title: Chloride equilibrium potential in salamander cones.
abstract: BACKGROUND
  GABAergic inhibition and effects of intracellular chloride ions on calcium channel activity have been proposed to regulate neurotransmission from photoreceptors. To assess the impact of these and other chloride-dependent mechanisms on release from cones, the chloride equilibrium potential (ECl) was determined in red-sensitive, large single cones from the tiger salamander retinal slice.
  
  
  RESULTS
  Whole cell recordings were done using gramicidin perforated patch techniques to maintain endogenous Cl- levels. Membrane potentials were corrected for liquid junction potentials. Cone resting potentials were found to average -46 mV. To measure ECl, we applied long depolarizing steps to activate the calcium-activated chloride current (ICl(Ca)) and then determined the reversal potential for the current component that was inhibited by the Cl- channel blocker, niflumic acid. With this method, ECl was found to average -46 mV. In a complementary approach, we used a Cl-sensitive dye, MEQ, to measure the Cl- flux produced by depolarization with elevated concentrations of K+. The membrane potentials produced by the various high K+ solutions were measured in separate current clamp experiments. Consistent with electrophysiological experiments, MEQ fluorescence measurements indicated that ECl was below -36 mV.
  
  
  CONCLUSIONS
  The results of this study indicate that ECl is close to the dark resting potential. This will minimize the impact of chloride-dependent presynaptic mechanisms in cone terminals involving GABAa receptors, glutamate transporters and ICl(Ca).
authors.affiliation: Department of Ophthalmology, University of Nebraska Medical Center, Omaha, NE, USA. wbthores@unmc.edu
authors.forename: Wallace B
authors.initials: WB
authors.lastname: Thoreson
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Bryson
mesh_terms: D000557:Ambystoma; D000818:Animals; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000502:physiology*
chemical_list: D018118:Chloride Channels; D002712:Chlorides