Effects of mammalian brain extracts and chlormadinone acetate on neuronal Na+,K+-ATPase and electrogenic Na+,K+-pump activity in vitro.
Acid-acetone extracts of brain (from beef and guinea pig) and chlormadinone acetate (CMA) were compared with ouabain for their ability to inhibit the electrogenic Na+,K+-pump and the Na+,K+-ATPase of neuronal tissues. The membrane potential of neurones in the paravertebral sympathetic ganglion of the bullfrog was recorded in K+-free Ringer's solution by means of the sucrose gap technique. The potassium activated hyperpolarization (K+H), induced by the re-introduction of potassium, was used as an index of electrogenic Na+, K+-pumping. The K+H was blocked by 1 microM ouabain. Na+,K+-ATPase activity was measured in microsomal membrane preparations of frog and beef brain using a continuous spectrophotometric assay. Although ouabain consistently inhibited beef brain Na+,K+-ATPase (IC50 = 2.2 microM), acid-acetone extracts prepared from guinea pig and beef brain produced only partial inhibition. Neither of the extracts significantly reduced the K+H of the frog ganglion. CMA inhibited Na+,K+-ATPase prepared from bullfrog brain and spinal cord with slightly greater potency (IC50 = 4.5 microM) than did ouabain (IC50 = 10 microM). In contrast, electrogenic Na+,K+-pumping (i.e. the K+H) in the frog ganglion was not affected by this steroid. It is concluded that although both the extracts and CMA inhibited Na+,K+-ATPase, neither can be considered ouabain-like due to their failure to affect the electrogenic Na+,K+-pump in situ.
P E
PE
Rafuse
A F
AF
Almeida
S F
SF
Kwan
P A
PA
Smith
D000818:Animals; D001923:Brain Chemistry; D002715:Chlormadinone Acetate / Q000494:pharmacology*; D005728:Ganglia, Sympathetic / Q000187:drug effects* / Q000201:enzymology; D066298:In Vitro Techniques; D010042:Ouabain / Q000494:pharmacology*; D011892:Rana catesbeiana; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D002715:Chlormadinone Acetate; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase