Effect of glutamate on extracellular potassium activity in isolated retina of cyprinid fish |
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Authors: | MBA Djamgoz |
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Institution: | Department of Pure and Applied Biology, Neurobiology Group, Imperial College, London SW7 2BB, England |
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Abstract: | The effect of (l-)glutamate on extracellular K+ activity of the isolated retina of the cyprinid fish, roach, was investigated using double-barrelled K+-sensitive micro-electrodes. Application of μM-mM glutamate to the retina as a “puff” from an atomizer induced a transient rise in extracellular K+ activity, which was maximal 50–100 μm below the photoreceptor surface. The effect was concentration-dependent, but not related to the state of light adaptation of the retina. In the presence of dinitrophenol or ouabain, the glutamate-induced increase in extracellular K+ activity was maintained.The following conclusions are made. (1) The most likely cellular origin(s) of the glutamate-induced rise in extracellular K+ activity are the photoreceptors and/or the Muller (glial) cells. (2) The mechanism responsible for returning the extracellular K+ activity to normal depends strongly on metabolic, Na+, K+ pump activity. (3) The effect parallels the action of endogenous glutamate, and may be important for modulation of neurotransmission in the intact retina. |
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