Na+-K+-ATPase-mediated basolateral rubidium uptake in the maturing rabbit cortical collecting duct

Within the renal cortical collecting duct (CCD), transepithelial Na+ absorp tion and K+ secretion are linked to basolateral Na+-K+-ATPase activity. Our purpose was to examine the developmental changes in basolateral Na+-K+-ATP ase-mediated (86)rubidium (Rb) uptake, its inhibitor sensitivity and relati onship to pump hydrolytic activity and Na+ transport. Multiple CCDs (6 mm) from maturing rabbits were affixed to coverslips, preincubated at 37 degree sC for 10 min (+/-1-2.5 mM ouabain or 10 or 100 muM Schering-28080, an inhi bitor of H+-K+-ATPase), and then transferred to prewarmed incubation soluti on containing tracer amounts of Rb-86 (+/- inhibitors). After 1 min at 37 d egreesC, tubular samples were rinsed and permeabilized and isotope counts w ere measured to calculate basolateral Rb uptake. Ouabain-inhibitable Rb upt ake, an index of basolateral Na+-K+ pump activity, increased similar to3-fo ld during the 1st 8 wk of postnatal life (P < 0.03). The <similar to>2- fol d increase in absolute rate of Rb uptake between 1 and 6 wk (2.64 +/- 0.45 to 5.02 +/- 0.32 pmol.min(-1).mm(-1)) did not reach statistical significanc e. The rate of basolateral Rb uptake increased further after the 6th wk of life to 7.29 +/- 0.53 pmol.min(-1).mm(-1) in adult animals (P, 0.03 vs. 6 w k). Schering-28080 failed to inhibit Rb uptake, implying that functional H-K+-ATPase is absent at the basolateral membrane. Na+-K+-ATPase hydrolytic activity, determined by using a microassay that measured inorganic phosphat e release from [gamma-P-32]ATP under maximum velocity (Vmax) conditions, al so increased in the differentiating CCD (from 316.2 +/- 44.4 pmol.h(-1).mm( -1) at 2 wk to 555.9 +/- 105.1 at 4 wk to 789.7 +/- 145.0 at 6 wk; r = 1.0 by linear regression analysis; P < 0.005). The parallel <similar to>2.5-fol d increases in Na+-K+-ATPase activity and ouabain-sensitive Rb uptake betwe en 2- and 6-wk postnatal age suggest that the developmental increase in bas olateral transport capacity is due predominantly to an increase in enzyme a bundance. The signals mediating the developmental increase in Na+-K+-ATPase activity in the CCD remain to be defined.