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P. De la Villa, C. Varela, L. Rivera, R. Blanco; Gaba-induced Depolarization in Horizontal Cells of the Mammalian Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2006.
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Purpose: To test the physiological effect of GABA on retinal Horizontal Cells (HCs) of the mammalian retina. It has been shown that HCs express ionotropic GABA receptors, primarily permeable to chloride. The expresion of Na-K-Cl co-transporter (NKCC) at the dendrites of HCs suggests that there is a high concentration of chloride in mammalian HCs leading to their depolarization in response to GABA (Vardi et al. J.Neurosci., 2000, 20:7657). The intracellular chloride concentration in HCs was estimated by means of chloride equilibrium potential in those cells. Methods: GABA-induced currents were studied by means of whole cell recordings on HCs enzymatically dissociated from the rabbit retina. Gramicidin perforated patch was used for the present experiments. The equilibrium potential for chloride was measured in HCs in response to puff application of GABA. Kainate induced currents was tested simultaneously as control. Results: In response to a puff application of 30 uM GABA a reversal potential of -32±8 mV was measured in dissociated HCs under gramicidin perforated patch configuration. After getting the whole cell configuration, reversal potential close to 0 mV was obtained when high chloride (125 mM) was included in the patch pipette. Under current clamp condition, puff application of GABA induces a depolarization in HCs. According to Nerst equation an HC intracellular chloride concentration of ca. 40 mM was estimated. Conclusions: Previous immunocytochemical studies localizes the NKCC that normally intrudes chloride in the dendrites of HCs. Our results strongly supports the idea that GABA induces in situ a depolarization in HCs in the mammalian retina.
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