Phosphotidylinositol 4,5-Bisphosphate Signals Underlie Receptor-Specific G _q/11-Mediated Modulation of N-Type Ca ²⁺ Channels

Abstract

Modulation of voltage-gated Ca ²⁺ channels via G-protein-coupled receptors is a prime mechanism regulating neurotransmitter release and synaptic plasticity. Despite extensive studies, the molecular mechanism underlying G _q/11-mediated modulation remains unclear. We found cloned and native N-type Ca ²⁺ channels to be regulated by phosphotidylinositol 4,5-bisphosphate (PIP ₂). In inside-out oocyte patches, PIP ₂ greatly attenuated or reversed the observed rundown of expressed channels. In sympathetic neurons, muscarinic M ₁ ACh receptor suppression of the Ca ²⁺ current ( I _Ca) was temporally correlated with PIP ₂ hydrolysis, blunted by PIP ₂ in whole-cell pipettes, attenuated by expression of PIP ₂-sequestering proteins, and became irreversible when PIP ₂ synthesis was blocked. We also probed mechanisms of receptor specificity. Although bradykinin also induced PIP ₂ hydrolysis, it did not inhibit I _Ca. However, bradykinin receptors became nearly as effective as M ₁ receptors when PIP ₂ synthesis, IP ₃ receptors, or the activity of neuronal Ca ²⁺ sensor-1 were blocked, suggesting that bradykinin receptor-induced intracellular Ca ²⁺ increases stimulate PIP ₂ synthesis, compensating for PIP ₂ hydrolysis. We suggest that differential use of PIP ₂ signals underlies specificity of G _q/11-coupled receptor actions on the channels.