PI(4,5)P(2) regulates the gating of Na(V)1.4 channels

Voltage-gated sodium (Na(V)) channels are densely expressed in most excitable cells and activate in response to depolarization, causing a rapid influx of Na(+) ions that initiates the action potential. The voltage-dependent activation of Na(V) channels is followed almost instantaneously by fast inactivation, setting the refractory period of excitable tissues. The gating cycle of Na(V) channels is subject to tight regulation, with perturbations leading to a range of pathophysiological states. The gating properties of most ion channels are regulated by the membrane phospholipid, phosphatidylinositol (4,5) bisphosphate (PI(4,5)P(2)). However, it is not known whether PI(4,5)P(2) modulates the activity of Na(V) channels. Here, we utilize optogenetics to activate specific, membrane-associated phosphoinositide (PI)-phosphatases that dephosphorylate PI(4,5)P(2) while simultaneously recording Na(V)1.4 channel currents. We show that dephosphorylating PI(4,5)P(2) left-shifts the voltage-dependent gating of Na(V)1.4 to more hyperpolarized membrane potentials, augments the late current that persists after fast inactivation, and speeds the rate at which channels recover from fast inactivation. These effects are opposed by exogenous diC(8)PI(4,5)P(2). We provide evidence that PI(4,5)P(2) is a negative regulator that tunes the gating behavior of Na(V)1.4 channels.