Many important cellular functions are regulated by vascular potassium channels, including the resting membrane potential. Recent evidence suggests that the function of these channels is altered in pathophysiological disorders of the cardiovascular system. Using molecular cloning techniques, considerable effort has been made over the past 5 years to elucidate the structure of various types of potassium channels. Several different potassium channel clones have been identified from neuronal and cardiac tissues, although only a few have so far been identified in smooth muscle.