Tetrodotoxin-sensitive uptake of ions and water byslices of rat brain in vitro.

1. Under certain conditions the processes that bring about increased Na(+) influx and water uptake into rat brain slices have a tetrodotoxin-sensitive component. 2. Incubation of slices in the absence of glucose, or in the presence of ouabain (0.1mm), protoveratrine (10mum) or electrical stimuli, leads to increased uptakes of water and Na(+) that are partially suppressed by tetrodotoxin (3mum). 3. The increased water uptake and Na(+) influx due to the presence of 30mum-2,4-dinitrophenol or of 100mm-potassium chloride are unaffected by tetrodotoxin. 4. The additional presence of 27mm-potassium chloride diminishes, or abolishes, the inhibitory effects of tetrodotoxin on the increased uptakes of water and Na(+) found on incubation in the absence of glucose or in the presence of protoveratrine. 5. Ouabain increases Na(+) influx into caudate nuclei from rat brain and this process is suppressed by tetrodotoxin. Ouabain does not increase water uptake in the caudate nuclei. 6. Diminution of Na(+) influx in slices due to tetrodotoxin is not accompanied by an equal efflux of K(+). 7. It is concluded that glial-cell membranes are permeable to K(+) and Cl(-) and, as a consequence, when K(+) is released from neurons in association with action potentials it, together with water, moves into the glial cells. The major consequence of K(+) (and Cl(-)) permeability of the glial cell is therefore a buffering of the extracellular K(+) concentration. 8. l-Glutamate presents an anomalous feature that may indicate that its effects are not restricted to neurons. 9. Calculations are made of the increase of K(+) flux into the glia in the presence of ouabain or of protoveratrine or in the absence of glucose or on application of electrical impulses.