Endogenous activators and inhibitors of Na, K-ATPase induced by acetylcholine

Preincubation of rat brain homogenates with acetylcholine (ACh) in concentrations of 10(-3)-10(-5) M for 60 minutes produces an essential increment (15-30%) in activity of microsomal Na, K-ATPase. Analogous effect was exerted by the acetylcholinesterase inhibitor eserine (10(-5)-10(-6) M). Acetylcholine has no effect in the presence of actinomycin D. Dialysis of microsomes isolated from the homogenate incubated with ACh leads to a decrease in the enzyme activity and release to the dialysate of low-molecular factor activating Na, K-ATPase of intact microsomes. The latter fact evidences the ACh-induced synthesis of activating factor and inhibition of Na, K-ATPase synthesis. After the animals are administered eserine (0.2-0.4 mg/kg), isolated microsomes show a reduced level of Na, K-ATPase (by 10-15%). Dialysis of microsomes leads to an appreciable elevation (by approximately 40%) of the enzyme activity and release into the dialysate of the inhibitory factor. The differences in the effects of eserine in vivo and in vitro suggest that during the impairment of brain integrity certain effects are excluded from the processes of the control over Na, K-ATPase activity. One of these may involve the impairment of intercellular interactions, for example, the disappearance of the effect on cholinoceptive cells of internuncial neurons that release inhibitory neurotransmitters (catecholamines).