Caveolae can be alternative endocytotic structures in elicited macrophages.

The aim of the present study was to identify omega-shaped plasma membrane invaginations, abundantly present in the plasma membrane of elicited macrophages, as caveolae. We have used an antibody against the major component of the caveolar coat (VIP21/caveolin), and the omega-shaped vesicles were found to be labeled with anti-VIP21 providing evidence that these structures were really caveolae. Filipin that had been shown to affect caveolae was used to investigate the possible endocytotic role of these structures in elicited macrophages. When caveolae were selectively inhibited by filipin, the rate of both fluid-phase and receptor-mediated endocytosis has been decreased. These data together with our results obtained from serial sectioning support that in elicited macrophages caveolae can pinch off from the plasma membrane and can function as alternative carriers in the endocytotic processes of these cells.