our studies on the MP-force relation provide novel information regarding the excitation-contraction coupling in SM. Polarization seems to be just an additional mechanism within nitrite-induced relaxation and may not involve K+ channel activation.