Photic modulation of a highly sensitive, near-infrared light-scattering signal recorded from intact retinal photoreceptors.
On stimulation by green flashes, the isolated, aspartate-treated bovine retina exhibits transient changes in the scattering of near-infrared (880 nm) light. A single component, termed the "ATR" (a flash-induced scattering signal, where ATR designates amplified transient-retina), dominates the amplitude and rising-phase kinetics of the initial peak of the light-scattering response. Superfusion with physiological solution containing low Na+ concentration reversibly abolishes the photoreceptor electroretinographic response but preserves the ATR signal, indicating a receptoral origin for the ATR. The increase of ATR amplitude (A/Amax) with flash intensity (R*/R, where R indicates rhodopsin) is described by A/Amax = (1- e-kR*/R), with R*/R = k-1 occurring on generation of approximately two photoactivated rhodopsins (R*s) per disc surface in the rod outer segment. Weak background light and bright flashes reversibly depress the ATR. Kinetic and sensitivity data suggest a basis of the ATR in stochastic, unit activation events, each initiated by a single R*. They further suggest an essential invariance of the unit event under differing conditions of illumination. A delay, apparently governed by the lifetime of a light-activated substance regulating ATR generation, precedes ATR recovery after a bright flash. The flash dependence of the delay period indicates an upper limit of 3 s for the lifetime of R* in the ATR-generating process. The unit event appears to be an R*-catalyzed and disc-localized reaction of phototransduction.
Pepperberg
D R
DR
Institut für Biophysik und Strahlenbiologie, Albert-Ludwigs Universität, Freiburg, Federal Republic of Germany.
Kahlert
M
M
Krause
A
A
Hofmann
K P
KP
D000818:Animals; D002417:Cattle; D004594:Electrophysiology; D004596:Electroretinography; D007259:Infrared Rays; D007700:Kinetics; D008027:Light; D008433:Mathematics; D010786:Photoreceptor Cells / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology; D012542:Scattering, Radiation
D012243:Rhodopsin