EFFECTS OF PHOTORECEPTOR METABOLISM ON INTERSTITIAL AND GLIAL-CELL PHIN BEE RETINA - EVIDENCE OF A ROLE FOR NH4+

1. Measurements were made with pH microelectrodes in superfused slices of the retina of the honey-bee drone. In the dark, the mean +/- S.E.M . pH values in the three compartments of the tissue were: neurones (ph otoreceptors), 6 . 99+/-0 . 04; glial cells (outer pigment cells), 7 . 31+/-0 . 03; extracellular space, 6 . 60+/-0 . 03. 2. Stimulation of the photoreceptors with light caused transient pH changes: a decrease in the photoreceptors (pH(n)) and in the glial cells (pH(g)), and an i ncrease in the interstitial clefts (pH(o)). 3. The effects of inhibiti on and activation of aerobic metabolism showed that part, perhaps all, of the light-induced Delta pH(o) resulted from the increased aerobic metabolism in the photoreceptors; 4. Addition of 2 nM NH4+ to the supe rfusate produced changes in pH(o) and pH(g) of the same sign as and si milar amplitude to those caused by light stimulation. Manipulation of transmembrane pH gradients had similar effects on changes in pH(o) ind uced by light or by exogenous NH4+. 5. Measurements with NH4+-sensitiv e microelectrodes showed that stimulation of aerobic metabolism in the photoreceptors increased [NH4+](o) and also that exogenous NK4+/NH3 w as taken up by cells, presumably the glial cells. 6. We conclude that within seconds of an increase in the aerobic metabolism in the photore ceptors, they release an increased amount of NH4+/NH3 which affects pH (o) and enters glial cells. Other evidence suggests that in drone reti na the glial cells supply the neurones with amino acids as substrates of energy metabolism; the present results suggest that fixed nitrogen is returned to the glial cells as NH4+/NH3.