Phosphatidylinositol 4,5-bisphosphate optical uncaging potentiates exocytosis

Phosphatidylinositol-4,5-bisphosphate [PI(4,5)P(2)] is essential for exocytosis. Classical ways of manipulating PI(4,5)P(2) levels are slower than its metabolism, making it difficult to distinguish effects of PI(4,5)P(2) from those of its metabolites. We developed a membrane-permeant, photoactivatable PI(4,5)P(2), which is loaded into cells in an inactive form and activated by light, allowing sub-second increases in PI(4,5)P(2) levels. By combining this compound with electrophysiological measurements in mouse adrenal chromaffin cells, we show that PI(4,5)P(2) uncaging potentiates exocytosis and identify synaptotagmin-1 (the Ca(2+) sensor for exocytosis) and Munc13-2 (a vesicle priming protein) as the relevant effector proteins. PI(4,5)P(2) activation of exocytosis did not depend on the PI(4,5)P(2)-binding CAPS-proteins, suggesting that PI(4,5)P(2) uncaging may bypass CAPS-function. Finally, PI(4,5)P(2) uncaging triggered the rapid fusion of a subset of readily-releasable vesicles, revealing a rapid role of PI(4,5)P(2) in fusion triggering. Thus, optical uncaging of signaling lipids can uncover their rapid effects on cellular processes and identify lipid effectors.