Isolation of a plasma membrane fraction highly enriched in ouabain-sensitive Na+-K+-ATPase from rat brain white matter

Effect of chlorpromazine on the localization of cAMP phosphodiesterase

Chlorpromazine (CPZ) at dosages of 10 mg/kg body weight (b.wt.) affected the cytochemical localization of cAMP-dependent phosphodiesterase (cAMP PDE) activity in the synapses of the rat frontal cortex. Postsynaptic cAMP PDE activity was inhibited, and presynaptic activity increased. CPZ also inhibited membrane-bound ATPase activity in the frontal cortex. The activity of Na+-K+-ATPase was significantly (P less than 0.005) inhibited in isolated plasma membranes from the rat frontal cortex. CPZ exposure also affected the cytochemical localization of cations with potassium pyroantimonate. Precipitate, which could be removed with 5 mm EGTA, was decreased in the mitochondria and synaptic vesicles in presynaptic areas after CPZ treatment. The incorporation of 45Ca2+ into slices of the rat frontal cortex was also significantly (P less than 0.001) inhibited by CPZ. This ultrastructural study shows that CPZ may affect biochemical events in an opposite manner in the pre- and post-synaptic areas of some neurons of the frontal cortex.

The interaction between calcium and the activation of Na+, K+-ATPase by noradrenaline

The interaction of noradrenaline, various cation chelators and calcium on Na+, K+-ATPase from rat cerebral cortex plasma membranes was studied. It was shown that chelation of inhibitory cations by EGTA, EDTA and dipyridyl activated Na+, K+-ATPase to the same extent as noradrenaline but at higher concentrations; increasing concentrations of EGTA depressed the activation by noradrenaline; calcium in the form of a calcium-EGTA buffer depressed Na+, K+-ATPase at physiological concentrations; the inhibition of Na+, K+-ATPase by calcium is dependent on the magnesium concentration in the assay and the inhibition by calcium was partially reversed by noradrenaline.

Two different Na,K-ATPases in the optic nerve: cells of origin and axonal transport

Two molecular forms of Na,K-ATPase can be isolated from the central nervous system. The two forms can be distinguished by their sensitivities to cardiac glycosides and by the electrophoretic mobilities of their catalytic subunits, alpha and alpha(+). Because Na,K-ATPase is a membrane-bound enzyme, it would be predicted to move in the rapid phase of axonal transport, and this was used as a means to determine which form(s) is made by a defined neuron of the central nervous system. Retinal ganglion cells were labeled in vivo by intravitreal injection of [35S]methionine; the Na,K-ATPase that was axonally transported down the optic nerve was purified, and the alpha and alpha(+) forms were separated by electrophoresis and detected by fluorography. The two forms were synthesized in the retina in approximately equal amounts. The alpha(+) form was the predominant form transported from the retinal ganglion cells to the lateral geniculate nucleus and superior colliculus. The oligodendrocytes and other sheath cells of the excised optic nerve, in contrast, synthesized only the alpha form when incubated in vitro with [35S]methionine. The labeled Na,K-ATPase found at the nerve endings always included a small amount of the alpha form in addition to the alpha(+) form. The proportions of the two forms did not change with time after transport, and the presence of labeled alpha was not affected by infusion of cycloheximide to inhibit intracranial protein synthesis. Hence, although alpha(+) is the predominant form, the evidence suggests that small amounts of the alpha form are also made and transported by retinal ganglion cells.

Immunoreactivity of subunits of the (Na+ + K+)-ATPase. Cross-reactivity of the alpha, alpha + and beta forms in different organs and species

The immunologic cross-reactivity of the alpha and alpha + forms of the large subunit and the beta subunit of the (Na+ + K+)-ATPase from brain and kidney preparations was examined using rabbit antiserum prepared against the purified holo lamb kidney enzyme. As previously reported by Sweadner ((1979) J. Biol. Chem. 254, 6060-6067) phosphorylation of the large subunit of the (Na+ + K+)-ATPase in the presence of Na+, Mg2+, and [gamma-32P]ATP revealed that dog and, very likely, rat brain contain two forms of the large subunit (designated alpha and alpha +) while dog, rat, and lamb kidney contain only one form (alpha). The cross-reactivity of the alpha and alpha + forms in these preparations was investigated by resolving the subunits by SDS-polyacrylamide gel electrophoresis. The separated polypeptides were transferred to unmodified nitrocellulose paper and reacted with rabbit anti-lamb kidney serum, followed by detection of the antigen-antibody complex with 125I-labeled protein A and autoradiography. By this method, the alpha and alpha + forms of rat and dog brain, as well as the alpha form found in kidney, were shown to cross-react. In addition, membranes from human cerebral cortex were shown to contain two immunoreactive bands corresponding to the alpha and alpha + forms of dog brain. In contrast, the brain of the insect Manduca sexta contains only one immunoreactive polypeptide with a molecular weight intermediate to the alpha and alpha + forms of dog brain. The beta subunit from lamb, dog and rat kidney and from dog and rat brain cross-reacts with anti-lamb kidney (Na+ + K+)-ATPase serum. The mobility of the beta subunit from dog and rat brain on SDS-polyacrylamide electrophoresis gels is greater than the mobility of the beta subunit from lamb, rat or dog kidney.