Abstract
Distribution of Na+K+-ATPase (EC. 3.6.1.3) and its susceptibility to noradrenaline (NA) were studied on electronmicroscopically characterized subcellular fractions of rat brain cortex. The highest specific activity of NaK+-ATPase was present in synaptosomal fraction disrupted in distilled water (29.52 +/- 5.53 mumoles phosphate/mg protein/hour). In the presence of 1 mM EGTA significantly higher specific activity was determined in all fractions studied, except homogenate and synaptosome. The effect of NA was studied in concentration range from 10(-6)--10(-3) M. 10(-4) M of NA produced the highest activation of the enzyme in different fractions. Also in the presence of EGTA NA was able to increase the enzyme activity. The effect of NA was much more marked on disrupted synaptosomal fraction. No qualitative differences have been found between the Na+K+-ATPase activities exhibited by the synaptosomal fraction and by other subcellular fractions with respect to susceptibility to NA. Therefore, it seems very probable that NA might modulate neurochemical transmission not only via an effect on nerve terminals but also via stimulating other part of the neuron.
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