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V.C. Smith, J. Pokorny, P.D. Gamlin, O.S. Packer, B.B. Peterson, D.M. Dacey; Functional Architecture of the Photoreceptive Ganglion Cell in Primate Retina: Spectral Sensitivity and Dynamics of the Intrinsic Response . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5185.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Human retina contains a novel vitamin A-based photopigment with λmax ~480 nm (Hankins and Lucas, Curr. Biol. 2002). In rat retina phototransduction in melanopsin-containing ganglion cells is also mediated by a photopigment with λmax ~480 nm (Berson, et al., Science 2002). Here we characterize the spectral tuning and response time course of the intrinsic light response of melanopsin-containing ganglion cells in the macaque monkey retina (Dacey et al., ARVO 2003).Methods: Ganglion cells were targeted for intracellular recording after retrograde labeling (Peterson et al., ARVO 2003) in an in vitro preparation of the intact retina. To assess intrinsic photosensitivity, L-AP4 and CNQX were bath-applied to remove excitatory input to inner retina. Response peaks to 10 sec pulses were measured at 10 wavelengths over a 3 log unit range. Michaelis-Menton fits to intensity-response functions gave responsivity (Rmax/Qsat) as a function of wavelength. The spectral responsivity data were well fit by Vitamin A1 pigment nomograms. The time course of the average membrane potential was modeled as sums of exponential-based functions. Results: The peak sensitivity for 4 cells varied from 481 to 487 nm and the group data were best fit by a λmax of 483 nm. The smallest reproducible response was a ~3 mV depolarization with time to peak of ~12 sec. As quantal level increased, the response speeded and developed an initial transient. At highest levels the peak transient response was ~15 mV with time to peak of ~1.5 sec. The membrane potential remained depolarized, with elevated spike rate for many seconds following stimulus offset. The dynamics of this response could be described by the sum of three underlying functions that captured the slow depolarizing response, the initial transient, and the late, sustained depolarization. The early transient and late depolarization may reflect the activation of separate voltage-gated channels recruited at depolarized membrane potentials. Conclusions: A novel photopigment with a λmax of ~483 nm is the basis of phototransduction in macaque melanopsin-containing ganglion cells. The response dynamics probably reflect the sum of the photocurrent and at least two other voltage-gated currents.
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