Temperature dependence of the light response in rat rods.

Abstract

SUMMARY1. The effects of temperature on the light responses of rat rods have been investigated over the range 17-40 'C.2. The amplitude of the light-sensitive current increased with temperature with a mean temperature coefficient (Qlo) of 2 47.3. The amplitude of the Na'-Ca2+, K+ exchange current decreased with temperature when expressed as a fraction of the light-sensitive current, showing that the light-sensitive channel becomes less permeable to calcium as the temperature is raised. The time constant of relaxation of the exchange current was little affected by temperature.4. The flash intensity required to give a half-saturating response increased with temperature with a mean Q1o of 168.5. The responses to single photoisomerizations were determined from amplitude histograms of the responses to dim-flash trains. The amplitude of the response to a single photoisomerization decreased with temperature when expressed as a fraction of the light-sensitive current, but the change was not sufficient to account for the overall decrease in sensitivity.6. The fraction of dim flashes that produced a photoisomerization decreased with temperature. This decrease in photon capture efficiency together with the decrease in the relative size of the single photon event fully accounts for the observed change in sensitivity.7. The speed of the falling phase of the dim-flash response was accelerated more by warming than the rising phase, and it was therefore not possible to superimpose light responses at different temperatures by a simple change in time scale.

The photovoltage of rods and cones in the dark‐adapted mouse retina

“…Rod collecting area was markedly reduced at body temperature compared to room temperature, confirming experiments on rat rods by Robinson et al (1993). Since our data was obtained in separate cells and preparations, we cannot rule out a systematic difference in experimental conditions, other than temperature, affecting our estimates of collecting area.…”

Properties and functional roles of hyperpolarization‐gated currents in guinea‐pig retinal rods

“…Kpump, the rate constant of the pumping process at 22°C, is expected to be 0·413 s¢, a value adequate to match the dark current at this temperature (7 pA with about 80% of the current carried by sodium and the remaining 20% by calcium) (Robinson et al 1993;Demontis et al 1997). The internal sodium concentration attained at thermodynamic equilibrium ([Na¤eq]é), when the free energy of ATP hydrolysis (ÄGATP) balances the free energy of ion transport against the gradient (ÄGNa + ÄGK), will change with the voltage, as described by: In the presence of sodium influx, the sodium pump will generate an electrogenic current if [Na¤]é > [Na¤eq]é.…”

A physiological role for the supramolecular organization of rhodopsin and transducin in rod photoreceptors

“…However, a careful analysis of electrophysiological data on single photon responses (SPRs) that have been largely neglected may reveal unexpected incompatibilities with the classical view, as pointed out recently [45]. A study performed by Robinson et al [50] revealed that the efficiency of photon capture and conversion to an electrical signal by rat rods increases with decreasing temperature. This phenomenon can be quantified by the concept of effective collecting area A c (μm 2 ) which connects the intensity of the light stimulus i (photons/μm 2 ) to the number of effective photoisomerizations Φ i , according to the relation: Φ i = A c i · A c depends on a number of factors, including the geometrical cross section of the rod outer segment accounting for the space distribution of the pigment, the photon absorption characteristics of the ROS and the efficiency of Rh isomerization.…”