Distribution of (Na⁺, K⁺)ATPase on Canine Hepatocyte Plasma Membranes

-Analysis by Quantitative Ferritin Immunoelectron Microscopy-

Abstract

(Na⁺, K⁺) ATPase (holo-enzyme) and its a and β subunits were purified from canine kidney by using lectin-Sepharose affinity chromatography, and the antibodies against them were raised in rabbits. The antibody against the holoenzyme inhibited not only kidney but also liver (Na⁺, K⁺)A TPase activities almost completely. Distribution of (Na⁺, K⁺)A TPase on the cell sur faces of prefixed and isolated canine hepatocytes was investigated by quantitative ferritin immu noelectron microscopy using these antibodies, and the following results were obtained.
1) (Na⁺, K⁺) ATPase exists on the bile canalicular as well as on th e sinusoidal and lateral surfaces of hepatocytes.
2) The av erage particle density on the bile canalicular surface was -2.5 times higher than on the sinusoid-lateral surface.
3) The total number of t h e enzyme on the sinusoid-lateral surface was, however -3 times higher than that on the bile canalicular surface, because the canalicular surface represents only 13%, while the sinusoid-lateral surface 87% of the total hepatocyte surface.
4) We suggested that (Na⁺, K⁺) ATPase on the bile canalicular pl a sma membrane is responsible for the bile acid-independent bile flow, while that on the sinusoid-lateral surface for the various active transport processes.