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Fig. 2. Models for regulation of caveolar budding. Two non-exclusive models are presented. In A, there are two pools of caveolin-1-positive caveolae in the plasma membrane, one actively involved in budding/trafficking events whereas the other is essentially static. + denotes endocytically active pool of caveolae; – denotes inactive or static caveolae. How exchange between these pools might be regulated, and caveolar budding induced, is not known. Various possibilities are discussed in the text. In B, caveolar structures budding from the plasma membrane do not contain caveolin 1. How the rather uniform morphology and membrane curvature of these structures is then generated is not known, but further protein components may be involved. In this model, one function of caveolin 1 is to stabilize caveolar structures at the plasma membrane, preventing budding.
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