ALTERATIONS OF NA-ATPASE ACTIVITY AFTER HYPOXIA AND REOXYGENATION IN THE PERFUSED-RAT-LIVER - AN ELECTRON-MICROSCOPIC CYTOCHEMICAL STUDY(,K+)

Background/Aims: Using the cerium technique for ultrastructural cytoch emical studies, Na+,K+-ATPase activity was investigated in hypoxic and reoxygenated rat liver. Methods: In the control group, the livers mer e perfused with oxygenated hemoglobin-free Krebs-Henseleit buffer for 1 h, For hypoxia (60 min), the flow rate of the perfusate was decrease d and oxygen was replaced by nitrogen, For reoxygenation, the liver wa s reperfused under oxygenated conditions for 5 min after 60 min of hyp oxia. Results: In control livers, a strong Na+,K+-ATPase activity was detected at the basolateral membrane of hepatocytes while the apical m embrane forming the bile canaliculi did not display any staining. In h ypoxic livers, Na+,K+-ATPase activity had ceased in the plasma membran e of hepatocytes. In reoxygenated livers, Na+,K+-ATPase was rapidly re activated in the basolateral hepatic membrane. The membrane of blebs g enerated during the hypoxic phase also showed enzyme activity, In addi tion, a striking accumulation of reaction product could be observed in about 10% of the apical membranes lining the bile canaliculi, Conclus ion: The results indicate a plasticity of the Na+,K+-ATPase in hypoxic and reoxygenated rat liver.