BOENA OEGovIó, DAVORKA Domrovló-JENIK and S. MILK0vIÓWith 4 Figures Summary. The treatment of rat kidney plasma membranes with sodium dodecyl sulphate (SDS) did not essentially affect the ability of the membranes for 3H-aldosterone binding as compared with the intact plasma membranes (Oegovió et al., 1977). A gel filtration of 311.aldosterone -kidney plasma membranes complex on Sepharose GB yielded 2 protein and 2 311-aldosterone peaks. The proteins which were eluted in the first peak were associated with the first 311.aldosterone peak while the second 3H-aldosterone peak was eluted with Ve corresponding to Ve of free 311-aldosterone.Spironolactone, a competitive antagonist of aldosterone, prevented the binding of 3H.aldosterone to the membrane proteins.The results demonstrated a high affinity of the kidney plasma membranes solubilized with SDS and a specificity of aldosterone binding to the plasma membrane proteins of higher molecular mass.
The postnatal development of the sodium transport mechanism in the rat kidney, as judged by the activity of renal plasma membrane Na-K-ATPase, was studied. Highly purified kidney plasma membranes as verified by electron microscopic and enzyme examinations, were used. Na-K-ATPase activity (μmol Pi/mg protein/h) increases exponentially from 16.9 ± 1.94 found at birth to the mature level of 43.1 ± 2.16 reached at the age of 41 days. This finding paralleled our results of SDS-polyacrylamide gel disc electrophoresis, showing a completely differentiated plasma membrane protein structure at birth, the maturation of which proceeds only as quantitative enrichment of some protein fractions in the further postnatal period.
Fluid absorption from the alveolar space in vivo is dependent on glucose in the alveolar fluid. To evaluate underlying mechanisms, glucose transport and Na+/K+-ATPase activity were measured in a pure preparation of alveolar type II (AII) cells in primary monolayer cultures (day 4). The apical plasma membrane transport of α-methyl-D-glucoside, a nonmetabolizable hexose, was characterized by its sodium concentration dependence, by differential sensitivities to phlorezin and to phloretin, and by its substrate dependence. Na+/ K+-ATPase activity of cultured AII cells was quantified by enzymatic coupling of ATP hydrolysis to fluorescent NAD appearance. The data characterize pulmonary AII cells by their apical sodium-glucose symport activity and by their basolateral sodium-potassium transport enzyme activity.
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