Chloride equilibrium potential in salamander cones

• Main Authors: Bryson Eric J, Thoreson Wallace B
• Format: Article
• Language: English
• Published: BMC 2004-12-01
• Series: BMC Neuroscience
• Online Access: http://www.biomedcentral.com/1471-2202/5/53

<p>Abstract</p> <p>Background</p> <p>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 (E_Cl) was determined in red-sensitive, large single cones from the tiger salamander retinal slice.</p> <p>Results</p> <p>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 E_Cl, we applied long depolarizing steps to activate the calcium-activated chloride current (I_Cl(Ca)) and then determined the reversal potential for the current component that was inhibited by the Cl^-channel blocker, niflumic acid. With this method, E_Clwas 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 E_Clwas below -36 mV.</p> <p>Conclusions</p> <p>The results of this study indicate that E_Clis close to the dark resting potential. This will minimize the impact of chloride-dependent presynaptic mechanisms in cone terminals involving GABA_areceptors, glutamate transporters and I_Cl(Ca).</p>