Citation

Group IVa cytosolic phospholipase A2 (cPLA2) mediates GPCR-stimulated arachidonic acid (AA) release from phosphatidylinositol 4,5-bisphosphate (PIP2) located in plasma membranes. We previously found in superior cervical ganglion (SCG) neurons that PLA2 activity is required for voltage-independent N-type Ca2+ (N-) current inhibition by M1 muscarinic receptors (M1Rs). These findings are at odds with an alternative model, previously observed for M-current inhibition, where PIP2 dissociation from channels and subsequent metabolism by phospholipase C suffices for current inhibition. To resolve cPLA2’s importance, we have investigated its role in mediating voltage-independent N-current inhibition (~40%) that follows application of the muscarinic agonist oxotremorine-M (Oxo-M). Preincubation with different cPLA2 antagonists or dialyzing cPLA2 antibodies into cells minimized N-current inhibition by Oxo-M, whereas antibodies to Ca2+-independent PLA2 had no effect. Taking a genetic approach, we found that SCG neurons from cPLA2-/- mice exhibited little N-current inhibition by Oxo-M, confirming a role for cPLA2. In contrast, cPLA2 antibodies or the absence of cPLA2 had no effect on voltage-dependent N-current inhibition by M2/M4Rs or on M-current inhibition by M1Rs. These findings document divergent M1R signaling mediating M-current and voltage-independent N-current inhibition. Moreover, these differences suggest that cPLA2 acts locally to metabolize PIP2 intimately associated with N- but not M-channels. To determine cPLA2’s functional importance more globally, we examined action potential firing of cPLA2+/+ and cPLA2-/- SCG neurons, and found decreased latency to first firing and interspike interval resulting in a doubling of firing frequency in cPLA2-/- neurons. These unanticipated findings identify cPLA2 as a tonic regulator of neuronal membrane excitability.