Caveolae in human and murine osteoblasts

Caveolae are 50- to 100-nm plasmalemmal vesicles formed by oligomerized cav eolin, a 22-kDa phosphoprotein, These organelles have been implicated in cr itical signal transduction and molecular transport processes. Here, we show for the first time that osteoblasts express caveolin and have abundant cav eolae, Membrane fractionation techniques indicate that osteoblast caveolin is found in detergent-resistant membranes that have the buoyant density cha racteristic of caveolae, whereas immunoblotting and reverse-transcription p olymerase chain reaction (RT-PCR) show that osteoblasts express both caveol in-1 and -2 isoforms, Electron microscopy (EM) and immunofluorescence revea l the hallmarks of caveolae in osteoblasts: abundant 50- to 100-nm noncoate d cell surface invaginations (caveolae) and abundant punctate clusters of i mmunostained caveolin.