COUPLING OF NA,K-ATPASE WITH SODIUM-CHANNELS IN PLASMA-MEMBRANES OF RAT-BRAIN SYNAPTOSOMES

Effect of neurotoxins veratrine (100-mu-g/ml) and tetrodotoxin (1-mu-M) on the binding of H-3-ouabain 10(-8)M) with Na,K-ATPase of intact synaptosomes and isolated synaptic membranes was studied. The persistent opening of sodium channels in synaptosomes by veratrine results in an increase of specific binding of the labeled ligand by 20%. A similar effect was caused by Na/H exchanger monensin. Destruction of microtubules with vinblastine and colchicin has no influence on veratrine action, while depolymerization of microfilaments with cytocholasin B reverses the neurotoxin effect. In isolated synaptic membranes veratrine and tetrodotoxin stimulate ouabain binding, the absolute veratrine-induced increment being several times higher in the presence of ATP than in its absence. Since the closed vesicles of any type are not permeable to ATP and ouabain, it means that in the isolated membranes an interaction between sodium channels and Na,K-ATPase molecules takes place. In intact nerve endings such a mechanism may be operative along with the known ways of control of sodium pump and its ouabain-binding site.