Figure 5.
Rapid changes in the Kir current induced by VSP-catalyzed changes in PtdIns(4,5)P2. Shown are representative current traces with voltage steps recorded under two-electrode voltage clamp in a Xenopus oocyte co-expressing an isoform of the Kir3.2 channel (GIRK2d) with the G-protein β and γ subunits and Ci-VSP.50) The G-protein subunits are necessary for activation of the Kir3.2 channel. A hyperpolarizing step from a holding potential of −60 mV to −120 mV activated inward Kir currents. After an episode of depolarization to 100 mV for 1 s, which robustly activated Ci-VSP, PtdIns(4,5)P2 levels are decreased because VSP activity cleaves the 5-phosphate. This leads to a decrease in the Kir current in the second hyperpolarizing step. Endogenous outward currents are elicited during a depolarizing step to 100 mV.