CAVEOLAE FROM LUMINAL PLASMALEMMA OF RAT LUNG ENDOTHELIUM - MICRODOMAINS ENRICHED IN CAVEOLIN, CA2-ATPASE, AND INOSITOL TRISPHOSPHATE RECEPTOR()

A distinctive feature of many endothelia is an abundant population of noncoated plasmalemmal vesicles, or caveolae, Caveolae have been impli cated in many important cellular processes, including transcytosis, en docytosis, potocytosis, and even signal transduction, Because caveolae have not been purified from endothelial cell surfaces, little is know n directly about their structure and function in the endothelium. To d elineate the transport role of these caveolae, we purified them from i solated luminal endothelial plasma membranes of rat lung, The rat lung luminal endothelial cell surfaces were isolated after coating them, i n situ, with positively charged colloidal silica. The caveolae were th en separated from these coated membranes and purified to yield a homog eneous population of morphologically distinct vesicles enriched in the structural protein caveolin, As with caveolae found on the endothelia l cell surface in vivo, these highly purified caveolae contained the p lasmalemmal Ca2+-ATPase and inositol 1,4,5-trisphosphate surface recep tors, By contrast, other plasma membrane proteins were excluded from t he caveolae, including angiotensin-converting enzyme, beta-actin, and band 4.1, The purified caveolae appeared to represent specific microdo mains of the cell surface with their own unique molecular topography.