A molecular sensor detects signal transduction from caveolae in living cells.

Biochemical and cell fractionation studies suggest caveolae contain functionally organized sets of signaling molecules that are capable of transmitting specific signals to the cell. It is not known, however, whether any signals actually originate from caveolae in living cells. To address this question, we have engineered the calcium sensor yellow cameleon so that it is targeted either to the plasma membrane, caveolae, or the cytoplasm of endothelial cells. Quantitative measurements of the three Ca2+ pools detected by these probes indicate that caveolae are preferred sites of Ca2+ entry when Ca2+ stores in the endoplasmic reticulum are depleted. These results suggest that the signaling machinery in control of Ca2+ entry is functionally organized in the caveolae of living cells.