METABOLIC SIGNALING BETWEEN PHOTORECEPTORS AND GLIAL-CELLS IN THE RETINA OF THE DRONE (APIS-MELLIFERA)

Experimental evidence showing metabolic interaction and signaling between photoreceptors-neurons and glial cells of the honeybee drone retina is presented. In this tissue [H-3]2-deoxyglucose ([H-3]2DG) in the dark and during repetitive light stimulation is phosphorylated to [H-3]2-deoxyglucose-6P ([H-3]2DG-6P) almost exclusively in the glial cells. Hence, stimulus-induced changes in the rate of formation of [H-3]2DG-6P occurs predominantly in the glial cells. Repetitive stimulation of the photoreceptors with light flashes induced about a 47% rise in the rate of formation of [H-3]2DG-6P in the glial cells and this effect is probably due to the activation of hexokinase. The potent inhibitor of glycolysis iodoacetic acid (IAA), inhibited this phosphorylation by about 75%. Probably this was largely due to an about 70% decrease of adenosine triphosphate (ATP). Exposure of the retina to IAA suppressed the transient rise in oxygen consumption (triangle QO2) in the photoreceptors and subsequently the light-induced receptor potential. This indicates that the supply of a glycolytic substrate by glial cells to the photoreceptors is greatly reduced by IAA. Anoxia, by rapidly suppressing QO2, abolished the receptor potential of the photoreceptors and caused a rapid drop of about 50% in the ATP content of the retina. At the same time the formation of [H-3]2DG-6P was inhibited by about 30%. This indicates that respiring photoreceptors send a metabolic signal to glial cells which is suppressed by anoxia.