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 was measured in 300-.mu.m slices of drone retina at 22.degree. C. To measure .DELTA.QO2 (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 2 sites in the slice and .DELTA.QO2 was calculated by a computer using Fourier transforms. After a 40-ms flash of intense light, .DELTA.QO2 reached a peak of 40 .mu.l O2/g .cntdot. min and then declined exponentially to the baseline with a time constant .tau.1 = 4.96 .+-. 0.49 s (SD, n = 10). The rising phase was characterized by a time constant .tau.2 = 1.90 .+-. 0.35 (SD, n = 10). The peak amplitude of .DELTA.QO2 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 .DELTA.QO2. With these changes, however, the kinetics of .DELTA.QO2(t) were unchanged. The recovery phase is probably rate-limited by a single reaction with 1st-order kinetics. This reaction may be the working of the Na pump. Exposure of the retina to high concentrations of ouabain or strophanthidin (inhibitors of the Na pump) reduced the peak amplitude of .DELTA.QO2 by .apprx. 80% and increased .tau.1. The increase of .tau.1 was an exponential function of the time of exposure to the cardioactive steroids. It seems likely that the greatest part of .DELTA.QO2 is used for the working of the pump, whose activity is the mechanism underlying the rate constant of the descending limb of .DELTA.QO2(t).