Characterization of caveolae from rat heart: Localization of postreceptor signal transduction molecules and their rearrangement after norepinephrine stimulation

Caveolae are plasma membrane subcompartments that have been implicated in s ignal transduction. In many cellular systems, caveolae are rich in signal t ransduction molecules such as G proteins and receptor-associated tyrosine k inases. An important structural component of the caveolae is caveolin. Rece nt evidence show that among the caveolin gene family, caveolin-3 is express ed in skeletal and cardiac muscle and caveolae are present in cardiac myocy te cells. Both the ANP receptor as well as the muscarinic receptor have bee n localized to the caveolae of cardiac myocytes in culture. These findings prompted us to conduct a further analysis of cardiac caveolae. In order to improve our understanding of the mechanisms of signal transduction regulati on in cardiac myocytes, we isolated cardiac caveolae by discontinuous sucro se density gradient centrifugation from rat ventricles and rat neonatal car diocytes. Our analysis of caveolar content demonstrates that heterotrimeric G proteins, p21ras and receptor-associated tyrosine kinases are concentrat ed within these structures. We also show that adrenergic stimulation induce s an increase in the amount of diverse alpha- and beta-subunits of G protei ns, as well as p21ras, in both in vivo and in vitro experimental settings. Our data show that cardiac caveolae are an important site of signal transdu ction regulation. This finding suggests a potential role for these structur es in physiological and pathological states. J. Cell. Biochem. 77:529-539, 2000. (C) 2000 Wiley-Liss, Inc.