Kinetics of oxygen consumption and light-induced changes of nucleotides in solitary rod photoreceptors

We made simultaneous measurements of light-induced changes in the rate of oxygen consumption (QO(2)) and transmembrane current of single salamander rod photoreceptors. Since the change of PO2 was suppressed by 2 mM Amytal, an inhibitor of mitochondrial respiration, we conclude that it is mitochondrial in origin. To identify the cause of the change of QO(2), we measured, in batches of rods, the concentrations of ATP and phosphocreatine (PCr). After 3 min of illumination, when the QO(2) had decreased similar to 25%, ATP levels did not change significantly; in contrast, the amount of PCr had decreased similar to 40%. We conclude that either the light-induced decrease of QO(2) is not caused by an increase in [ATP] or [PCr], or that the light-induced change of [PCr] is highly heterogenous in the rod cell.