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E.P. Hornstein, J. Verweij, J.L. Schnapf; Electrical coupling between red and green cones in primate retina . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1145.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Color vision depends on differences in the action spectra of cone photoreceptors. The presence of gap junctions at cone terminals in primate retina suggests that cones interact electrically. Electrical coupling between cones of different spectral types may influence cone spectral sensitivity. We investigated the electrical properties of cone–cone coupling in monkey retina and measured the effects of coupling on red and green cone spectral sensitivity. Methods: Patch–clamp recordings were made from cones in isolated macaque monkey retina. Results: Pairs of neighboring cones were simultaneously voltage–clamped. The average coupling conductance between cones was about 650 pS and did not vary significantly for green–green pairs, red–red pairs or red–green pairs. Signal transfer between cones was blocked by the gap junction blocker carbenoxolone, but not by the glutamate receptor antagonists CNQX and APB, consistent with electrical communication through gap junctions. Photovoltage responses in single red and green cones to flashes of 500 nm and 660 nm light revealed that neighboring coupled cones of different spectral type influenced the recorded cone's spectral sensitivity. Recordings from green cones showed that sensitivity to long wavelengths was increased compared to spectral sensitivities measured directly from green cone outer segments, consistent with input from red cones. Using a long wavelength light to preferentially bleach red cone photopigment, we found that the increased long wavelength sensitivity disappeared and that measured spectral sensitivities matched those of a pure green cone. Recordings from red cones showed no apparent coupling from green cones before bleach, but bleaching with a long wavelength light resulted in a relative increase in sensitivity to shorter wavelengths, consistent with coupling from green and/or blue cones. Conclusions: Cone photoreceptors in primate retina are electrically coupled. There is no significant difference between coupling conductances for homologous or heterologous pairs of cones. Our results demonstrate that electrical coupling between red and green cones results in a mixture of spectrally pure cone signals.
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