The proposed research is designed to investigate the biochemical basis of the diminished beta adrenergic responsiveness induced by volatile anesthetics in the heart. The major hypothesis to be tested is that volatile anesthetics, (e.g., halothane, isoflurane) alter the functional state of the G proteins that regulate the beta adrenergic receptor stimulation of adenylate cyclase. Experiments are designed to identify changes in G protein associated with the anesthetic-induced decrease in adenylate cyclase activity; to determine whether volatile anesthetics alter the accessibility of the G protein or its availability, i.e. distribution between plasma membrane, sarcoplasmic reticulum and cytosol; to evaluate the influence of the membrane structure and of cellular components in the action of volatile anesthetics. Three preparations from rat heart will be used: membranes from myocardium of rats exposed to volatile anesthetics, from disaggregated cardiomyocytes exposed to the anesthetics, and membranes, prepared from myocardium of naive rats, exposed in vitro to the anesthetics. These three preparations will permit an analysis of the changes in G protein which relate to a direct effect of the anesthetic on the myocyte, as well as to the physiologic response of the animal to the anesthetic. Our approach to determine the functional state of G protein will include toxin-catalyzed ADP- ribosylation, immunochemical analysis, and cyc reconstitution assay. G proteins play a pivotal role in signal transduction and a change in their functional state has been implicated in certain cardiovascular or other pathological disorders. Thus an interaction of volatile anesthetics with G proteins may explain the change in anesthetic sensitivity in patients receiving certain medication pre- or intraoperatively, or in pathological conditions associated with altered G protein function. Since it is an accepted concept that a generalized disturbance of signal transduction in the CNS underlies the state of anesthesia, the results of these studies, obtained in a simple model, may also be of relevance towards an understanding of the biochemical basis of the state of aesthesia.