Kinetics of oxygen consumption after a single flash of light in photoreceptors of the drone (Apis mellifera)

Abstract

The time course of the rate of oxygen consumption (Qo2) after a single flash of light has been measured in 300-µm slices of drone retina at 22 °C. To measure ΔQo2(t), the change in Qo2 from its level in darkness, the transients of the partial pressure of O2 (Po2) were recorded with O2 microelectrodes simultaneously in two sites in the slice and ΔQo2 was calculated by a computer using Fourier transforms. After a 40-ms flash of intense light, ΔQo2 reached a peak of 40 µl O2/g · min and then declined exponentially to the baseline with a time constant τ1 = 4.96 ± 0.49 s (SD, n = 10). The rising phase was characterized by a time constant τ2 = 1.90 ± 0.35 s (SD, n = 10). The peak amplitude of ΔQo2 increased linearly with the log of the light intensity. Replacement of Na+ by choline, known to decrease greatly the light-induced transmembrane current, caused a 63% decrease of ΔQo2. With these changes, however, the kinetics of ΔQo2(t) were unchanged. This suggested that the recovery phase is rate-limited by a single reaction with apparent first-order kinetics. Evidence is provided that suggests that this reaction may be the working of the sodium pump. Exposure of the retina to high concentrations of ouabain or strophanthidin (inhibitors of the sodium pump) reduced the peak amplitude of ΔQo2 by ~80% and increased τ1. The increase of τ1 was an exponential function of the time of exposure to the cardioactive steroids. Hence, it seems likely that the greatest part of ΔQo2 is used for the working of the pump, whose activity is the mechanism underlying the rate constant of the descending limb of ΔQo2(t). © 1982, Rockefeller University Press., All rights reserved.