Focal segmental glomerular sclerosis in a patient with neurofibromatosis type I.

A 22 -year-old white man was found to have a serum creatinine level of 3.4 mg/dL (259 micromol/L) and 6 g of protein in a 24-hour urine collection. Laboratory studies performed 5 years prior showed no evidence of abnormal renal function.

Regional localization of renal Na(+)-H+ antiporter: response to respiratory acidosis.

The Na(+)-H+ antiporter of renal brush-border membranes has been well characterized and plays a role in adaptation to acidosis. Na(+)-H+ antiporter activity has been described in other renal regions, but its kinetics as well as its role in adaptation to acidosis are unclear. Thus we measured Na(+)-H+ antiporter activity in membrane vesicles of outer and inner stripes of outer medulla (OSOM and ISOM, respectively) and in plasma membranes from papilla and compared it to Na(+)-H+ antiporter activity of the cortex in control and hypercapnic rabbits.

Stimulation of H+ secretion by CO2 in turtle bladder: role of intracellular pH, exocytosis, and calcium.

We studied the interaction of intracellular pH, exocytosis, and cell calcium on the stimulation of H+ secretion by CO2 in turtle bladder. Intracellular pH was continuously monitored by the fluorescent dye 6-carboxyfluorescein and exocytosis was monitored by the release of mucosal fluorescein dextran. The initial stimulation of H+ secretion by 1 or 5% CO2 added to the serosal solution was accompanied by a similar and temporally related increase in exocytosis.

Na-HCO3 cotransport and Na-H antiporter in chronic respiratory acidosis and alkalosis.

Renal acidification in renal proximal tubule is thought to be mediated by luminal Na-H antiporter and the HCO3- generated by this antiporter is removed from the cell by a basolateral Na-HCO3 cotransporter. To study the effect of respiratory acid-base disorders on these transport systems, we have measured the Na-HCO3 cotransport in basolateral membranes and Na-H antiporter in luminal membranes in control rabbits, rabbits exposed to 10% CO2 (chronic hypercapnia), and rabbits exposed to 10% O2-90% N2 (chronic hypocapnia). The Vmax of HCO3(-)-dependent 22Na uptake was significantly higher in chronic hypercapnia than controls (2.

Methyl isobutyl amiloride: a new probe to assess the number of Na-H antiporters.

We measured the binding of [3H]-5-(N-methyl-N-isobutyl) amiloride (MIA) to purified rabbit renal brush border membranes. MIA binding was protein, temperature and time dependent with optimal binding at pH 8.0 or above.

Phorbol-ester is bound specifically to renal luminal membranes and stimulates the Na-H antiporter.

We characterized binding of [3H]-phorbol-12,13-dibutyrate (an activator of protein kinase C) to highly purified rabbit cortical renal luminal membranes and measured its effect on the kinetics of the Na-H antiporter. There was 95% specific binding to luminal membranes and this binding was time, temperature and pH dependent with optimal binding at 4 degrees C and pH 7.4.

High affinity binding sites for epidermal growth factor (EGF) in renal membranes.

The kidney produces large quantities of EGF but the role of the kidney in binding and degradation of EGF is unknown. We studied 125I-EGF binding and degradation by highly purified cortical luminal and cortical basolateral membranes of rabbit renal cortex, and by medullary plasma membranes. Specific binding for 125I-EGF was found for the first time in cortical basolateral and medullary plasma membranes (60-80% of total binding) but not in cortical luminal membranes.

Effect of agents that alter cell calcium and microfilaments on CO2 stimulated H+ secretion in the turtle bladder.

CO2 addition to the serosal solution of turtle bladder stimulates H+ secretion. This stimulation of H+ secretion is thought to be mediated, at least in part, by exocytosis of vesicles containing H+ pumps that are inserted in the plasma membranes. In other systems, exocytosis is regulated by cell calcium and microfilaments.

Effect of metabolic or respiratory acidosis on rabbit renal medullary proton-ATPase.

Distal urinary acidification is thought to be mediated by an H+-ATPase sensitive to N-ethylmaleimide and dicyclohexyl-carbodiimide. We have studied the effect of chronic metabolic acidosis (NH4Cl for 3 days) or respiratory acidosis (inhalation of 10% CO2 for 2 days) on the H+-ATPase of plasma membranes prepared from the medulla. The enzymatic assay for the H+-ATPase was performed in the presence of ouabain and oligomycin and in the absence of Ca.

Na+-H+ antiporter in posthypercapnic state.

Posthypercapnic metabolic alkalosis has been attributed to decreased HCO3 excretion because of low glomerular filtration rate (GFR), volume contraction, or chloride depletion. We have previously shown that chronic hypercapnia enhances the Vmax of the Na+-H+ antiporter. We reasoned that an increased Vmax of the Na+-H+ antiporter could play a role in the maintenance of posthypercapnic metabolic alkalosis.

Chronic hypercapnia enhances Vmax of Na-H antiporter of renal brush-border membranes.

Chronic hypercapnia is associated with increased proximal HCO3 reabsorption that is thought to be mediated by a Na-H antiporter. We hypothesized that chronic hypercapnia would be associated either with increased Vmax or with decreased Km of the Na-H antiporter. To test this hypothesis we made rabbits hypercapnic for 48 h by exposure to 10% CO2.

Anion exchanger is present in both luminal and basolateral renal membranes.

Binding of the anion-exchange inhibitor 3H2-labeled 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) to highly purified luminal and basolateral beef kidney tubular membranes was characterized. Specific binding of [3H2]DIDS is present in both luminal and basolateral membranes. Scatchard analysis revealed a Kd for [3H2]DIDS of 5.

Intracellular pH of the turtle bladder assessed with fluorescent probes.

Intracellular pH of the turtle bladder was measured with fluorescent probe 6-carboxyfluorescein (6-CF) diacetate. In isolated cells this probe provides reliable, reproducible and fast measurements of intracellular pH. The probe was mainly located in the cytosol and thus the values of intracellular pH mainly reflect cytosolic pH.

Renal basolateral membrane Na-Ca exchange is electrogenic.

A Na-Ca exchange system is present in highly purified basolateral renal tubular membranes. In the present study we examined the electrogenicity of the system by measuring 45Ca uptake in the presence of favorable electric gradient created by K and valinomycin, by measuring the uptake of the lipophilic cation methytriphenylphosphonium (MTPP+) and by utilizing the voltage-sensitive dye DiS-C3(5). In the presence of an inward directed K gradient, 45Ca uptake in basolateral vesicles loaded with Na and suspended in K was significantly higher in the presence than in the absence of valinomycin.

Relationship of K and ammonia transport by the turtle bladder.

The relationship between K and ammonia transport was investigated in the turtle bladder. At serosal pH 6.4, ammonia transport is preferentially from serosa to mucosa and is, at least in part, mediated by NH4+ transport.

Plasma membrane proton ATPase from human kidney.

Distal urinary acidification is thought to be mediated by a proton ATPase (H+-ATPase). We isolated a plasma membrane fraction from human kidney cortex and medulla which contained H+-ATPase activity. In both the cortex and medulla the plasma membrane fraction was enriched in alkaline phosphatase, maltase, Na+,K+-ATPase and devoid of mitochondrial and lysosomal contamination.

Na-Ca exchange in renal tubular basolateral membranes.

We investigated the Na-dependent Ca transport in purified bovine luminal and basolateral renal tubular membranes. Na-dependent Ca uptake was observed in basolateral but not in luminal kidney tubular membranes. 45Ca uptake in basolateral membrane vesicles loaded with Na and suspended in K buffer was significantly greater than that observed in vesicles loaded with Na and suspended in Na buffer.

Partial purification and reconstitution of renal basolateral Na+-Ca2+ exchanger into liposomes.

The Na+-Ca2+ exchange system in renal tubular basolateral membranes was partially purified and incorporated into liposomes. Solubilization of basolateral membranes with 1% cholic acid in the presence of 2.5% soybean phospholipids and proteolytic treatment with Pronase (20 micrograms/ml) as described (Wakabayashi, S.

High-affinity calcium binding sites in luminal and basolateral renal membranes.

We evaluated Ca binding by highly purified luminal (L) and basolateral (BL) tubular membranes prepared from beef kidney. Ca binding was measured by using 45Ca and a rapid-filtration technique. After Ca uptake reached equilibrium, the vesicles were lysed and the amount of 45Ca retained in the membranes was considered the bound Ca.

Glucagon degradation by luminal and basolateral rabbit tubular membranes.

Glucagon is avidly degraded by the kidney, but the relative contribution of the luminal and basolateral tubular membranes to this process is unknown. We studied 125I-glucagon degradation by purified luminal (L) and basolateral (BL) tubular membranes prepared from rabbit kidney cortex, which showed enrichment vs. homogenate of marker enzyme activities (Na-K-ATPase for BL and maltase for L) of 10- and 14-fold, respectively.