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Nature. 1994 Apr 28;368(6474):850-3.

Nitric oxide directly activates calcium-dependent potassium channels in vascular smooth muscle.

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Robert Dawson Evans Department of Clinical Research, Boston University Medical Center, Massachusetts 02118.


Nitric oxide is the major endothelium-derived relaxing factor (EDRF), and it is thought to relax smooth muscle cells by stimulation of guanylate cyclase, accumulation of its product cyclic GMP, and cGMP-dependent modification of several intracellular processes, including activation of potassium channels through cGMP-dependent protein kinase. Here we present evidence that both exogenous nitric oxide and native EDRF can directly activate single Ca(2+)-dependent K+ channels (K+Ca) in cell-free membrane patches without requiring cGMP. Under conditions when guanylate cyclase was inhibited by methylene blue, considerable relaxation of rabbit aorta to nitric oxide persisted which was blocked by charybdotoxin, a specific inhibitor of K+Ca channels. These studies demonstrate a novel direct action of nitric oxide on K+Ca channels.

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