Presynaptic action of central depressant drugs: inhibition of depolarization-secretion coupling

Chlorpromazine, like raised osmotic pressure, not only increases spontaneous miniature endplate potential frequency (F) in mouse diaphragm (in vitro) but also depresses the slope of log F versus focal presynaptic depolarization. It also depresses the slope of log F versus [Ca], in raised K+ (constant depolarization). Similar effects are seen with pentobarbital, chloral hydrate, chloroform, and lowered pH. The drugs have similar actions in locust muscle, where the transmitter is not acetylcholine.

Water uptake and energy metabolism in brain slices from the rat

1. Exchange of (3)H(2)O with H(2)O takes place rapidly in incubated rat brain slices but at a lower rate in slices from infant brain than from adult brain. The temperature coefficient (Q(10)) of the exchange process, between 37 and 4 degrees C, is 1.76 with infant brain and 1.26 with adult brain. The exchange process is unaffected by the presence of ouabain or 2,4-dinitrophenol. 2. An approximately linear relationship exists between water uptake and the concentration of ATP in the incubated slices in the presence of various concentrations of glucose. Little or no change occurs in water uptake and ATP concentration in the presence of a glucose concentration exceeding 3mm. A linear relationship also exists between the water uptake and ATP concentration in the presence of 10mm-glucose and various concentrations of sodium l-glutamate but the line is parallel to that found with changed glucose concentrations and shifted in the direction of increased water uptake. A similar parallel relationship exists between water uptake and ATP concentration in the presence of 2,4-dinitrophenol, but the amount of water uptake is significantly smaller in the presence of 2,4-dinitrophenol than in its absence. 3. Copper chloride (0.3mm) or mercuric chloride (0.3mm) both increase water uptake and diminish the ATP concentration in slices. Sodium malonate (2mm) or sodium d-glutamate (10mm) has similar effects. 4. Substances, or conditions, affecting water uptake in incubated brain slices may be divided roughly into two classes in accordance with their effects on adenosine triphosphatase and membrane permeability, but there may be considerable lack of specificity.

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.