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RA Jacoby, SM Wu; Ampa And Kainate Receptors On Primate Bipolar Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3767.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine whether AMPA, kainate, or both types of glutamate receptors are present on the dendrites of primate bipolar cells. Methods: Bipolar cells were recorded under whole cell voltage clamp conditions using a light-adapted primate (macaque or baboon) retinal slice preparation. Picrotoxin, strychnine, cyclothiazide, GYKI 52466, and SYM 2081 were used to investigate response pharmacology. Cellular morphology was visualized with Lucifer yellow from the recording pipette and confocal microscopy. Results: In some bipolar cells, glutamate applied focally to the outer plexiform layer activated at least three distinct conductances. In normal Ringers solution, there was an initial transient cation current, which was followed by a more sustained chloride current. The slower, sustained chloride current was not present in axotomized cells. The transient cation-mediated response could be reversibly blocked by SYM 2081, a kainate receptor agonist, and was unaffected by GYKI 52466, an AMPA receptor blocker, or cyclothiazide, which potentiates the responses of AMPA receptors but not kainate receptors. This transient current appears to be mediated by kainate receptors. The third current is a smaller, slower-activating cation current that is enhanced by cyclothiazide and is sensitive to GYKI 52466, suggesting activity by AMPA receptors. The bipolar cells exhibiting these responses had small dendrites, apparently contacting only one or two photoreceptors, and relatively compact axon terminals ramifying in the distal half of the inner plexiform layer (IPL). Therefore, they are likely to be OFF midget bipolar cells Conclusions: These results suggest that OFF midget bipolar cells have both kainate and AMPA type glutamate receptors on their dendrites. The responses mediated by the two types of receptors have different kinetics and therefore they may mediate different components of the bipolar cell light response.
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