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P De la Villa, C Varela; Intracellular Chloride Concentration in Rod Bipolar Cells Allow Opposite Responses to GABA in the Dendrites and the Axon Terminal . Invest. Ophthalmol. Vis. Sci. 2002;43(13):894.
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Purpose: To study the intracellular chloride concentration in rod bipolar cells (RBCs) of the mouse retina. GABA gates anion channels primarily permeable to chloride in RBCs; opposite effects of GABA on different cellular regions have been suggested, probably determined by the differential targeting of two chloride transporters (Vardi et al. J.Neurosci., 2000, 20:7657); no evidence for different responses to GABA between cellular regions have been shown to date. Methods: GABA-induced currents were studied by means of whole cell recordings on RBCs enzymatically dissociated from the mouse retina. Gramicidin perforated patch was used for the present experiments. The equilibrium potential for chloride was measured in different compartments of the RBCs in response to puff application of GABA, for this purpose, experiments were carried out on full shaped RBCs and cells without axon terminal. Results: In response to a puff application of 30 µM GABA a reversal potential of –63 8 mV was measured in dissociated RBCs that maintain their full shape; this GABA response is originated mainly in the axon terminal. According to Nerst equation an intracellular chloride concentration of 13 mM was calculated. Chloride equilibrium potential was also measured in bipolar cells that lacked the axon terminal and a value of -37 6 mV was obtained. Intracellular chloride for cells without axon terminal was estimated to be 35 mM, thus corresponding to the dendrites and soma. Conclusion: Previous immunocytochemical studies localizes the K-Cl cotransporter, that normally extrudes chloride, in the axon terminal and the Na-K-Cl cotransporter, that normally accumulates chloride, at the dendrites of RBCs. Our results strongly supports the idea that GABA induce opposite effects on dendrites and axon terminal of the same rod bipolar cell.
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