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B. Li, W. Shen; Preferential Distribution of Cation Cl- Cotransporters in the Dendrites of Goldfish Bipolar Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4589.
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The GABA feedforward from HCs contributes to the center-surround response on bipolar cells. The effect of GABA could be either inhibitory or excitatory depending on the [Cl-]i in the BC’s dendrites. NKCC1 and KCC2 play a crucial role in the control of the [Cl-]i by uptaking or extruding Cl-, respectively. Discerning the distribution of NKCC1 and KCC2 in the local regions will serve to better understand the function of GABA in the distal retina.
Western blotting technique was performed to verify the specific binding for NKCC1 and KCC2 antibodies in adult goldfish retinas. Confocal imaging and Immunocytochemical studies were conducted on goldfish retinal vertical sections to localize NKCC1 and KCC2.
A single Western blotting band at MW 150kDa or 140kDa was respectively probed by NKCC1 or KCC2 antibodies in goldfish retinas which matched the predicted MW for the proteins in mouse spines. The single antibody labeling results showed that NKCC1 was only present in the distal retinas and KCC2 was strongly present in both OPL and IPL. The inner nuclear layer and ganglion cell layer were lightly labeled by KCC2. Double-labeling results showed that NKCC1 was present in the PKC-positive On-BC dendrites, horizontal cells and possibly photoreceptor terminals, whereas KCC2 was present in the dendrites of the Off-BCs labeled by antibody for GluR4, an AMPA receptor subunit. In addition, KCC2 strongly labeled PKC-positive axon terminals of On-BCs where NKCC1 was absent.
The [Cl-] might be higher in the dendrites of On-BCs than in the Off-BCs in goldfish BCs. Thus GABA may depolarize the On-BCs and hyperpolarize Off-BCs in the distal retinas, counteracting glutamate responses in BCs. Also, a [Cl-] gradient might be present in PKC-positive On-BCs, which leads to an excitatory Cl- response in the dendrites and an inhibitory Cl- response in the axon terminals.
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