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

Within the renal cortical collecting duct (CCD), transepithelial Na(+) absorption and K(+) secretion are linked to basolateral Na(+)-K(+)-ATPase activity. Our purpose was to examine the developmental changes in basolateral Na(+)-K(+)-ATPase-mediated (86)rubidium (Rb) uptake, its inhibitor sensitivity and relationship to pump hydrolytic activity and Na(+) transport. Multiple CCDs ( approximately 6 mm) from maturing rabbits were affixed to coverslips, preincubated at 37 degrees C for 10 min (+/-1-2.5 mM ouabain or 10 or 100 micro M Schering-28080, an inhibitor of H(+)-K(+)-ATPase), and then transferred to prewarmed incubation solution containing tracer amounts of (86)Rb (+/-inhibitors). After 1 min at 37 degrees C, tubular samples were rinsed and permeabilized and isotope counts were measured to calculate basolateral Rb uptake. Ouabain-inhibitable Rb uptake, an index of basolateral Na(+)-K(+) pump activity, increased approximately 3-fold during the 1st 8 wk of postnatal life (P < 0.03). The approximately 2-fold 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 significance. 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 wk). 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 phosphate release from [gamma-(32)P]ATP under maximum velocity (V(max)) conditions, also 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 approximately 2.5-fold increases in Na(+)-K(+)-ATPase activity and ouabain-sensitive Rb uptake between 2- and 6-wk postnatal age suggest that the developmental increase in basolateral transport capacity is due predominantly to an increase in enzyme abundance. The signals mediating the developmental increase in Na(+)-K(+)-ATPase activity in the CCD remain to be defined.

Predicting first-year relapses in children with nephrotic syndrome.

OBJECTIVE: More than half of the children diagnosed with nephrotic syndrome will have relapses. These can be infrequent relapses (IRs: <2 in 6 months or <3 in a year) or frequent relapses (FRs: >2 in 6 months or >3 in a year). Patients who relapse while on alternate day steroids or within 1 month of discontinuation of steroid therapy are considered steroid-dependent (SD; J Pediatr. 1982; 101:514-518). Patients with an IR course have a better long-term prognosis, and many of them have minimal-change disease without mesangial hypercellularity or sclerosis. The purpose of our study was to identify factors at initial presentation that could predict the relapse pattern in the first year after diagnosis, without taking into consideration the histopathology found on renal biopsy. DESIGN: We analyzed the medical records of children who were seen by us before March 1997 and followed for at least 1 year. Variables selected in the study were age, sex, race, presence or absence of hematuria, and days to remission (defined as protein-free) at the initial presentation, because they could relate to the pattern of relapses (ie, IR, FR, and SD). RESULTS: Of 70 patients, 14 were excluded because of insufficient data. There were 38 males (67.9%) and 18 females (32.1%), giving a male:female ratio of 1.8:1. Median age at presentation was 3.25 years (range: 1.5-13), and 76.9% were white, 8.9% black, 7.1% Hispanic, and 7.1% other. Of all the patients, 23 were IR (41.1%), 9 were FR (16.1%), and 24 were SD (42. 9%). Median days to remission were 10 (range: 2-60), on Prednisone 60 mg/M(2) daily. Hematuria was present initially in 26 patients (46. 4%), and absent in 30 (53.6%). Age, sex, race, and hematuria, as independent variables, were not predictors of relapses in the first year. However, using a stratified analysis based on the presence or absence of hematuria, we found that if the remission occurred within the first week of therapy, the patients without hematuria were more likely to be IR. The sensitivity and specificity of this finding were 67% and 89%, respectively, with a positive predictive value of 94%. CONCLUSION: We conclude that of all the presenting features, the rapidity of initial response to steroid therapy combined with the presence of hematuria, could predict future relapses and should be well documented.

Development of a life-threatening anaphylactoid reaction following administration of ioversol in a child.

We report for the first time the case of a 3-year-old girl who developed a severe anaphylactoid reaction following the administration of the nonionic, low osmolar intravenous radiographic contrast agent ioversol. Severe reactions to ioversol have rarely been reported in adult patients and to our knowledge never in children. Health care providers managing children who may require radiologic imaging studies with ioversol should be aware of the potential complications of this radiographic contrast agent.

Nephrotic syndrome associated with hypocomplementemia in a 4-year-old boy with hemophilia B.

PURPOSE: The case of a 4-year-old boy with hemophilia B with inhibitor who developed nephrotic syndrome is described. The possible association between factor IX therapy and nephrotic syndrome in patients with hemophilia B is discussed. PATIENT AND METHODS: A chart review of a 4-year-old boy with hemophilia B and an inhibitor who developed nephrotic syndrome with transient hypocomplementemia was performed. In addition, a literature search was undertaken to determine the prevalence of this association and possible etiologic factors. RESULTS: Although the nephrotic syndrome was resistant to steroid therapy and Bebulin (Osterreichisches Institut für Haemoderivate Ges.M.B.H., Subsidiary of Immuno AG, Vienna, Austria) infusions were continued, the edema resolved and proteinuria decreased. Seven month later, proteinuria, accompanied by transient hypocomplementemia, increased again. A rise in factor IX inhibitor level was observed. The patient received no immunosuppressive therapy, and exhibited a continuous decrease in urinary protein excretion over the following months. DISCUSSION: A discussion about possible differential diagnoses and a review of the literature are presented.

Age dependence of tolerance to anoxia and changes in cytosolic calcium in rabbit renal proximal tubules.

Calcium(Ca2+)-dependent processes mediate, in part, anoxic cell injury. These may account for the difference in sensitivity to anoxia between certain immature and mature renal cells. To address this question, we studied the effects of anoxia on cytosolic free Ca2+ concentration ([Ca2+]i), cell integrity, and transport functions in microdissected proximal convoluted tubules (PCT) of < 3-week-old (newborn) and > 12-week-old (adult) rabbits. Tubules were loaded with 10 microM fura-2 AM by incubation for 60 min at 37 degrees C, and then superfused with isosmotic saline solution gassed with either 95%O2-5%CO2 (control group) or 95%N2-5%CO2 (anoxia group) for 30 min. [Ca2+]i was measured ratiometrically; cell damage was assessed by nuclear binding of propidium iodide (PI). Anoxia resulted in a fourfold increase in [Ca2+]i in adult tubules (from resting values of 245 +/- 10 to 975 +/- 100 nM, P < 0.001), whereas in newborn tubules the rise was significantly less (from resting values of 137 +/- 5 to 165 +/- 5 nM, P < 0.001 between anoxic groups). Transient exposure to 100 mM potassium chloride, which depolarizes the PCT cells, induced increases in [Ca2+]i from baseline, to 920 +/- 90 nM in tubules from adult and to 396 +/- 16 nM in those from newborn rabbits (P < 0.001 between age groups). After exposure to ligands such as parathyroid hormone (PTH) and ATP, [Ca2+]i increased in both newborn and adult tubules, but to lower levels in newborn tubules. The response to PTH and ATP was transient in both age groups, [Ca2+]i returning to baseline levels after 2 min. Following anoxia, tubules from adult animals exhibited staining of all cell nuclei by 1 min exposure to PI, indicative of gross permeabilization of the cells. Nuclei of anoxic immatures tubules did not stain with PI. The sodium-dependent uptakes of a glucose analogue (14C-alpha-methyl-glucopyranoside) and phosphate (32Pi) were preserved in agarose-filled tubules of newborns after anoxia, whereas in those of adults recovery from anoxia was associated with drastic reduction in the uptake of these solutes. Overall, our results suggest that: (1) during anoxia, cell Ca2+ rises to critical levels in PCTs of adults compared with those of < 3-week-old animals, (2) Ca2+ influx occurs via a pathway activated by exposure to high [K+]o, presumably voltage-sensitive Ca2+ channels or reversal of Na(+)-Ca2+ exchange, (3) these pathways are either less active or less abundant in proximal tubules of newborn compared with adult rabbits, and (4) secondary active transport activity and cellular integrity are well preserved after anoxia in PCT cells of newborn but not of adult rabbits.