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Synaptically Activated Low‐threshold Muscarinic Inward Current Sustains Tonic Firing in Rabbit Prevertebral Sympathetic Neurons
Author(s) -
Niel J.P.,
Delmas P.,
Gola M.
Publication year - 1996
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1996.tb01246.x
Subject(s) - tonic (physiology) , muscarinic acetylcholine receptor , neuroscience , rabbit (cipher) , chemistry , biophysics , biology , computer science , receptor , biochemistry , computer security
Whole‐cell patch‐clamp experiments were performed on non‐dissociated rabbit coeliac sympathetic neurons in the presence of nicotinic blockers. Coeliac neurons were classified as either silent or spontaneously active (pacemaker) cells. Under voltage‐clamp conditions, pacemaker cells exhibited a steady‐state N‐shaped current‐voltage relationship due to the presence of a persistent voltage‐dependent inward current in the potential range of ‐100 to —20 mV. This inward current sustained the regular firing activity of pacemaker cells and was absent from quiescent neurons. It disappeared in the presence of tetrodotoxin and in low Ca 2+ ‐high Mg 2+ external solutions and was enhanced by eserine. Splanchnic nerve stimulation induced slow regenerative depolarizations and firing discharges in silent neurons by activating a low‐threshold voltage‐sensitive inward current. The synaptic current had a U‐shaped voltage‐dependence from —96 to —20 mV and exhibited the dynamic properties of the muscarinic voltage‐dependent inward current l Na, M . It gave the current‐voltage relationship an N shape similar to that observed in spontaneously active cells. The muscarinic antagonists atropine and pirenzepine abolished the inward current present in pacemaker cells and that induced by nerve stimulation in silent neurons. These data provide evidence that both spontaneous firing activity and nerve‐evoked depolarizing responses in coeliac neurons are sustained by the activation of the muscarinic Na, M current. The tonic activation of l Na, M in spontaneously firing cells results from a sustained Ca 2+ ‐dependent tetrodotoxin‐sensitive release of acetylcholine. This study provides evidence that the role of the muscarinic receptors is not purely a neuromodulatory one, but that these receptors are directly involved in ganglionic neurotransmission.