PIP alters of Ca currents in acutely dissociated supraoptic oxytocin neurons.

Magnocellular neurosecretory cells (MNCs) occupying the supraoptic nucleus (SON) contain voltage-gated Ca channels that provide Ca for triggering vesicle release, initiating signaling pathways, and activating channels, such as the potassium channels underlying the afterhyperpolarization (AHP). Phosphotidylinositol 4,5-bisphosphate (PIP ) is a phospholipid membrane component that has been previously shown to modulate Ca channels, including in the SON in our previous work. In this study, we further investigated the ways in which PIP modulates these channels, and for the first time show how PIP modulates Ca channel currents in native membranes. Using whole cell patch clamp of genetically labeled dissociated neurons, we demonstrate that PIP depletion via wortmannin (0.5 μmol/L) inhibits Ca channel currents in OT but not VP neurons. Additionally, it hyperpolarizes voltage-dependent activation of the channels by ~5 mV while leaving the slope of activation unchanged, properties unaffected in VP neurons. We also identified key differences in baseline currents between the cell types, wherein VP whole cell Ca currents display more inactivation and shorter deactivation time constants. Wortmannin accelerates inactivation of Ca channels in OT neurons, which we show to be mostly an effect on N-type Ca channels. Finally, we demonstrate that wortmannin prevents prepulse-induced facilitation of peak Ca channel currents. We conclude that PIP is a modulator that enhances current through N-type channels. This has implications for the afterhyperpolarization (AHP) of OT neurons, as previous work from our laboratory demonstrated the AHP is inhibited by wortmannin, and that its primary activation is from intracellular Ca contributed by N-type channels.