Program in Neuroscience; Department of Physiology; Department of Biochemistry and Molecular Pharmacology
Animals; Animals, Newborn; Calcium Channel Blockers; Calcium Channels, L-Type; Cells, Cultured; Drug Interactions; Enzyme Inhibitors; Gas Chromatography-Mass Spectrometry; Immunohistochemistry; Membrane Potentials; Mice; Mice, Knockout; Neural Inhibition; Neurons; Patch-Clamp Techniques; Phospholipases A; Potassium Channel Blockers; Potassium Channels; RNA, Messenger; Rats; Rats, Sprague-Dawley; Receptor, Muscarinic M1; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Superior Cervical Ganglion
Life Sciences | Medicine and Health Sciences
Ion channels reside in a sea of phospholipids. During normal fluctuations in membrane potential and periods of modulation, lipids that directly associate with channel proteins influence gating by incompletely understood mechanisms. In one model, M(1)-muscarinic receptors (M(1)Rs) may inhibit both Ca(2+) (L- and N-) and K(+) (M-) currents by losing a putative interaction between channels and phosphatidylinositol-4,5-bisphosphate (PIP(2)). However, we found previously that M(1)R inhibition of N-current in superior cervical ganglion (SCG) neurons requires loss of PIP(2) and generation of a free fatty acid, probably arachidonic acid (AA) by phospholipase A(2) (PLA(2)). It is not known whether PLA(2) activity and AA also participate in L- and M-current modulation in SCG neurons. To test whether PLA(2) plays a similar role in M(1)R inhibition of L- and M-currents, we used several experimental approaches and found unanticipated divergent signaling. First, blocking resynthesis of PIP(2) minimized M-current recovery from inhibition, whereas L-current recovered normally. Second, L-current inhibition required group IVa PLA(2) [cytoplasmic PLA(2) (cPLA(2))], whereas M-current did not. Western blot and imaging studies confirmed acute activation of cPLA(2) by muscarinic stimulation. Third, in type IIa PLA(2) [secreted (sPLA(2))](-/-)/cPLA(2)(-/-) double-knock-out SCG neurons, muscarinic inhibition of L-current decreased. In contrast, M-current inhibition remained unaffected but recovery was impaired. Our results indicate that L-current is inhibited by a pathway previously shown to control M-current over-recovery after washout of muscarinic agonist. Our findings support a model of M(1)R-meditated channel modulation that broadens rather than restricts the roles of phospholipids and fatty acids in regulating ion channel activity.
DOI of Published Version
J Neurosci. 2006 Nov 8;26(45):11588-98. Link to article on publisher's site
The Journal of neuroscience : the official journal of the Society for Neuroscience
Liu, Liwang; Zhao, Rubing; Bai, Yan; Stanish, Lee F.; Evans, James E.; Sanderson, Michael J.; Bonventre, Joseph V.; and Rittenhouse, Ann R., "M1 muscarinic receptors inhibit L-type Ca2+ current and M-current by divergent signal transduction cascades" (2006). Open Access Articles. 1166.