Fig. 3.

Method for measurement of VSP activation in Xenopus oocytes. A: Schematic diagram of the surface of a Xenopus oocyte showing the plasma membrane containing PI(4,5)P₂, with the fluorescent sensor PLCδ1PH-GFP bound to it. The thick black band represents the layer of pigment granules underlying the plasma membrane. Application of blue light excites GFP, which emits green light. Activation of the VSP by membrane depolarization depletes PI(4,5)P₂, allowing PLCδ1PH-GFP to diffuse away from the membrane, such that its fluorescence is shielded by the pigment granules and yolk platelets in the oocyte cytoplasm. B: Electron micrograph showing the cortical structures in the black half of a Xenopus oocyte. MV, microvilli; CG, cortical granule; PG, pigment granule; YP, yolk platelet. The white areas are PGs and YPs that have been lost from the section. C: Photodiode measurement of PLCδ1PH-GFP emission from a voltage-clamped Xenopus oocyte.