Characterization of the cation-binding capacity of a potassium-adsorption filter used in red blood cell transfusion.

A K(+) -adsorption filter was developed to exchange K(+) in the supernatant of stored irradiated red blood cells with Na(+) . To date, however, the filter's adsorption capacity for K(+) has not been fully evaluated. Therefore, we characterized the cation-binding capacity of this filter. Artificial solutions containing various cations were continuously passed through the filter in 30 mL of sodium polystyrene sulfonate at 10 mL/min using an infusion pump at room temperature. The cation concentrations were measured before and during filtration. When a single solution containing K(+) , Li(+) , H(+) , Mg(2+) , Ca(2+) , or Al(3+) was continuously passed through the filter, the filter adsorbed K(+) and the other cations in exchange for Na(+) in direct proportion to the valence number. The order of affinity for cation adsorption to the filter was Ca(2+) >Mg(2+) >K(+) >H(+) >Li(+) . In K(+) -saturated conditions, the filter also adsorbed Na(+) . After complete adsorption of these cations on the filter, their concentration in the effluent increased in a sigmoidal manner over time. Cations that were bound to the filter were released if a second cation was passed through the filter, despite the different affinities of the two cations. The ability of the filter to bind cations, especially K(+) , should be helpful when it is used for red blood cell transfusion at the bedside. The filter may also be useful to gain a better understanding of the pharmacological properties of sodium polystyrene sulfonate.

The origin of idiopathic renal arteriovenous malformation with giant twin aneurysms.

A 50-year-old female patient who presented with intermittent gross hematuria was referred to our hospital. Three-dimensional computed tomography (3D-CT) revealed a left renal arteriovenous malformation (AVM). Because she declined to undergo additional therapy including surgical treatment, we observed the clinical course of renal AVM for 7 years using 3DCT. When the 3D-CT showed gradual enlargement of the aneurysms concurrent with the onset of clinical symptoms (cardiomegaly and hypertension), we performed simple left nephrectomy. After the operation, the cardiomegaly and hypertension returned to normal, and gross hematuria did not recur. Based on the macro-anatomical findings of the resected kidney and the observation of the natural course, this case strongly supported the hypothesis that the renal AVM had existed from birth and enlarged gradually to eventually produce the typical signs and symptoms.

Circumocular exanthema associated with chronic rejection after kidney transplantation.

A 43-year-old man had severe circumocular exanthema associated with chronic rejection 10 years after receiving a kidney transplant to treat end-stage renal failure. After the renal allograft was extracted, the exanthema diminished rapidly without any treatment. Donor-reactive immune cells seem to have cross-reacted with unknown pathogens on the skin and contributed to inflammation.

Transactivation of RON receptor tyrosine kinase by interaction with PDGF receptor beta during steady-state growth of human mesangial cells.

Although it is well known that platelet-derived growth factor (PDGF) causes mesangial cell proliferation (presumably contributing to progression of glomerular disease), targeted inhibition of the PDGF receptor system has shown only limited efficacy against glomerular diseases. To examine whether this discrepancy is due to the involvement of other pathways, we used phosphorylated receptor tyrosine kinase arrays and found that RON (recepteur d'origine nantais) was phosphorylated while the PDGF receptor was dephosphorylated (thus inactive) in human mesangial cells (HMCs) at the time of cell cycle entry. Further, RON remained active during steady-state growth. Activation of RON was independent of its canonical ligand, macrophage-stimulating protein, but was mediated by transactivation from the PDGF-engaged PDGF receptor. Following stimulation with PDGF we found that the two receptors physically interacted. Knockdown of RON by siRNA increased the number of apoptotic cells without affecting the rate of DNA synthesis, suggesting that RON has anti-apoptotic functions. Immunohistochemical analysis found phosphorylated RON in glomerular lesions of patients with IgA nephropathy but not those with minimal change nephrotic syndrome, a disease not associated with mesangial proliferation. These results suggest that RON is involved in mesangial cell proliferation under both physiological and pathological conditions, and may be a relevant target for therapeutic intervention.

Basolateral Na+/H+ exchange maintains potassium secretion during diminished sodium transport in the rabbit cortical collecting duct.

Stimulation of the basolateral Na(+)/K(+)-ATPase in the isolated perfused rabbit cortical collecting duct by raising either bath potassium or lumen sodium increases potassium secretion, sodium absorption and their apical conductances. Here we determined the effect of stimulating Na(+)/K(+)-ATPase on potassium secretion without luminal sodium transport. Acutely raising bath potassium concentrations from 2.5 to 8.5 mM, without luminal sodium, depolarized the basolateral membrane and transepithelial voltages while increasing the transepithelial, basolateral and apical membrane conductances of principal cells. Fractional apical membrane resistance and cell pH were elevated. Net potassium secretion was maintained albeit diminished and was still enhanced by raising bath potassium, but was reduced by basolateral ethylisopropylamiloride, an inhibitor of Na(+)/H(+) exchange. Luminal iberitoxin, a specific inhibitor of the calcium-activated big-conductance potassium (BK) channel, impaired potassium secretion both in the presence and absence of luminal sodium. In contrast, iberitoxin did not affect luminal sodium transport. We conclude that basolateral Na(+)/H(+) exchange in the cortical collecting duct plays an important role in maintaining potassium secretion during compromised sodium supplies and that BK channels contribute to potassium secretion.

Peritoneal injury by methylglyoxal in peritoneal dialysis.

BACKGROUND: Peritonealdialysis (PD) is a common treatment for patients with reduced or absent renal function. Long-term PD leads to peritoneal injury with structural changes and functional decline, such as ultrafiltration loss. At worst, peritoneal injury leads to encapsulating peritoneal sclerosis, a serious complication of PD. Glucose degradation products contained in PD fluids contribute to the bioincompatibility of conventional PD fluids. Methylglyoxal (MGO) is an extremely toxic glucose degradation product. The present study examined the injurious effect of MGO on peritoneum in vivo. METHODS: Male Sprague-Dawley rats (n = 6) were administered PD fluids (pH 5.0) containing 0, 0.66, 2, 6.6, or 20 mmol/L MGO every day for 21 days. On day 22, peritoneal function was estimated by the peritoneal equilibration test. Drained dialysate was analyzed for type IV collagen-7S, matrix metalloproteinase (MMP), and vascular endothelial growth factor (VEGF). Histological analysis was also performed. RESULTS: In rats receiving PD fluids containing more than 0.66 mmol/L MGO, peritoneal function decreased significantly and levels of type IV collagen-7S and MMP-2 in drained dialysate increased significantly. In the 20-mmol/L MGO-treated rats, loss of body weight, expression of VEGF, thickening of the peritoneum, and formation of abdominal cocoon were induced. MMP-2 and VEGF were produced by infiltrating cells in the peritoneum. Type IV collagen was detected in basement membrane of microvessels. CONCLUSION: MGO induced not only peritoneal injury but also abdominal cocoon formation in vivo. The decline of peritoneal function may result from reconstitution of microvessel basement membrane or neovascularization.

Effect of trimethoprim-sulfamethoxazole on Na and K+ transport properties in the rabbit cortical collecting duct perfused in vitro.

BACKGROUND: In this study, the membrane mechanisms of hyperkalemia caused by trimethoprim-sulfamethoxazole (TMP-SMX) combination antibiotics were assessed in the cortical collecting duct (CCD). METHODS: We used the microelectrode technique and flux measurements, and examined the effects of TMP and SMX on electrical properties of the apical and basolateral membranes in the rabbit CCD perfused in vitro. RESULTS: TMP in the lumen caused increases in apical membrane voltage, fractional apical membrane resistance (fRA), and transepithelial resistance (RT), all effects which were completely inhibited by luminal amiloride, but not by luminal Ba2+. The luminal TMP inhibited both net Na+ reabsorption and K+ secretion in the CCD. TMP in the bath slightly but significantly depolarized transepithelial voltage and basolateral membrane voltage without influencing fRA or RT. SMX in the lumen or bath had no effect on barrier voltages or resistances. CONCLUSION: TMP mainly acts on the apical membrane of the CCD, inhibits the amiloride-sensitive macroscopic Na+ conductance in this membrane, and thereby decreases the net driving force for K+ exit across the membrane, resulting in an inhibition of K+ secretion. SMX in the lumen or bath had no effect on the CCD.

Mechanisms for nongenomic and genomic effects of aldosterone on Na+/H+ exchange in vascular smooth muscle cells.

OBJECTIVES: We have reported that exposure of vascular smooth muscle cells (VSMCs) to aldosterone for 3 and 24 h activated Na+/H+ exchange (NHE) via nongenomic and genomic mechanisms, respectively. The present study determined whether aldosterone-induced nongenomic and genomic NHE activation depends on the number of transporters, the turnover rate of a single transporter, and/or the change in intracellular pH (pHi) sensitivity of the transporter, and whether aldosterone-induced NHE activation is inhibited by the selective mineralocorticoid receptor (MR) antagonist (eplerenone). METHODS: Using a fluorescent dye, we assessed NHE activity by Na-dependent acid extrusion rates (JH) after an acid load in the absence of CO2/HCO3- in VSMCs treated with aldosterone. RESULTS: Treatment with aldosterone for 3 and 24 h increased JH at the wide pHi range, and shifted the JH versus pHi in the alkaline direction. Without affecting the apparent Km for external Na+, the Vmax increased in VSMCs treated with aldosterone for 3 and 24 h. Both eplerenone and spironolactone inhibited only aldosterone-induced genomic NHE activation, but the IC50 of eplerenone was smaller than that of spironolactone. CONCLUSION: We demonstrated that: (1) both nongenomic and genomic stimulatory effects of aldosterone on NHE activity in VSMCs occur by an increase in the number of NHEs and the alkaline shift in pHi sensitivity of the NHE; (2) only the aldosterone-induced genomic NHE activation occurs via MR; and (3) both eplerenone and spironolactone inhibit the aldosterone-induced genomic NHE activation, but eplerenone is more effective than spironolactone, based on the IC50 value in VSMCs.

A case of encapsulating peritoneal sclerosis at the clinical early stage with high concentration of matrix metalloproteinase-2 in peritoneal effluent.

In encapsulating peritoneal sclerosis (EPS), matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases are involved in the remodeling of peritoneal tissue. We measured the MMP-2 concentration in the peritoneal effluents of a patient with EPS who discontinued continuous ambulatory peritoneal dialysis (CAPD) therapy because of ultrafiltration failure and/or underdialysis. First, we report a 58-year-old female patient who discontinued CAPD therapy because of underdialysis. Several months after cessation of CAPD, she complained of slightly blood-colored ascites and had an elevated level of C-reactive protein (CRP) in plasma. She was diagnosed as having clinical early-stage EPS. Peritoneal effluents drained from this case, and from 11 patients who discontinued CAPD therapy because of ultrafiltration failure and/or underdialysis, and who underwent peritoneal lavage with 1.5% dextrose peritoneal dialysis fluid for several months, were analyzed by gelatin zymography. MMP-2 concentration was also measured by enzyme-linked immunosorbent assay (ELISA). MMP-2 concentration in peritoneal effluent of this patient was highest compared with that of the other patients. There was some tendency of a positive correlation between MMP-2 concentration per 1 g protein and D/Pcr, and was negative correlation between MMP-2 concentration per 1 g of protein and D/D0 glucose. We concluded that MMP-2 is involved in the peritoneal remodeling of long-term CAPD therapy and the progression of EPS.

[Effect of oral intake of an enteric capsule preparation containing Bifidobacterium longum on the progression of chronic renal failure].

Since the accumulation of intestinal putrefactive products, such as indole and phenol, is known to play a role in the exacerbation of chronic renal failure, reduction of these intestinal putrefactive products can be expected to retard the progression of renal failure. In the present study, an enteric capsule preparation containing Bifidobacterium longum(Bifidus HD) was administered orally to 27 patients with chronic renal failure(CRF) for 6 months. Though no significant effect was found in the whole group, a significant retardation of the progression of renal failure was found in patients with an initial serum creatinine level > or = 4.0 mg/dl or those with an initial serum inorganic phosphate level > or = 4.0 mg/dl. There was no adverse effect observed in any case. Bifidus HD is considered a useful tool for suppressing the progression of chronic renal failure(CRF) in the conservative period.

Hyperosmotic urea activates basolateral NHE in proximal tubule from P-gp null and wild-type mice.

Using the pH-sensitive fluorescent dye BCECF, we compared the effects of hyperosmotic urea on basolateral Na(+)/H(+) exchange (NHE) with those of hyperosmotic mannitol in isolated nonperfused proximal tubule S2 segments from mice lacking both the mdr1a and mdr1b genes (KO) and wild-type (WT) mice. All the experiments were performed in CO(2)/HCO-free HEPES solutions. Osmolality of the peritubular solution was raised from 300 to 500 mosmol/kgH(2)O by adding mannitol or urea. NHE activity was assessed by the Na(+)-dependent acid extrusion rate (J(H)) after an acid load with NH(4)Cl prepulse. In WT mice, hyperosmotic mannitol had no effect on J(H) at over the entire range of intracellular pH (pH(i)) studied (6.20-6.90), whereas in KO mice it increased J(H) at a pH(i) range of 6.20-6.45. In contrast, in both WT and KO mice, hyperosmotic urea increased J(H) at a pH(i) range of 6.20-6.90. In KO mice, J(H) in a hyperosmotic urea solution were similar to those in a hyperosmotic mannitol solution at a pH(i) range of 6.20-6.40 but were greater than in a hyperosmotic mannitol solution at a pH(i) range of 6.45-6.90. In WT mice, hyperosmotic urea caused an increase in V(max) without changing K(m) for peritubular Na(+). Staurosporine (the PKC inhibitor) inhibited hyperosmotic mannitol-induced NHE activation in KO mice, whereas it had no effect on hyperosmotic urea-induced NHE activation in WT or KO mice. Genistein (the tyrosine kinase inhibitor) inhibited hyperosmotic urea-induced NHE activation in WT and KO mice, whereas it caused no effect on hyperosmotic mannitol-induced NHE activation in KO mice. We conclude that hyperosmotic urea activates basolateral NHE via tyrosine kinase in tubules from both WT and KO mice, whereas hyperosmotic mannitol activates it via PKC only in tubules from KO mice.

Hyperosmotic mannitol activates basolateral NHE in proximal tubule from P-glycoprotein null mice.

Using the pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, we examined the effects of hyperosmotic mannitol on basolateral Na(+)/H(+) exchange (NHE) activity in isolated nonperfused proximal tubule S2 segments from mice lacking both the mdr1a and mdr1b genes (KO) and wild-type mice (WT). All experiments were performed in CO(2)/HCO-free HEPES solutions. Osmolality of the peritubular solution was raised from 300 to 500 mosmol/kgH(2)O by the addition of mannitol. NHE activity was assessed by Na(+)-dependent acid extrusion rates (J(H)) after an acid load with NH(4)Cl prepulse. Under isosmotic conditions, J(H) values at a wide intracellular pH (pH(i)) range of 6.20-6.90 were not different between the two groups. In WT mice, hyperosmotic mannitol had no effect on J(H) at the wide pH(i) range. In contrast, in KO mice, hyperosmotic mannitol increased J(H) at a pH(i) range of 6.20-6.45 and shifted the J(H)-pH(i) relationship by 0.15 pH units in the alkaline direction. In KO mice, hyperosmotic mannitol caused an increase in maximal velocity without changing the Michaelis-Menten constant for peritubular Na(+). Exposure of cells from WT mice to the hyperosmotic mannitol solution including the P-gp inhibitor cyclosporin A increased J(H) (at pH(i) 6.30) to an extent similar to that in cells from KO mice exposed to hyperosmotic mannitol alone. In KO mice, staurosporine and calphostin C inhibited the hyperosmotic mannitol-induced increase in J(H). The stimulatory effect of hyperosmotic mannitol on J(H) was mimicked by addition to the isosmotic control solution, including phorbol 12-myristate 13-acetate (PMA; the PKC activator). In WT mice, hyperosmotic mannitol with PMA increased J(H). We conclude that, in the absence of P-gp activity, hyperosmotic mannitol activates basolateral NHE via protein kinase C, whereas in the presence of P-gp activity, it does not.

P-gp-induced modulation of regulatory volume increase occurs via PKC in mouse proximal tubule.

The present study examined the role of protein kinase C (PKC) in the P-glycoprotein (P-gp)-induced modulation of regulatory volume increase (RVI) in the isolated nonperfused proximal tubule S2 segments from mice lacking both mdr1a and mdr1b genes (KO) and wild-type (WT) mice. The hyperosmotic solution (500 mosmol/kgH(2)O) involving 200 mM mannitol activated PKC and elicited RVI in the tubules from KO mice but not from WT mice. The addition of the hyperosmotic solution including the PKC activator phorbol 12-myristate 13-acetate (PMA) to the tubules of the WT mice activated PKC and elicited RVI. The hyperosmotic solution in the presence of the P-gp inhibitors (verapamil or cyclosporin A) elicited RVI in the tubules from the WT mice but not from the KO mice. The PMA- and the P-gp inhibitors-induced RVI was abolished by cotreatment with the PKC inhibitors (staurosporine or calphostin C). In the tubules of the KO mice, the PKC inhibitors abolished RVI, but PMA did not. In the tubules of the WT mice, the microtubule disruptor (colchicine), the microfilament disruptor (cytochalasin B), the phosphatidylinositol 3-kinase (PI 3-kinase) blocker (wortmannin), but not another PI 3-kinase blocker (LY-294002), inhibited the PMA-induced RVI. In the tubules of the KO mice, colchicine, cytochalsin B, and wortmannin abolished RVI, but LY-294002 did not. We conclude that 1) in the mouse proximal tubule, P-gp-induced modulation of RVI occurs via PKC; and 2) the microtubule, microfilament, and wortmannin-sensitive, LY-294002-insensitive PI 3-kinase contribute to the PKC-induced RVI.