Caveolae are membrane domains thought to compartmentalize and/or sequester signalling molecules. In endothelial cells, they appear to be associated with initiation of Ca2+ waves. Following binding of ATP to Gq-coupled cell surface receptors, Ca2+ is released from the ER at sites associated with a subset of plasma membrane caveolae. Richard Anderson and co-workers have analysed the role of caveolae in Ca2+signalling in migrating endothelial cells. They show that cell migration induced by wounding or shear stress causes caveolae (but not clathrin-coated pits) to move to the trailing edge of the cell. The exciting finding is that this is accompanied by movement of both Ca2+-release sites and the G protein Gαq to the same location. Caveolae might thus act not only as containers for the Ca2+ signalling machinery but also as vehicles for its transport. If caveolae indeed function as transporters for signalling molecules, they could play a critical role in cell polarity.
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