Externalization of beta-adrenergic receptors promoted by myocardial ischemia.

beta-Adrenergic receptors were identified in two fractions of guinea pig myocardium: a purified sarcolemmal fraction and a light vesicle (presumably intracellular) fraction. In the light vesicle fraction, which contained approximately 25 percent of the myocardial receptors under control conditions, the receptors appeared to be segregated from the stimulatory guanine nucleotide binding and catalytic components of adenylate cyclase. During myocardial ischemia, beta-adrenergic receptors were redistributed from the intracellular vesicles to the sarcolemmal fraction, where isoproterenol-stimulated adenylate cyclase activity was increased. These findings should facilitate further studies on cellular and molecular mechanisms that regulate adrenergic receptor traffic in the myocardium and may explain the rapid enhancement in adrenergic receptor expression that occurs with myocardial ischemia.