Movement of Potassium into Glial Cells in the Retina of the Drone, Apis mellifera, During Photostimulation
Experiments on the drone retina have led to direct demonstrations of metabolic and ionic interactions between glial cells and sensory neurons. The tissue is composed of two essentially uniform populations of cells: photoreceptors and pigmented glial cells (Perrelet, 1970). The glial cells are not directly sensitive to light, but photostimulation of the photoreceptors causes an increase in glycogen turnover in the glial cells (Evequoz et al.1978). Measurements with intracellular, double-barrelled ion-sensitive electrodes have shown that light stimulation also causes potassium activity (aK) in the photoreceptors to decrease by about 25 %, from a mean value of 79 mmol/l to a mean of 67.5 mmol/l (Coles and Tsacopoulos, 1979). Simultaneously, aK in the glial cells rises from a mean of 52 mmol/l to a mean of 66 mmol/l; since the total volume of the glia is greater than that of the photoreceptors, and the extracellular (e.c.) space fraction is thought to be less than 5 % (Shaw, 1977), the results can most readily be explained by supposing that K+ ions leave the photoreceptors and enter the glia (see Coles and Tsacopoulos, 1979 for details). In the present paper we report that these ion movements are not accompanied by large changes in the volume of the e.c. space.
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