Which one the following does NOT primarily involve an action K+ channels?

Hypoxic pulmonary vasoconstriction and carotid body discharge are brought about by the O2-sensitive K+ channel. Insulin secretion by sulfonylurea is brought about by its action the ATP-sensitive K+ channel on the pancreatic b-cell. Malignant hypehermia is a disorder of excitation-contraction coupling, resulting from genetic defect of RyR (a Ca++-release channel). Dantrolene uncouples the excitation from contraction, by acting on the Ca++ channel.