Arachidonic acid mediates muscarinic inhibition and enhancement of N-type Ca2+ current in sympathetic neurons.
N-type Ca(2+) channels participate in acute activity-dependent processes such as regulation of Ca(2+)-activated K(+) channels and in more prolonged events such as gene transcription and long-term depression. A slow postsynaptic M(1) muscarinic receptor-mediated modulation of N-type current in superior cervical ganglion neurons may be important in regulating these processes. This slow pathway inhibits N-type current by using a diffusible second messenger that has remained unidentified for more than a decade. Using whole-cell patch-clamp techniques, which isolate the slow pathway, we found that the muscarinic agonist oxotremorine methiodide not only inhibits currents at positive potentials but enhances N-type current at negative potentials. Enhancement was also observed in cell-attached patches. These findings provide evidence for N-type Ca(2+)-current enhancement by a classical neurotransmitter. Moreover, enhancement and inhibition of current by oxotremorine methiodide mimics modulation observed with direct application of a low concentration of arachidonic acid (AA). Although no transmitter has been reported to use AA as a second messenger to modulate any Ca(2+) current in either neuronal or nonneuronal cells, we nevertheless tested whether a fatty acid signaling cascade was involved. Blocking phospholipase C, phospholipase A(2), or AA but not AA metabolism minimized muscarinic modulation of N-type current, supporting the participation of these molecules in the slow pathway. A role for the G protein G(q) was also confirmed by blocking muscarinic modulation of Ca(2+) currents with anti-G(qalpha) antibody. Our finding that AA participates in the slow pathway strongly suggests that it may be the previously unknown diffusible second messenger.
Liu
Liwang
L
Program in Neuroscience, Department of Physiology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester 01655, USA.
Rittenhouse
Ann R
AR
D000818:Animals; D000831:Animals, Newborn; D016718:Arachidonic Acid / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009553:Nimodipine / Q000494:pharmacology; D010095:Oxotremorine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D017783:Superior Cervical Ganglion / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D018727:Muscarinic Antagonists; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; D016718:Arachidonic Acid; D009553:Nimodipine; D010095:Oxotremorine