Oxygen uptake occurs faster than sodium pumping in bee retina after a light flash

Abstract

When neurones are active there is an entry of Na⁺, which must subsequently be pumped out, and an increase in their oxygen consumption rate ($Q_{{\text{O}}_{\text{2}}}$). The Na⁺ pump derives its energy from ATP, splitting it into ADP and P_i, and it has reasonably been proposed that the changes in concentrations of ATP, ADP and P_i lead to a stimulation of the O₂ consumption by the mitochondria and hence to a restoration of the stock of ATP^1–3. Here we present evidence suggesting that $Q_{{\text{O}}_{\text{2}}}$ must be controlled differently in the retinal photoreceptor cells of the honeybee drone. Stimulation of drone photoreceptors with a flash of light causes an entry of Na⁺ (ref. 4) and a transient increase in $Q{\text{o}}_2$ that indicates respiration of the right order of magnitude to provide ATP to pump the Na⁺ out⁵. We report intracellular recordings of changes in intracellular sodium (Na_i⁺) and potassium (K_i⁺) in response to single light flashes and have compared the time course of extra oxygen consumption (Δ$Q_{{\text{O}}_{\text{2}}}$) with these ion changes and other indices of Na+ pumping. We found that the time course of pumping seems to lag behind the time course of Δ$Q_{{\text{O}}_{\text{2}}}$. It follows that the mitochondrial respiration must be stimulated by some signal which is generated earlier than the rise in ADP produced by the Na⁺ pump.