Activation by methylene blue of large Ca(2+)-activated K+ channels.

Using the patch-clamp method, we found that methylene blue (MB), a free radical inhibitor of guanylyl cyclase, activated large, Ca(2+)-activated K+ channels (BKCa) in either cell attached or excised, inside-out patches of human mesangial cells in culture. Since BKCa are important feedback regulators of contraction of smooth muscle and mesangial cells, these results indicate that MB may be an important opener of BKCa channels and a regulator of vascular volume and resistance.