Dual Regulation of Kv1.2 Activation by PIP2

Abstract

Phosphatidylinositol (4,5)-bisphosphate is now recognized as a ubiquitous regulator of ion channels and transporters. We report here that PIP2 regulates activation of Kv1.2, a Shaker family voltage-gated potassium channel. In inside-out macropatches of Xenopus laevis oocytes, loss of PIP2 induced a leftward shift in the voltage-dependence of activation and a reduction in maximal current, which could be restored by exogenous PIP2 application. These findings were reproduced using the voltage-dependent lipid phosphatase Ci-VSP, which preferentially dephosphorylates PI(4,5)P2 to PI(4)P when activated by depolarization. The dual effect of PIP2 on the voltage-dependence of activation and current level exhibited distinct kinetics. The time course of PIP2 depletion (e.g. during rundown of activity) or recovery (e.g. upon re-phosphorylation of PI(4)P) indicated that the effect on the voltage-dependent shift proceeded with faster kinetics than the current level. Furthermore, high concentrations of diC8-PIP2, a soluble analog of PIP2, partially restored the shift in the voltage dependence of activation caused by PIP2 antibody but failed to do the same for the current level. Taken together, the two effects of PIP2 on the voltage-dependence of activation and the current level of Kv1.2 channels proceeded with distinct kinetics and sensitivity to PIP2, suggesting distinct underlying molecular determinants.