INHIBITION OF SYNAPTOSOMAL NORADRENALINE UPTAKE BY VERATRIDINE, GRAMICIDIN D AND VALINOMYCIN

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Abstract
Abstract— —The effects of brief exposures of rat brain synaptosomes to veratridine, gramicidin D and valinomycin on noradrenaline uptake were investigated. All three drugs inhibited the Na+‐dependent component of noradrenaline uptake by synaptosomes. These effects were independent of extracellular Ca2 + concentrations, indicating that the reductions were not due to the release of newly accumulated noradrenaline.Gramicidin D reduced the Vmax for noradrenaline uptake, whereas veratridine and valinomycin reduced the Vmax and also increased the Vm for uptake.Most of these findings can be explained on the basis of the effects that these drugs have on the inward‐directed electrochemical gradients for Na+ across synaptosomal membranes, although, in the cases of veratridine and valinomycin, the elevated Km's suggest that an impairment of noradrenaline binding to its carriers might also be involved.