Modulating Modulation: Crosstalk Between Regulatory Pathways of Presynaptic Calcium Channels

Abstract

The activity of some voltage-gated calcium channels (VGCCs) can be inhibited by specific G protein β subunits. Conversely, in the case of N-type VGCCs, protein kinase C can relieve G_β-dependent inhibition by phosphorylating at least one specific site on the calcium channel. A recent publication describes a newly identified method of intracellular regulation of specific VGCCs. Wu et al. have uncovered that VGCC activity can be regulated by phosphatidylinositol-4′,5′-bisphosphate (PIP₂ ). Whereas PIP₂ is important for maintaining the activity (open state) of Ca_v2.1 (N-type) and Ca_v2.2 (P/Q-type) channels, the enzymatic breakdown of PIP₂ leads to the inactivation of these channels. Additionally, PIP₂ can cause changes in voltage-dependent activation of Ca_v2.2 (P/Q-type) channels that make it more difficult for these channels to open (from the closed state). Furthermore, protein kinase A activity can circumvent PIP₂-mediated inhibition. Thus, the PIP₂-mediated regulation of VGCCs is tightly controlled by the functions of kinases (and phosphatases), as well as phospholipases. Wu et al. stress that because PIP₂ can be found at synapses, PIP₂-dependent control of VGCCs “could have profound consequences on synaptic transmission and plasticity.”