title: Proximal tubular reabsorption and Na-K-ATPase activity in remnant kidney of young rats.
abstract: In rats unilaterally nephrectomized (NX) in infancy, the compensatory growth of the remnant kidney is due first to hypertrophy and hyperplasia, but after 2 wk only to hyperplasia. We studied proximal tubular adaptation (reabsorption, Na-K-ATPase activity, length, and basolateral membrane area) 2 and 8 wk after NX. The rats were NX at 5 days of age. The size of remnant kidney obtained from uninephrectomized rats was 125% at 2 wk and 179% at 8 wk relative to the appropriate time-related controls. Single-nephron glomerular filtration rate in the uninephrectomized group was doubled relative to controls, whereas fractional reabsorption by the proximal tubule was unchanged. Na-K-ATPase activity per millimeter of proximal convoluted tubule (PCT) was significantly increased in the uninephrectomized group relative to controls at 2 but not 8 wk. The area of the basolateral cell membrane per millimeter PCT was unchanged at both 2 and 8 wk, which suggests that the density of enzyme units inserted in the membrane was increased at 2 but not at 8 wk. PCT length was increased at 8 but not at 2 wk. There was a close correlation between total PCT Na-K-ATPase activity and filtered sodium (r = 0.999) and between total PCT Na-K-ATPase activity and PCT sodium reabsorption (r = 0.998). We conclude that the proximal tubule can adapt to an increased filtered load by increasing the density of transporting units or by increasing the tubular length. The latter stage may be attained only in young growing animals.
mesh_terms: D000042:Absorption; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D009392:Nephrectomy; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase