Cromakalim (INN) is a potassium channel-opening vasodilator. The active isomer is levcromakalim. It acts on ATP-sensitive potassium channels and so causes membrane hyperpolarization. It can be used to treat hypertension as it will relax vascular smooth muscle to lower blood pressure. Hyperpolarisation of smooth muscle cell membranes pulls their membrane potential away from the threshold, so making it more difficult to excite them and thereby cause contraction.