Slow cholinergic and peptidergic transmission in sympathetic ganglia.
Experiments of voltage-clamped bullfrog sympathetic neurons suggest that the "slow depolarization" produced by orthodromic stimulation, by muscarinic agonists, or by the peptide luteinizing hormone-releasing hormone (LHRH), results from the suppression of a time- and voltage-dependent outward K+ current, the "M current" (IM). This current is activated between -60 and -10mV, with a half-maximal activation voltage of -35 mV, a minimum time constant (TM) of 150 ms at -35 mV, and a voltage sensitivity corresponding to a single gating particle with a minimum valency of 4.IM does not show time-dependent inactivation within its activation range and provides the sole potential-sensitive component of the steady outward membrane conductances between -60 and -25 mV. Muscarinic agonists and LHRH selectively depress IM via different receptors, without altering their voltage sensitivity. Although not dependent on external Ca2+ ion, IM is also selectively depressed by Ba2+ ions, so accounting for the cholinomimetic action of Ba2+. It is suggested that IM acts as a braking control on spike discharges and that removal of this control during slow cholinergic and peptidergic transmission provides a unique synaptic tuning mechanism.
D000109:Acetylcholine / Q000502:physiology; D000818:Animals; D001464:Barium / Q000502:physiology; D005728:Ganglia, Sympathetic / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology; D011188:Potassium / Q000502:physiology; D011892:Rana catesbeiana; D011950:Receptors, Cholinergic / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission
D007473:Ion Channels; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D001464:Barium; D007987:Gonadotropin-Releasing Hormone; D000109:Acetylcholine; D011188:Potassium