PubMed Health⌕ Search

Biomedical subjects

B A Molitoris

Publications and source records attributed to B A Molitoris.

At least 73 records · Page 4Linked to original sources
PubMed1989

The role of aluminum in the pathogenesis of anemia in an outpatient hemodialysis population.

Anemia is a well-defined complication of aluminum overload in chronic dialysis patients which may be present before other manifestations of aluminum toxicity are obvious. Causes of anemia in chronic renal failure are multiple, and at the present time there is no marker for aluminum-induced anemia. Deferoxamine (DFO) treatment can correct aluminum-related anemia and microcytosis, but may be associated with side effects. Because of the possible role of aluminum in red blood cells in causing the anemia associated with aluminum overload, we attempted to test red blood cell (RBC) aluminum as a marker for aluminum-associated anemia and to assess the prevalence of aluminum-associated anemia in an outpatient dialysis population. Both random plasma aluminum and RBC aluminum correlated well with the increase in plasma aluminum seen following DFO challenge. However, RBC aluminum was affected less by changes in oral aluminum intake than plasma aluminum. There were strong correlations of RBC and plasma aluminum to corpuscular volume (MCV) in our patients. Moreover, patients within the highest quartile of RBC aluminum had a lower mean MCV (82.1 +/- 1.7 vs 89.6 +/- 1.7, p less than .01) and hematocrit (HCT) (24.3 +/- 4 vs 28.2 +/- 1.5, p less than .05) than those within the lowest quartile. These data suggest that aluminum toxicity is an important cause of microcytic anemia in outpatient hemodialysis patients. Prospective long-term studies are needed to further define the usefulness of RBC aluminum in diagnosing and following hemodialysis patients with aluminum-induced anemia.

Aluminum↗
PubMed1988

Characterization of ischemia-induced loss of epithelial polarity.

Total renal ischemia for various time intervals (0-50 min) resulted in the rapid and duration-dependent redistribution of polarized membrane lipids and proteins in renal proximal tubule cells. Following only 15 min of ischemia, apical membrane enrichment of NaK-ATPase, normally a basolateral membrane (BLM) enzyme, had increased (1.6 +/- 0.6 vs. 2.9 +/- 1.2, P less than 0.01). In vivo histochemical localization of NaK-ATPase showed reaction product throughout the apical microvillar region. PTH-stimulatable adenylate cyclase, another BLM protein, was also found in ischemic but not control apical membrane fractions. One dimensional SDS-PAGE showed four bands, present in control BLM and ischemic apical membranes, which could not be found in control apical membrane fractions. Immunohistochemical localization of leucine aminopeptidase (LAP) showed the enzyme was limited to the apical domain in control cells. Following ischemic injury (50 min), LAP staining could be seen within the cell and along the BLM. Following 24 hr of reperfusion, the BLM distribution of LAP was further enhanced. With cellular recovery from ischemic injury (5 days), LAP was again only visualized in the apical membrane. Duration-dependent alterations in apical and BLM lipids were also observed. Apical sphingomyelin and phosphatidylserine and the cholesterol-to-phospholipid ratio decreased rapidly while apical phosphatidylcholine and phosphatidylinositol increased. Taken together, these results indicate renal ischemia causes rapid duration-dependent reversible loss of surface membrane polarity in proximal tubule cells.

Adenylyl Cyclases↗
PubMed1988

Rapid removal of DFO-chelated aluminum during hemodialysis using polysulfone dialyzers.

Aluminum (Al) removal following deferoxamine (DFO) therapy in hemodialysis patients was evaluated in a paired-fashion comparing cuprophane (Travenol 12.11) and polysulfone (Fresenius F-80) dialyzers. QB and QD were held constant at 250 and 500 ml/min, respectively. The polysulfone dialyzer increased total plasma Al clearance from 20.0 +/- 2.8 to 80.5 +/- 7.6 ml/min (P less than 0.01), and reduced the t 1/2 of plasma Al during hemodialysis from 538 +/- 113 to 112 +/- 12 min (P less than 0.01). The polysulfone F-80 dialyzer increased Al removal during the first hour of hemodialysis from 518 +/- 191 to 1812 +/- 720 micrograms/hr (P less than 0.01). During a four hour hemodialysis the F-80 dialyzer returned plasma Al levels to pre-DFO values (103 +/- 36 vs. 93 +/- 23, P less than 0.05), suggesting complete removal of the DFO chelated Al complex. In one patient Al removal was evaluated using cuprophane, F-40, F-60 and F-80 dialyzers and the t 1/2 for Al removed decreased from 484.6 to 276.1 and 108 to 99 minutes, respectively. These data show the Fresenius F-80 polysulfone dialyzer effects the rapid removal of DFO-Al complexes. We propose use of the Fresenius F-80 dialyzer in conjunction with reduced DFO doses and i.m. administration of DFO the day prior to dialysis to limit DFO exposure as a method to decrease DFO-related side-effects in hemodialysis patients.

Aluminum↗
PubMed1987

Static and dynamic components of renal cortical brush border and basolateral membrane fluidity: role of cholesterol.

Static polarization and differential polarized phase fluorimetry studies on rat renal cortical brush border (BBM) and basolateral membranes (BLM) were undertaken to determine the membrane components responsible for differences in BBM and BLM fluidity, whether these differences were due to the order or dynamic components of membrane fluidity and if a fluidity gradient existed within the bilayer. Surface membrane proteins rigidified both BBM and BLM fluidity. Neutral lipid extraction, on the other hand, caused a larger decrease in BBM than BLM fluorescence polarization (0.104 vs. 0.60, P less than 0.01) using diphenyl hexatriene (DPH). Cholesterol addition to phospholipid fractions restored membrane fluidity to total lipid values in both BBM and BLM phospholipids. The response to cholesterol in the BBM was biphasic, while the BLM response was linear. Lateral mobility, quantitated using dipyrenylpropane, was similar in both BBM and BLM fractions at 35 degrees C. BBM and BLM differed primarily in the order component of membrane fluidity as DPH-limiting anisotropy (r infinity) (0.212 vs. 0.154, P less than 0.01) differed markedly between the two membrane fractions. The two membrane components also differed with respect to 2 and 12-anthroyloxy stearate (2-AS, 12-AS) probes, indicating a difference in the dynamic component of membrane fluidity may also be present. DPH and 12-AS probes were also used to quantitate inner core membrane fluidity and showed the BBM was less fluid than the BLM for intact membranes, total lipid extracts and phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Efficacy of intramuscular and intraperitoneal deferoxamine for aluminum chelation.

As intravenous administration of deferoxamine is difficult in home dialysis patients we set out to determine the efficacy of intramuscular (i.m.) and intraperitoneal (i.p.) deferoxamine for removal of aluminum. Patients with serum aluminum levels greater than 90 micrograms/liter were studied in a paired fashion with each patient serving as their own control. Serum and peritoneal fluid aluminum were determined using flameless atomic absorption. In hemodialysis patients 2 g of intravenous deferoxamine increased serum aluminum from 124.7 +/- 32.4 to 415 +/- 192.4 micrograms/liter. One g of deferoxamine given intravenously or intramuscularly resulted in 76.8 +/- 35.3% and 70.4 +/- 23.2%, respectively, of the 2 g i.v. response. The rate at which serum aluminum increased following i.v. deferoxamine infusion was biphasic, with an initial rapid phase lasting 139 minutes followed by a much slower phase. The volume of distribution of aluminum following deferoxamine administration was 12.6 +/- 1.61 and the half life (t1/2) for aluminum removal during hemodialysis was 9.0 +/- 2.0 hours. The increase in serum aluminum following deferoxamine was not due to chelation of erythrocyte aluminum as erythrocyte aluminum remained constant over 24 hours. In patients on continuous ambulatory peritoneal dialysis, 2 g intravenous deferoxamine resulted in the removal of 560 +/- 267 micrograms of aluminum over 24 hours while 2 g deferoxamine given intraperitoneally gave 91 +/- 13% of the intravenous response. Aluminum clearance over 48 hours was twice that for 24 hours for both i.v. and i.p. deferoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗
PubMed1987

Effects of vitamin D-induced chronic hypercalcemia on rat renal cortical plasma membranes and mitochondria.

Increases in intracellular and mitochondrial calcium content that accompany ischemic and toxic acute renal failure have been suggested to mediate renal tubular cell injury and dysfunction, but the mechanism(s) are unknown. We studied the effects of in vivo vitamin D-induced chronic hypercalcemia on rat renal cortical brush-border and basolateral membranes and mitochondria. In the brush-border membrane, hypercalcemia caused significant decreases in alkaline phosphatase-specific activity, total phospholipid molar content, and phosphatidylserine percent molar composition and increases in the cholesterol-to-total phospholipid molar ratio and phosphatidylinositol percent molar composition. In the basolateral membrane, hypercalcemia caused significant decreases in Na+-K+-ATPase-specific activity and total phospholipid molar content and increases in the cholesterol-to-total phospholipid molar ratio and phosphatidylinositol 4,5-bisphosphate percent molar composition. In the mitochondria, hypercalcemia caused a mild increase in the mitochondrial calcium content, but no alterations in succinic dehydrogenase-specific activity, succinate-, ADP-, or uncoupler-induced respiration. Thus hypercalcemia caused alterations in brush-border and basolateral membrane enzyme activity and lipid composition, but no functional changes were detected in mitochondria. These hypercalcemia-induced plasma membrane biochemical alterations may be markers of early cell injury and suggest a role for calcium in causing or predisposing to renal tubular cell injury.

Animals↗
PubMed1987

Ischemia induces surface membrane dysfunction. Mechanism of altered Na+-dependent glucose transport.

Reversible ischemia reduced renal cortical brush border membrane (BBM) Na+-dependent D-glucose uptake (336 +/- 31 vs. 138 +/- 30 pmol/mg per 2 s, P less than 0.01) but had no effect on Na+-independent glucose or Na+-dependent L-alanine uptake. The effect on D-glucose uptake was present after only 15 min of ischemia and was due to a reduction in maximum velocity (1913 +/- 251 vs. 999 +/- 130 pmol/mg per 2 s; P less than 0.01). This reduction was not due to more rapid dissipation of the Na+ gradient, altered sidedness of the vesicles, or an alteration in membrane potential. Ischemia did, however, reduce the BBM sphingomyelin-to-phosphatidylcholine (SPH/PC) and cholesterol-to-phospholipid ratios and the number of specific high-affinity Na+-dependent phlorizin binding sites (390 +/- 43 vs. 146 +/- 24 pmol/mg; P less than 0.01) without altering the binding dissociation constant (Kd). 20 mM benzyl alcohol also reduced the number of Na+-dependent phlorizin binding sites (418 +/- 65 vs. 117 +/- 46; P less than 0.01) without altering Kd. The reduction in Na+-dependent D-glucose transport correlated with ischemic-induced changes in the BBM SPH/PC and cholesterol-to-phospholipid ratios and membrane fluidity. Taken together these data indicate the cellular site responsible for ischemic-induced reduction in renal cortical transcellular glucose transport is the BBM. We propose the mechanism involves marked alterations in BBM lipids leading to large increases in BBM fluidity which reduces the binding capacity of Na+-dependent glucose carriers. These data indicate that reversible ischemia has profound effects on the surface membrane function of epithelial cells.

Animals↗
PubMed1987

Bilateral congenital renal arteriovenous fistulas.

Bilateral renal arteriovenous (AV) fistulas were discovered in a patient with refractory hypertension. The lesion in the right kidney appeared to be congenital, whereas the etiology of the left-sided lesion could not be determined. Ablation of both fistulas effected a significant decrease in blood pressure. The angiographic appearance of a renal AV fistula often reveals its cause. These fistulas can cause significant morbidity. A review of 49 cases of congenital renal AV fistulas reveals that most are found in women and in the right kidney. Bilateral renal AV fistulas have not been previously described. Hypertension commonly develops in patients with renal AV fistulas and may resolve or improve upon fistula ablation. Improvement in blood pressure after fistula ablation occurs more frequently in traumatic fistulas than in congenital ones. Although the pathophysiology of hypertension is felt to be the shunting of the blood flow by the fistula from the renal parenchyma and subsequent stimulation of the renin system, renal vein renin sampling may be of little diagnostic value.

Arteriovenous Malformations↗
PubMed1986

Maintenance of epithelial surface membrane lipid polarity: a role for differing phospholipid translocation rates.

Large differences in lipid composition of apical and basolateral membranes from epithelial cells exist. To determine the responsible mechanism(s), rat renal cortical brush border and basolateral membrane phospholipids were labeled using 32P and either [3H]-glycerol or [2-3H] acetate for incorporation and degradation studies, respectively. Brush border and basolateral membrane fractions were isolated simultaneously from the same cortical homogenate. Different phospholipid classes were degraded at variable rates with phosphatidylcholine having the fastest decay rate. Decay rates for individual phospholipid classes were, however, similar in both brush border and basolateral membrane fractions. In phospholipid incorporation studies, again, large variations existed between individual phospholipid classes with phosphatidylcholine and phosphatidylinositol showing the most rapid rates of incorporation. Sphingomyelin and phosphatidylserine showed extremely slow incorporation rates and did not enter into the isotopic decay phase for 48 hr. In contrast to degradation studies, however, the same phospholipid class labeled the two surface membrane domains at highly variable rates. The difference in these rates, with the exception of phosphatidylinositol, were identical to the differences in phospholipid compositions between the two membranes. For example, phosphatidylcholine was incorporated into the basolateral membrane 2.5 X faster than into the brush border membrane and its relative composition was 2.5 X greater in the basolateral membrane. The opposite was true for sphingomyelin. These results indicate incorporation and not degradation rates of individual phospholipids play a major role in regulating the differing phospholipid composition of brush border and basolateral membranes.

Animals↗
PubMed1986

Therapeutic drug monitoring in patients with chronic renal failure: evaluation of the Abbott TDx drug assay system.

Immunoassay techniques have been widely used for therapeutic drug monitoring, but lack of antibody specificity can lead to measurement of erroneous drug concentrations due to cross-reactivity with other drugs, metabolites, or endogenous substances, particularly in patients with excretory organ compromise such as renal dysfunction. The Abbott TDx system, a popular automated immunoassay method for therapeutic drug monitoring, was used to measure apparent serum concentrations of carbamazepine, digoxin, gentamicin, lidocaine, phenobarbital, phenytoin, quinidine, valproic acid, and vancomycin in patients with renal failure who were not receiving these drugs. Endogenous substances and other concomitantly administered drugs did not lead to spuriously elevated drug levels, and a previous report of cross-reactive digoxin-like substances was not confirmed. Pooled plasma samples from the patients were spiked with digoxin or phenytoin, each at two concentrations, and the samples were assayed for the drug concentration using the TDx system. No falsely elevated values were found. This work suggests that the TDx system may be better suited for the measurement of these drugs in patients with renal failure than some other immunoassay methods.

Carbamazepine↗
PubMed1985

Renal cortical brush-border and basolateral membranes: cholesterol and phospholipid composition and relative turnover.

A new procedure for the rapid isolation of renal cortical brush-border and basolateral membranes from the same homogenate is described. Brush-border membranes isolated using Mg2+-EGTA precipitation were enriched 18-fold for leucine aminopeptidase and had a recovery of 32.5%. Basolateral membrane fractions were isolated using a discontinuous sucrose gradient and showed an enrichment of 10.7-fold and recovery of 12.8% using (Na+,K+)-ATPase as a marker enzyme. Lipid analysis using two-dimensional TLC separation of phospholipids and gas liquid chromatography for cholesterol showed marked differences in the lipid composition of the brush-border and basolateral membranes. The brush-border membrane had increased sphingomyelin, phosphatidylserine, ethanolamine plasmalogens, and an increased cholesterol-to-phospholipid and sphingomyelin-to-phosphatidylcholine ratio compared to the basolateral membrane. The relative turnover of total membrane and individual phospholipid species using a double isotope ratio method was carried out. Phospholipids were labeled with either phosphorus 32 and 33 or acetate (3H, 1-14C). The relative turnover of phospholipid species and cholesterol differed strikingly. Phosphatidylcholine showed a high turnover, phosphatidylethanolamine and phosphatidylinositol had intermediate values and sphingomyelin, phosphatidylserine and cholesterol had low relative turnover rates. The order of phospholipid class relative turnover was independent of the labeled precursor used. The brush-border membrane had a significantly reduced relative turnover rate for total membrane phospholipids, sphingomyelin and cholesterol compared to the basolateral membrane. These data show marked differences in the lipid composition and relative turnover rates of the phospholipid species of the brush-border and basolateral membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Renal apical membrane cholesterol and fluidity in regulation of phosphate transport.

Renal proximal tubule cells adapt to dietary phosphate (Pi) restriction by increasing Pi transport independent of parathyroid hormone, vitamin D metabolites, or serum Ca2+. To determine the underlying cellular mechanism(s), brush border (BBM) and basolateral membranes (BLM) were isolated from growing male rats fed a synthetic diet containing variable levels of Pi (0.1-1.4%). Dietary Pi restriction was without effect on either BBM or BLM total lipid phosphorus, individual phospholipid species, or BLM Na+-K+-ATPase specific activity. However, dietary Pi restriction (0.1 vs. 1.0%) did cause a significant reduction in BBM but not BLM cholesterol (0.45 vs. 0.41 mumol/mg protein). Brush border membrane cholesterol was inversely correlated with the tubular reabsorption of Pi (r = 0.77, P less than 0.01) over a broad range (99.9-46.2%). Arrhenius analysis of two intrinsic BBM enzymes revealed a significant reduction in the breakpoint temperature for alkaline phosphatase but no change for Mg2+-ATPase. Fluorescence polarization studies showed increased BBM inner core fluidity due to an alteration in neutral lipids but not phospholipid, fatty acid, or protein membrane components. These data demonstrate that the BBM can regulate its cholesterol content independent of the BLM. Furthermore, they suggest that adaptation to dietary Pi restriction involves a reduction in BBM cholesterol, which may be mediated by an increase in membrane fluidity.

Adenosine Triphosphatases↗
PubMed1985

Ischemia induces partial loss of surface membrane polarity and accumulation of putative calcium ionophores.

To determine if ischemia induces alterations in renal proximal tubule surface membranes, brush border (BBM) and basolateral membranes (BLM) were isolated simultaneously from the same cortical homogenate after 50 min of renal pedicle clamping. Ischemia caused a selective decrease in the specific activity of BBM marker enzymes leucine aminopeptidase and alkaline phosphatase, but did not effect enrichment (15 times). Neither specific activity nor enrichment (10 times) of BLM NaK-ATPase was altered by ischemia. Contamination of BBM by intracellular organelles was also unchanged, but there was an increase in the specific activity (41.1 vs. 60.0, P less than 0.01) and enrichment (2.3 vs. 4.3, P less than 0.01) of NaK-ATPase in the ischemic BBM fraction. Ischemia increased BLM lysophosphatidylcholine (1.3 vs. 2.5%, P less than 0.05) and phosphatidic acid (0.4 vs. 1.3%, P less than 0.05). Ischemia also decreased BBM sphingomyelin (38.5 vs. 29.6%, P less than 0.01) and phosphatidylserine (16.1 vs. 11.4%, P less than 0.01), and increased phosphatidylcholine (17.2 vs. 29.7%, P less than 0.01), phosphatidylinositol (1.8 vs. 4.6%, P less than 0.01), and lysophosphatidylcholine (1.0 vs. 1.8%, P less than 0.05). The large changes in BBM phospholipids did not result from new phospholipid synthesis, since the specific activity (32P dpm/nmol Pi) of prelabeled individual and total phospholipids was unaltered by ischemia. We next evaluated if these changes were due to inability of ischemic cells to maintain surface membrane polarity. Cytochemical evaluation showed that while NaK-ATPase could be detected only in control BLM, specific deposits of reaction product were present in the BBM of ischemic kidneys. Furthermore, using continuous sucrose gradients, the enzymatic profile of ischemic BBM NaK-ATPase shifted away from ischemic BLM NaK-ATPase and toward the BBM enzymatic marker leucine aminopeptidase. Taken together, these data suggest that NaK-ATPase activity determined enzymatically and cytochemically was located within ischemic BBM. We propose that ischemia impairs the ability of cells to maintain surface membrane polarity, and also results in the accumulation of putative calcium ionophores.

Animals↗
PubMed1984

A statistical method for determining the breakpoint of two lines.

A method is presented for determining the breakpoint of a line which suddenly changes slope at some unknown point. A statistical test is given for testing whether the broken line is a significantly better fit to the data than a single straight line. An approximate confidence interval can be obtained for the position of the breakpoint.

Alkaline Phosphatase↗
PubMed1980

Concentration of myo-inositol in skeletal muscle of the rat occurs without active transport.

The cellular uptake of nonphosphorylated myo-inositol (MI) and its incorporation into phosphoinositide in the rat epitrochlearis muscle was measured. Cellular uptake of [2-(3)H]MI was determined by the difference between total uptake and [2-(3)H]MI present in the extracellular fluid determined with [1-(14)C]mannitol. Cellular uptake was parabolic and directly proportional to medium MI concentrations between 25 and 3,200 muM. Saturation of a MI carrier was not evident. Moreover, uptake was not inhibited by 2 mM ouabain, 0.3 mM 2,4-dinitrophenol, or 22 mM glucose. Insulin, 100 mU/ml, was without effect on either cellular uptake of [2-(3)H]MI or its incorporation into phosphoinositides. In muscles that were preloaded with [2-(3)H]MI and then incubated in media that contained a constant amount of MI but no [2-(3)H]MI, 44.3% of the [2-(3)H]MI was released after 10 min increasing to 62.5% by 120 min. Cellular MI concentrations were 0.18 mumol/g wet tissue (four times plasma levels) in rapidly isolated and frozen epitrochlearis muscle. When muscle was incubated without MI, 48% of endogenous MI was lost rapidly. Restoration of cellular MI in 50 muM MI media occurred in two phases, a rapid uptake phase lasting 10 min and a subsequent slow phase of MI uptake. It is concluded that MI enters and leaves skeletal muscle cells freely by a process that does not involve active transport. Neither insulin nor hyperglycemia affected MI transport nor its incorporation into phosphoinositides. The intracellular to medium concentration gradient may be dependent on reversible binding to tubulin and possibly to other intracellular components.

Adenosine Triphosphate↗
PubMed1979

Effects of glucose and parathyroid hormone on the renal handling of myoinositol by isolated perfused dog kidneys.

The effects of glucose and parathyroid hormone (PTH) on the transport and metabolism of myoinositol (MI) and [2-(3)H]MI were studied in isolated perfused dog kidneys. Studies during perfusion of kidneys with normal and elevated glucose concentrations demonstrated that under normal conditions the isolated kidney reabsorbed 94.7+/-0.2% of the filtered MI, and the renal production of (3)H-metabolities of MI was 117.9+/-6% of the filtered MI load. This indicated that entry of MI into tubular cells by reabsorption was not the sole pathway for entry into the pool of MI within the kidney undergoing catabolism. High glucose perfusate decreased MI reabsorption to 68.6+/-4.7% and thus decreased delivery of [2-(3)H]MI into the catabolic pool from the reabsorptive pathway. In the high glucose experiments, the rate of [2-(3)H]MI catabolism exceeded [2-(3)H]MI reabsorption by the same fraction as in normal glucose experiments, which indicates that high glucose did not affect nonreabsorptive access of MI to the catabolic site. In contrast to the effects of glucose, PTH administration resulted in an increase in perfusate MI concentration and a decrease in the perfusate [2-(3)H]MI specific activity. Concomitantly, urinary MI and [2-(3)H]MI concentrations were increased, again with a decrease in [2-(3)H]MI specific activity. These results indicate that PTH caused a release of MI into the urine (not the same as decreased MI reabsorption, which would not affect urinary [(3)H]MI specific activity) and into the perfusate of the isolated kidneys. These effects on MI release were about coincidental with the increase in urinary cyclic 3',5'-AMP after PTH and preceded the peak phosphaturic effect of PTH. There was no detectable effect of PTH on MI synthesis from glucose as a source of the MI released into the urine and perfusate. However, PTH temporarily halted accumulation of tritiated MI catabolites. There was no effect of inactivated PTH on urinary cyclic 3',5'-AMP or on MI transport, which indicates that the PTH effect on MI handling was a specific hormonal effect. These studies clarify the renal metabolism of MI, and they demonstrate heretofore unknown effects of PTH on the renal handling and metabolism of MI. The effects of PTH on renal MI metabolism have important implications in renal carbohydrate metabolism and phospholipid turnover.

Animals↗