Phosphatidylinositol-4,5-bisphosphate-dependent Facilitation of the ATP-dependent Secretory Activity in Mouse Pituitary Cells
Phosphatidylinositol-4, 5-bisphosphate [PI(4,5)P2] has been implicated in the priming of large dense-core vesicles in many secretory cells; however, its role in the Ca2+-dependent secretory activity in pituitary cells remains elusive. We assessed the effect of elevated intracellular PI(4,5)P2 on the kinetics of Ca2+-dependent exocytosis, using a whole-cell patch-clamp technique in wild-type mouse melanotrophs from fresh pituitary tissue slices. We found that 1 ?mol/L PI(4,5)P2 significantly increased Ca2+-dependent exocytosis of vesicles that need to go through ATP-dependent reactions; however, the exocytosis of release-ready vesicles (ATP-independent release) and voltage-activated Ca2+ currents remained unaffected. We suggest that PI(4,5)P2 increases the size of the readily releasable vesicle pool by regulating the effectiveness of vesicular mobilization and fusion in an ATP-dependent manner.
pituitary priming ca2+-dependent exocytosis melanotrophs release-ready vesicles phosphatidylinositol-4 5-biphosphate capacitance measurements atp-independent pathway atp-dependent pathway acute tissue slices