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J B Pritchard

Publications and source records attributed to J B Pritchard.

14 recordsLinked to original sources
PubMed1992

Functional expression of renal organic anion transport in Xenopus laevis oocytes.

Secretion of organic anions by the kidney plays a critical role in the elimination of toxic agents from the body. Recent findings in isolated membranes and intact tissue have demonstrated the participation of multiple transport proteins in this process. As a first step toward molecular characterization of these proteins through expression cloning, the studies reported below demonstrate functional expression of both fumarate- and lithium-sensitive glutarate and probenecid-sensitive p-aminohippurate transport in Xenopus oocytes injected with rat kidney poly(A)+ RNA. Maximal increase in substrate uptake over buffer-injected controls was reached by 5 days after mRNA injection. Expression of size-fractionated mRNA indicated that the active species with respect to both transport activities were in the range of 1.8 to 3.5 kb.

Animals↗
PubMed1991

Comparative insights into the mechanisms of renal organic anion and cation secretion.

Comparative models have played a major role in defining the mechanisms that enable vertebrate proximal tubules to transport organic anions and cations from the peritubular interstitium to the urine. The unique advantages of these models and their contributions to our understanding of organic anion and cation transport mechanisms are summarized here. Recent studies of the organic anion transport system suggest that transport is coupled to metabolic energy via indirect coupling to the sodium gradient. Organic anions enter the cell across the basolateral membrane in exchange for alpha-ketoglutarate (alpha-KG), and the alpha-KG is returned to the interior via Na-alpha-KG cotransport. Indirect coupling to Na has been demonstrated in both isolated membranes and intact renal epithelial cells of species ranging from marine crustaceans to mammals. This mechanism was shown to drive not only cellular accumulation but also secretory transepithelial fluxes of organic anions. Luminal exit of secreted organic anions appears to be carrier mediated but is, at present, poorly understood, with mediated potential-driven efflux and anion exchange-driven efflux implicated in some species. As for organic anions, the renal clearance of some organic cations approaches the renal plasma flow. Although there is considerable variation in the handling of specific substrates between species, the basic properties of organic cation transport include carrier-mediated potential-driven uptake at the basolateral membrane, intracellular sequestration that reduces the free concentration of the cation, and luminal exit by organic cation-proton exchange. Reabsorptive transport is also observed for some organic cations, but its mechanisms and driving forces are not well understood.

Animals↗
PubMed1991

Indirect coupling of organic anion secretion to sodium in teleost (Paralichthys lethostigma) renal tubules.

Recent findings in both rat and crab indicate that renal accumulation of p-aminohippurate (PAH) across the basolateral membrane can be coupled indirectly to the Na gradient through PAH-glutarate exchange and Na/glutarate cotransport. However, the role of this mechanism in net transepithelial PAH secretion was not examined. Therefore, proximal tubules from Southern flounder kidney were used to assess both the presence of indirect coupling in the fish and its relationship to net secretion. [14C]glutarate uptake by proximal tubular masses was concentrative, Na dependent, and Li inhibitable. Glutarate efflux from preloaded masses was stimulated by addition of PAH to the medium. Thus flounder tubules exhibited both Na/glutarate uptake and glutarate-PAH exchange. Furthermore, steady-state [3H]PAH accumulation was increased 50% by 10-50 microM glutarate, and this increase was abolished by Li, indicating indirect coupling of PAH entry to Na. To determine whether indirect coupling affected net secretion as well as tissue accumulation, the steady-state accumulation of an anionic dye, fluorescein (FL), was measured in individual renal tubules by use of epifluorescence microscopy and video-image analysis. FL accumulated in tubules to levels that were 20-40 times higher than the medium. In most fish, luminal fluorescence was measurably higher than cellular, and uptake in both compartments was markedly reduced by PAH and Li. Moreover, FL accumulation in cells and lumina was increased by 70-100% when 50 microM glutarate was added to the bathing medium. Thus glutarate not only stimulated uphill FL entry into the cells, but also stimulated active secretion into the tubular lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Toxic substances and cell membrane function.

The exposed location and functional importance of cell membranes make them particularly susceptible to the toxic effects of many chemicals. The likelihood of such effects has been appreciated for many years. However, the recent advent of new techniques has greatly increased our understanding of the complexities of membrane structure and function. These data make it quite clear that the interaction of toxic compounds with either the protein or the lipid component of cell membranes may substantially alter membrane function. This paper summarizes the current concepts of membrane structure and function and discusses the techniques currently in use to study cell membranes. Several examples are presented in which xenobiotics significantly alter membrane function. These include effects of heavy metals on passive ion permeability, impairment of osmoregulation and calcium transport by organochlorine pesticides, inhibition of the transport of neurotransmitter metabolites by phenoxyacetic acid herbicides in choroid plexus, and reduction in intestinal nutrient transport by heavy metals. Hence the study of the interactions of foreign compounds with membrane function may enhance our understanding of mechanisms both of toxicity and of basic membrane function.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1979

Determinants of the renal handling of 2, 4-dichlorophenoxyacetic acid by winter flounder.

The factors determining the renal handling of 2,4-dichlorophenoxyacetic acid (2,4-D) were examined in winter flounder, Pseudopleuronectes americanus, using isolated tubules and clearance techniques. In vitro, extensive energy-dependent uptake was seen with tissue/medium ratios of 30-fold at 1 micronM 2,4-D. The velocity of uptake was concentration-dependent with apparent Km and Vmax v,lues of 70 micronM and 3.6 micronmol/g of tubules per hr, respectively. Uptake was inhibited by other organic acids and 2,4-D competitively inhibited p-aminohippurate uptake. 2,4-D did not inhibit organic cation transport by the tubules. In vivo, 2,4-D was actively secreted with clearances of nearly 500 times the glomerular filtration rate at 1 micronM 2,4-D in plasma. At higher plasma concentrations (10-60 micronM) a transport maximum of 0.85 micronmol/g of kidney per hr was observed. Secretion was inhibited by other organic acids. 2,4-D also inhibited p-aminohippurate secretion in vivo. Little metabolism was noted; approximately 10% was excreted as the taurine conjugate. Plasma binding was 70%. Examination of the effects of added proteins on in vitro uptake showed that protein binding could limit 2,4-D transport but that flounder plasma (low in albumin) was far less effective than bovine serum albumin in binding and inhibition of transport. The roles of plasma binding, intracellular binding and metabolism in determining the rate of 2,4-D elimination by the kidney are discussed.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1978

Renal sugar transport in the winter flounder: V. secretion of 2-deoxy-D-galactose.

Isolated renal tubules and renal clearance techniques were used to characterize the renal handling of 2-deoxy-D-galactose (2-d-Gal) by the winter flounder (Pseudopleuronectes americanus). In vitro, energy-dependent, pH-sensitive uptake of 2-d-Gal (2-100 micron) was seen at the antiluminal face of the cell. Clearance measurements showed net secretion of 2-d-Gal in vivo. The mean clearance of 2-d-Gal in 18 fish was 0.98 +/- 0.16 ml/h while the glomerular filtration rate (GFR) was only 0.37 +/- 0.10 ml/h. Secretion was associated with marked renal accumulation of both 2-d-Gal and phosphorylated derivatives (2-d-Gal-1-phosphate). Tissue-to-plasma ratios (T/P) averaged 19 for free sugar and 59 for total sugar. Both clearance ratio and T/P were reduced to approximately 1 by injection of galactose (2.5 mmol/kg) simultaneously with 2-d-Gal (25 mumol/kg). Phlorizin (2.5 mumol/kg) increased net 2-d-Gal secretion, whereas glucose (2.5 mmol/kg) produced no change in secretion. Both compounds depressed 2-d-Gal T/P. This result suggests the presence of readsorptive transport at the brush border, sensitive to glucose and phlorizin.

Anaerobiosis↗
PubMed1978

Kinetic analysis of the renal handling of 2,2-bis(p-chlorophenyl) acetic acid by the rat.

The kinetics of uptake and efflux of organic acids in rat renal cortical slices were used to examine the affinity of 2,2-bis(p-chlorophenyl)acetic acid (DDA) for the organic acid transport system and to assess intracellular binding of this polar 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) metabolite. As judged by its ability to inhibit p-aminohippuric acid transport, DDA was a potent competitive inhibitor, almost as strong as probenecid, the classical inhibitor of this system. Efflux of DDA from slices demonstrated that the bulk (85%) of the DDA within the slice was reversibly bound to proteins or other macromolecules. Cortical slices incubated 60 minutes with 10 micron DDA contained a total concentration of 160 micron DDA within the tubular cells, but the actual free concentration in the cells was only 20 to 30 micron. Thus, although DDA was accumulated against a concentration gradient by the kidney, the gradient was much smaller than the measured tissue/medium ratio. Potential consequences of DDA exposure through its interaction with the organic acid system and roles of DDA binding sites in the toxicity and transport of DDA are discussed.

Animals↗
PubMed1977

Renal handling of the polar DDT metabolite DDA (2,2-bis[p-chlorophenyl] acetic acid) by marine fish.

The renal handling of 2,2-bis(p-chlorophenyl) acetic acid (DDA) was examined in the isolated tubules of the winter flounder (Pseudopleuronectes americanus) in vitro in conjunction with clearance studies in the flounder and in the aglomerular goosefish (Lophius americanus). In vitro, both uptake studies and autoradiography showed extensive energy-dependent accumulation within the cytoplasm of tubular cells and the tubular lumen. The uptake was strongly inhibited by p-aminohippurate and chlorophenol red. A second component of uptake was insensitive to metabolic inhibitors or organic acids and represented tissue binding. In vivo, both species showed net secretion which was inhibited by probenecid. Comparison of DDT and DDA distribution and excretion emphasized the importance of the greater water solubility of DDA and of its secretory transport, since DDA was excreted at over 200 times the rate of DDT. Liver, kidney, and bile also showed elevated DDA tissue-to-plasma ratios. Thus, the organic acid system mediates the accumulation and excretion of DDA in these fish.

Animals↗
PubMed1976

Tissue distribution of (14C) methyl mercury in the lobster, Homarus americanus.

[14C] Methyl mercury was administered by three different routes: intravascular (iv) injection, ingestion, and absorption from the ambient water. After iv administration (0.1 mg/kg) [14C] methyl mercury was rapidly removed from the plasma, followed by slow loss from the hepatopancreas and a strikingly persistent increase in the amount of radioactivity in the tail muscle. Most (80-90%) of the radioactivity in the hepatopancreas was shown by TLC methods to be the parent compound, and approximately 10% of this persisted for 6 days after injection. The half-life in this organ was found to be 21 days. One month after iv treatment with methyl mercury, the only organs that contained more than 0.1 ppm of this xenobiotic were egg masses, male gonads, heart, brain, intestine, and tail muscle. The half-lives for disappearance from sexual organs were greater than 1 month. After ingestion of [14C] methyl mercury (0.1 mg/kg) in food the hepatopancreas contained most of the administered dose at 6 days (68%), while the stomach (10%), tail muscle (8%), and carcass (15%) contained less. A unique distribution pattern emerged 6 days after exposure to [14C] methyl mercury-containing ambient water (0.1 ppm). The tail muscle contained most (50%) of the absorbed dose, whereas the hepatopancreas and carcass contained only 23 and 10%, respectively. In view of the small molecular size and high lipid solubility of methyl mercury and the lipophilic properties of the chitin-protein exoskeleton of the lobster, it is likely that significant uptake directly from the water as well as storage of absorbed methyl mercury occurred in the tail region. Residue analysis on untreated lobsters indicated that the egg masses contained the largest amount of methyl mercury (0.1 ppm). The hepatopancreas and carcass (muscle) levels were less than 0.05 ppm.

Absorption↗
PubMed1976

Renal sugar transport in the winter flounder. I. Renal clearance studies.

The renal handling of several sugars was examined using clearance techniques in the winter flounder Pseudopleuronectes americanus. The nonmetabolizable sugar alpha-methyl-D-glucoside was extensively reabsorbed, with consequent accumulation in renal tissue to nearly twice plasma concentration. Both glucose and phlorizin abolished reabsorption and reduced tissue-to-plasma ratios (T/P). D-Galactose was reabsorbed. However, the T/P for free galactose was only 0.6 (total sugar was 1.7). Glucose and phlorizin produced only a transient decrease in reabsorption and no change in T/P. 2-Deoxy-D-glucose showed neither net reabsorption nore secretion. Nevertheless, kidney T/P were inexcess of 6 for total sugar and 1.2 for free sugar, indicating entry through the peritubular face of the tubule. Neither glucose nor phlorizin altered 2-deoxy-D-glucose clearance, but both reduced T/P for total sugar (2.4) and free sugar (0.7). Thus, several systems govern the handling of these sugars at the luminal membrane of the renal tubule, just as has been previously demonstrated at the peritubular membrane in this species.

Animals↗
PubMed1975

Uptake and supply of purine compounds by the liver.

We have analyzed for purine compounds entering and leaving the liver in lightly anesthetized rabbits and rats and for the export of utilizable purine from liver perfused with oxypurine. The in vivo results indicate that roughly 80% of hypoxanthine, xanthine, and urate is removed in a single passage of blood through liver. Conversely, the adenosine concentration of hepatic venous blood is increased 10-fold over portal or arterial levels. When the liver is isolated and perfused with hypoxanthine there is significant release of adenosine, whether measured quantitatively by microbiological assay or qualitatively by analysis of the radioactive purines released from liver that has been prelabeled with [14C]hypoxanthine. These results provide direct evidence for the clearance of hydroxylated purines and the release of utilizable adenine derivatives by liver.

Adenosine↗
PubMedDate not supplied

Platinate toxicity: past, present, and prospects.

Using traditional toxicologic methods, four species were studied for their qualitative and quantitative predictiveness of the toxic effects of cis-dichlorodiammineplatinum(II) in man. Of the four species studied, mouse, monkey, rat, and dog, the latter two gave the best overall results. Using an in vivo rat model, it was found that except for chloroplatinic acid, eight of the tested analogs were less nephrotoxic than the parent drug, cis-dichlorodiammineplatinum(II). The in vitro renal toxicity screen using flounder tubules showed that of the 26 compounds studied, about half were less toxic than the parent compound. This in vitro mini-tox system can be performed about 30 times faster and at one fiftieth the cost of the in vivo model. The in vitro studies also provided evidence that the biochemical site of toxicity of platihates is on ATPases. The latter studies suggested a basis for unifying the mechanistic interpretation of the toxic actions on such disparate target organs as the kidney, nerve, stomach, and inner ear.

Adenosine Triphosphatases↗