Chloride equilibrium potential in salamander cones

Chloride equilibrium potential in salamander cones

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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 EMI Filter 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, Gloves 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).