cPLA.sub.2[alpha].sup.-/- sympathetic neurons exhibit increased membrane excitability and loss of N-Type Ca.sup.2+ current inhibition by M.sub.1 muscarinic receptor signaling

• Published in: PloS one 2018-12, Vol.13 (12), p.e0201322
• Main Authors: Liu, Liwang, Bonventre, Joseph V, Rittenhouse, Ann R
• Format: Article
• Language: English
• Subjects: Cell membranes; Cellular signal transduction; Health aspects; Laboratory rats; Muscarinic receptors
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0201322

Group IVa cytosolic phospholipase A.sub.2 (cPLA.sub.2 [alpha]) mediates GPCR-stimulated arachidonic acid (AA) release from phosphatidylinositol 4,5-bisphosphate (PIP.sub.2) located in plasma membranes. We previously found in superior cervical ganglion (SCG) neurons that PLA.sub.2 activity is required for voltage-independent N-type Ca.sup.2+ (N-) current inhibition by M.sub.1 muscarinic receptors (M.sub.1 Rs). These findings are at odds with an alternative model, previously observed for M-current inhibition, where PIP.sub.2 dissociation from channels and subsequent metabolism by phospholipase C suffices for current inhibition. To resolve cPLA.sub.2 [alpha]'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 cPLA.sub.2 [alpha] antagonists or dialyzing cPLA.sub.2 [alpha] antibodies into cells minimized N-current inhibition by Oxo-M, whereas antibodies to Ca.sup.2+ -independent PLA.sub.2 had no effect. Taking a genetic approach, we found that SCG neurons from cPLA.sub.2 [alpha].sup.-/- mice exhibited little N-current inhibition by Oxo-M, confirming a role for cPLA.sub.2 [alpha]. In contrast, cPLA.sub.2 [alpha] antibodies or the absence of cPLA.sub.2 [alpha] had no effect on voltage-dependent N-current inhibition by M.sub.2 /M.sub.4 Rs or on M-current inhibition by M.sub.1 Rs. These findings document divergent M.sub.1 R signaling mediating M-current and voltage-independent N-current inhibition. Moreover, these differences suggest that cPLA.sub.2 [alpha] acts locally to metabolize PIP.sub.2 intimately associated with N- but not M-channels. To determine cPLA.sub.2 [alpha]'s functional importance more globally, we examined action potential firing of cPLA.sub.2 [alpha].sup.+/+ and cPLA.sub.2 [alpha].sup.-/- SCG neurons, and found decreased latency to first firing and interspike interval resulting in a doubling of firing frequency in cPLA.sub.2 [alpha].sup.-/- neurons. These unanticipated findings identify cPLA.sub.2 [alpha] as a tonic regulator of neuronal membrane excitability.