Regulation of the subthreshold chloride conductance in the rat sympathetic neuron.
The mechanisms that control chloride conductance (gCl) in the rat sympathetic neuron have been studied by the two-electrode voltage-clamp technique in mature, intact superior cervical ganglia in vitro. In addition to voltage dependence in the membrane potential range -120/-50 mV, gCl displays time- and activity-dependent regulation (sensitization). The resting membrane potential is governed by voltage-dependent gK and gCl, which determine values of cell input conductance ranging from 7 to 18 nS (full deactivation) to an upper value of about 130 nS (full activation and maximal gCl sensitization). The quiescent neuron, held at constant membrane potential, spontaneously and gradually moved from a low- to a high-conductance status. An increase (about 40 nS) in gCl accounted for this phenomenon, which could be prevented by imposing intermittent hyperpolarizing episodes. Following spike firing, gCl increased by 20-33 nS, independent of the cell conductance value preceding tetanization, and thereafter decayed to the pre-stimulus level within 5 min. Intracellular sodium depletion and its successive ionophoretic restoration moved the neuron from a stable low-conductance state to maximum gCl sensitization, pointing to a link between gCl sensitization and [Na+]i. The dependence of gCl build-up on [Na+]i and the time-course of such Na+-related modulation have been examined: gCl sensitization was absent at 0 [Na+]i, was well developed (20 nS) at 15 mM and tended towards a saturating value of 60 nS for higher [Na+]i. Sensitization was transient in response to neuron activity. In the silent neuron, sensitization of gCl shifted membrane potential over a range of about 15 mV.
Sacchi
Oscar
O
Department of Biology, Section of Physiology and Biophysics and Center of Neuroscience, Ferrara University, Via Borsari, 46, I-44100 Ferrara, Italy. cho@unife.it
Rossi
Maria Lisa
ML
Canella
Rita
R
Fesce
Riccardo
R
D000818:Animals; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D002712:Chlorides / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D004553:Electric Conductivity; D004558:Electric Stimulation / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005665:Furosemide / Q000494:pharmacology; D066298:In Vitro Techniques; D017736:Ion-Selective Electrodes; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D017783:Superior Cervical Ganglion / Q000166:cytology*; D013997:Time Factors
D018118:Chloride Channels; D002712:Chlorides; D004791:Enzyme Inhibitors; D049994:Sodium Potassium Chloride Symporter Inhibitors; D010042:Ouabain; D005665:Furosemide