Less is less: less is not more. Peer review, dollars, NIH and Congress.
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National Institutes of Health (U.S.)↗
Biomedical subjects
D D Fanestil
Publications and source records attributed to D D Fanestil.
Effects of diuretic treatment and of dietary sodium on renal binding of 3H-metolazone.
We report a series of experiments designed to determine if agents and conditions that have been reported to alter sodium reabsorption, Na-K-ATPase activity or cellular structure in the rat distal nephron might also regulate the density or affinity of binding of 3H-metolazone to the putative thiazide receptor in the distal nephron. Experimental conditions selected for study were acute (60-min) and chronic hydrochlorothiazide (HCTZ), acute acetazolamide, acute and chronic furosemide, and 14 days of varied intake of dietary sodium. The density of the binding of 3H-metolazone was increased 47% by acute HCTZ (P less than 0.001) and 39% (P less than 0.001) by acute furosemide. In contrast, acute acetazolamide produced no change in binding despite eliciting a dramatic diuresis. Chronic HCTZ (5 days) and chronic furosemide (7 days) increased binding of 3H-metolazone by 46% (P less than 0.001) and by 101% (P less than 0.001), respectively. Variation of dietary sodium intake over a range that allowed normal growth of the animal and that produced urinary excretion of Na varying from 0.28 to 2.62 mEq/100 g/day failed to alter the density of binding of 3H-metolazone. These studies are the first indication that the density of the thiazide receptor is regulated by a variety of both acute and chronic conditions that have previously been associated with changes in transport, ultrastructure or Na-K-ATPase activity in the distal nephron.(ABSTRACT TRUNCATED AT 250 WORDS)
Acetazolamide↗
Thiazide diuretic receptors in spontaneously hypertensive rats and 2-kidney 1-clip hypertensive rats.
Thiazide diuretic receptor density was assessed in kidneys from spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats by measuring hydroflumethiazide-displaceable 3H-metolazone binding to renal membranes in vitro. Renal thiazide receptor density was not significantly different in 4 week old SHR and WKY rats, but was significantly increased by 20%-40% in 14-49 week old SHRs compared to WKY rats. Affinity of receptors for 3H-metolazone did not differ between SHRs and WKY rats at any age. In WKY rats with 2 kidney-1 clip (2K-1C) hypertension, thiazide receptor density was not significantly different in either clipped or unclipped kidneys from sham-operated controls. Thus, increased renal thiazide receptor density occurs in SHRs along with the development of hypertension and does not appear to be secondary to increased renal perfusion pressure. This increase may reflect altered hormonal or ionic input to the distal tubule and may contribute to elevated sodium reabsorption in this segment in the SHR.
Animals↗
Reversible downregulation of thiazide diuretic receptors by acute renal ischemia.
Receptors for thiazide diuretic drugs in the rat renal cortex have recently been identified through the binding of [3H]metolazone, a potent diuretic with a thiazide-like mechanism of action. The present studies describe the rapid and reversible alterations that occur in thiazide receptors following acute renal ischemia in the rat. The apparent density of thiazide receptors in kidney membranes as measured by the binding of [3H]metolazone was reduced by 90% following 10 min of renal ischemia produced by clamping the renal pedicle. With release of the clamp and subsequent reperfusion for 10 min, thiazide receptor density returned to within 40% of control levels. Ischemia did not alter apparent affinity of receptors for [3H]-metolazone. Sections prepared from renal cortex and incubated in oxygenated media in vitro displayed similar rapid changes in thiazide receptors. Hypoxia of 10- to 30-min duration produced by incubating sections in vitro in nitrogen-saturated media caused a significant decrease in [3H]metolazone binding that was reversible with return to oxygenated media. Similar decreases were obtained in oxygenated sections that were incubated with mitochondrial inhibitors, dinitrophenol and rotenone, but not in sections incubated with ouabain. These results indicate that renal thiazide receptors undergo a rapid and reversible form of regulation and that controlling mechanisms are dependent on metabolic energy.
Acute Disease↗
Photoaffinity labeling of peripheral-type benzodiazepine receptors in rat kidney mitochondria with [3H]PK 14105.
The peripheral-type benzodiazepine receptor in rat kidney has been identified by photoaffinity labeling. PK 14105, a derivative of the selective peripheral-type ligand PK 11195, was used to covalently label peripheral-type benzodiazepine receptors. In the absence of UV light PK 14105 demonstrated reversible, high affinity (KD = 4.8 nM) binding to rat kidney mitochondrial membranes. Inhibition of the reversible binding of [3H]PK 14105 by various benzodiazepine and other ligands demonstrated that this ligand bound with all the characteristics expected of a ligand interacting specifically with peripheral-type benzodiazepine receptors. A similar order of relative potencies was obtained for inhibition of photolabeling, indicating that reversible binding and photolabeling occurred at the same class of binding sites. Examination of photolabeled binding sites from kidney, heart, brain and adrenal membranes using sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the probe is photoincorporated into a single peptide of Mr = 18,500. The results indicate that [3H]PK 14105 identifies the ligand binding domain of the peripheral-type benzodiazepine receptor, which is a peptide with Mr = 18,500, that is of similar size in kidney, heart, brain and adrenals.
Affinity Labels↗
Interactions of lipids with peripheral-type benzodiazepine receptors.
Peripheral-type benzodiazepine receptors (PBRs) are present at high densities in the rat kidney distal tubule. [3H]RO 5-4864 binding to PBRs in kidney membranes is inhibited by several unidentified low molecular weight hydrophobic compounds in urine and serum. We tested representative hydrophobic compounds from several lipid classes for ability to inhibit binding to rat kidney PBRs of two high affinity ligands, [3H]RO 5-4864 and [3H]PK 11195. Unsaturated fatty acids and alcohols inhibited [3H]RO 5-4864 binding with half-maximal inhibition occurring at 3 X 10(-6) M to 10(-4) M. Inhibitory potency increased with the degree of unsaturation. Phospholipids inhibited [3H]RO 5-4864 in the same concentration range, with inhibitory potency in this case dependent both upon an unsaturated fatty acid moiety and upon the polar head group. Phosphatidylethanolamine was the most potent phospholipid tested (IC50 = 2 X 10(-6) M), whereas phosphatidylcholine was not inhibitory. Although phospholipids inhibited both [3H]RO 5-4864 and [3H]PK 11195 binding equally, unsaturated fatty acids had a much greater inhibitory effect upon [3H]RO 5-4864 than upon [3H]PK 11195 binding. Similar effects were obtained with digitonin-solubilized PBRs. These data demonstrate that in our experiments PBR binding was inhibited by specific lipids and that binding of proposed agonist (RO 5-4864) and antagonist (PK 11195) ligands was differentially affected by unsaturated fatty acids.
Animals↗
A monoclonal antibody that recognizes a basolateral membrane protein in A6 epithelial cells.
The A6 cell line is a model for tight epithelia and studies of epithelial polarity. Monoclonal antibodies (MAbs) were produced by immunization of mice with intact A6 cells and fusion of spleen cells to generate hybridomas. Hybridoma supernatants were screened by ELISA to select MAbs binding to the apical membrane of confluent A6 cells. Localization of MAb binding was examined by indirect immunofluorescence using cross sections of A6 monolayers grown on collagen coated filters. One MAb, designated 13F12, was positive by apical surface ELISA but localized specifically to the basolateral membrane of cross sections of A6 monolayers on filters. Immunofluorescence labeling of confluent A6 cells grown on glass cover slips revealed that MAb 13F12 does not bind to the apical membrane, but binds to basolateral determinants in the regions of domes, where it appears able to penetrate cellular junctions. Subconfluent A6 cells express the antigen all over the cell surface. Cells approaching confluency express the antigen on the apical membrane of some cells but not others, and as the cells reach confluency, the antigen disappears from the apical surface, and the cells become fully polarized. A6 cells at confluency on glass cover slips are equally polarized as cells grown on filters with respect to this antigen. The antigen has been identified by immunoprecipitation as a 22 kDa protein. High concentrations of MAb 13F12 did not inhibit cell plating, indicating that the antigenic site is not directly involved in cell adhesion to the substrate. MAb 13F12 should prove to be a useful tool to study many aspects of epithelial polarity, including the signals involved in sorting of proteins to specific membrane domains.
Antibodies, Monoclonal↗
Selective pharmacological modulation of renal peripheral-type benzodiazepine binding by treatment with diuretic drugs.
We have assessed the effects of in vivo administration of different classes of diuretic drugs on the expression of the peripheral-type benzodiazepine binding site (PBBS) in crude membranes derived from the cortex and outer medulla of rat kidney by saturation analysis with the PBBS-selective ligands [3H]RO5-4864 and [3H]PK 11195 in cortex and [3H]RO5-4864 in outer medulla. Administration for 14-15 days of furosemide, a drug that blocks NaCl-KCl coupled transport in the thick ascending limb of the loop of Henle, produced a significant doubling in the PBBS density (Bmax) in outer medulla, a region of the kidney rich in thick ascending limbs, and produced a lesser but significant increase in PBBS density in the cortex. Conversely, administration for 14-15 days of the carbonic anhydrase inhibitor acetazolamide, which acts predominantly in the proximal tubule, and hydrochlorothiazide, which acts predominantly in the early distal tubule, elicited statistically significant increases in PBBS density in renal cortex but not in renal outer medulla. Furthermore, all drug treatments were without effect on the equilibrium dissociation constants (Kds) of [3H]RO5-4864 and [3H]PK 11195 binding to cortical and outer medullary membrane preparations. These findings demonstrate that the PBBS can be selectively "up-regulated" in different regions of the kidney by diuretic drugs with different modes/sites of action.
Acetazolamide↗
Thiazide diuretic drug receptors in rat kidney: identification with [3H]metolazone.
Thiazides and related diuretics inhibit NaCl reabsorption in the distal tubule through an unknown mechanism. We report here that [3H]metolazone, a diuretic with a thiazide-like mechanism of action, labels a site in rat kidney membranes that has characteristics of the thiazide-sensitive ion transporter. [3H]Metolazone bound with high affinity (Kd = 4.27 nM) to a site with a density of 0.717 pmol/mg of protein in kidney membranes. The binding site was localized to the renal cortex, with little or no binding in other kidney regions and 11 other tissues. The affinities of thiazide-type diuretics for this binding site were significantly correlated with their clinical potency. Halide anions (Cl-, Br-, and I-) specifically inhibited high-affinity binding of [3H]metolazone to this site. [3H]Metolazone also bound with lower affinity (Kd = 289 nM) to sites present in kidney as well as in liver, testis, lung, brain, heart, and other tissues. Calcium antagonists and certain smooth muscle relaxants had Ki values of 0.6-10 microM for these low-affinity sites, which were not inhibited by most of the thiazide diuretics tested. Properties of the high-affinity [3H]metolazone binding site are consistent with its identity as the receptor for thiazide-type diuretics.
Animals↗
Binding of calcium to the proteolipid phosphorin.
Phosphorin is a phosphate-binding proteolipid isolated from rabbit kidney brush border membrane vesicles that binds inorganic phosphate with high affinity and specificity. This binding of phosphate has a Hill coefficient of 1.92 and an absolute requirement for the presence of a divalent metal. We now describe the binding of Ca2+ to phosphorin that had been depleted of endogenous divalent metal. The dependence of the binding of Ca2+ over the concentration range of 5-100 microM produced a sigmoidal curve, yielding a Hill coefficient of 2.46. (Ruthenium red and La3+ were also potent inhibitors of Ca2+ binding). The divalent metals Mn2+ and Mg2+ were able to inhibit binding of Ca2+ and produced Hill coefficients of 1.75 and 1.98; however, Ba2+ and Sr2+ were less effective in their ability to inhibit binding. In addition, the amine-reactive reagent, 4,4'-diisothiocyano-2,2'-disulfonic acid (DIDS), which had previously been found to inhibit binding of phosphate to phosphorin, also completely inhibited binding of Ca2+. We propose that a phosphorin-Me2+ complex forms the molecular species that binds phosphate.
4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
Mechanism of action of aldosterone blockers.
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Aldosterone↗
Modification of the peripheral-type benzodiazepine receptor by arachidonate, diethylpyrocarbonate and thiol reagents.
Peripheral type benzodiazepine receptors are differentially modified by arachidonate, diethylpyrocarbonate and thiol reagents, as evidenced by the finding that binding of a proposed agonist ([3H]R05-4864) and a proposed antagonist ([3H]PK 11195) to rat kidney mitochondrial membranes can be modified separately. (1) Arachidonate significantly lowered the affinity of the peripheral-type benzodiazepine receptor for R05-4864 and diazepam but did not alter the affinity for PK 11195 and only slightly altered for dipyridamole. In contrast, diethylpyrocarbonate inhibited [3H]PK 11195 binding by 43% while reducing [3H]R05-4864 binding only 16%. (2) Diethylpyrocarbonate treatment causes a reduction in affinity for both dipyridamole and PK 11195, did not change the affinities for R05-4864 and diazepam but increased the affinities for diuretics. PK 11195, R05-4864 and dipyridamole totally protected peripheral benzodiazepine receptors against inactivation by diethylpyrocarbonate. In contrast, diethylpyrocarbonate inactivation of [3H]PK 11195 binding was increased after preincubation of peripheral benzodiazepine receptors with metolazone. Arachidonate both lowers the affinity for [3H]R05-4864 and eliminated the ability of R05-4864 to protect peripheral benzodiazepine receptors against inactivation by diethylpyrocarbonate. (3) Among different thiol reagents, only dithiothreitol treatment resulted in 26 and 43% inhibition of [3H]PK 11195 and [3H]R05-4864 binding, respectively. These results indicate that the peripheral-type benzodiazepine receptor molecule possesses at least two different conformations or separate mutually exclusive sites for agonists and antagonists. Additionally, the interaction of the thiazide class of diuretics with peripheral-type benzodiazepine receptors seems to require binding sites on the receptor molecule in addition to those for specific agonist and antagonist, whereas dipyridamole appears to bind to the antagonist site or conformation.
Animals↗
Effect of adrenocorticoid receptors on potassium and sodium flux in rat C6 glioma cells.
C6 glioma cells contain two types of receptors for adrenocorticoids. Glucocorticoid (Type II) receptors are present at higher density and mediate increases in glycerol phosphate dehydrogenase and glutamine synthetase activity. The function of mineralocorticoid (Type I) receptors present at low density in C6 cells is unknown. Since mineralocorticoid (Type I) receptors in renal epithelial cells regulate cation transport, we sought to determine whether adrenocorticoid receptors located in glioma cells are similarly linked to electrolyte transporting activity. Occupation of mineralocorticoid receptors in C6 glioma by adrenocorticoids did not alter Na+ or K+ transport, in contrast to their effects on renal epithelial and vascular smooth muscle cells. Occupation of glucocorticoid receptors produced a 20-25% decrease in K+ uptake into C6 cells, but did not alter Na+ influx. Stimulation of Na+ influx with the ionophore monensin produced a large ouabain-sensitive increase in glucose utilization, as measured by 2-deoxyglucose uptake. However, mineralocorticoid receptor occupation did not alter glucose utilization, providing further evidence that these receptors do not influence Na+ transport in C6 cells. These studies provide evidence that mineralocorticoid receptors in glioma cells do not regulate Na+ or K+ transport. Glial glucocorticoid receptors have an inhibitory effect on glial K+ influx, which may contribute to glucocorticoid hormone effects on brain excitability.
Animals↗
Heterogeneity of expression of apical membrane determinants in A6 epithelial cells.
Expression of apical membrane antigens by A6 cells is heterogeneous. The A6 cell line is a model system for sodium transport and hormone action in "tight" epithelia. To create probes for the study of sodium transport and aldosterone action, we generated monoclonal antibodies (MoAbs) by immunization of BALB/c mice with intact A6 cells. MoAbs binding to apical membrane determinants were selected by an enzyme-linked immunoadsorbance assay (ELISA) against the apical surface of confluent A6 monolayers. Examination of ELISA-positive MoAbs by indirect immunofluorescence on confluent cells grown on glass cover slips revealed heterogeneity of apical expression: individual cells comprising the monolayer were fluorescently labeled to variable degrees and some cells were unlabeled. Expression of one antigen, recognized by MoAb I4C1, was heterogeneous in cells at low density as well as for confluent cells. Another antibody, 2B8, exhibited heterogeneity of labeling in confluent A6 monolayers, but no labeling of any cells at low density. This heterogeneity of antigen expression suggested that A6 cells are not a single cell type. However, cloned A6 cells established by limiting dilution were also labeled heterogeneously by both antibodies. Thus the heterogeneity observed is not due to genetic inhomogeneity between cells. Expression of the antigens on apical membranes of cells grown on Millipore filters was heterogeneous for the antigen recognized by 2B8, but essentially homogeneous for that recognized by I4C1, suggesting that the degree of differentiation of the cells plays a role in the heterogeneous expression of apical antigens. This heterogeneity of expression of apical antigens adds new complexity to the study of A6 cells and the differentiation of epithelial cells in culture.
Animals↗
Interactions of diuretics with the peripheral-type benzodiazepine receptor in rat kidney.
The peripheral-type benzodiazepine receptor (PBR) has been autoradiographically localized to the thick ascending limb and early distal tubule. To elucidate further the role of this receptor in kidney function, we have examined the effects of all classes of diuretics on the binding of labeled PBR-specific ligands (R05-4864, PK 11195) to rat kidney membranes (13,000 X g X 10 min). Drugs capable of inhibiting R05-4864 binding by 50% at less than 200 microM included: metolazone (IC50 = 1 microM), indacrinone (IC50 = 42 microM), indapamide (IC50 = 58 microM), hydrochlorothiazide (HCTZ; IC50 = 117 microM) and trichloromethiazide (IC50 = 175 microM). Conversely, diuretics of the loop (e.g., furosemide), K+-sparing (e.g., triamterene), and carbonic anhydrase inhibitor (e.g., acetazolamide) classes exerted no significant effects on R05-4864 binding (IC50S greater than or equal to 1 mM). Inhibition by indacrinone was stereoselective. Thiazide-like compounds inhibited R05-4864 binding with a rank-order of potencies similar to that for their enhancement of in vivo natriuresis (metolazone greater than HCTZ approximately equal to trichlormethiazide greater than chlorothiazide). Scatchard analysis revealed that metolazone, indacrinone, indapamide and HCTZ inhibited R05-4864 binding by reducing Kd, with no effect on maximum binding. The apparent Kd of metolazone for the renal PBR was 3.8 X 10(-7) M. IC50 values of 14 metolazone derivatives for inhibition of R05-4864 binding correlated well (r = .71, P less than .01) with their natriuretic efficacies. PK 11195 binding to digitonin (1.2 mg/mg of protein)-solubilized membranes displayed the same rank-order of, but was twice as sensitive to inhibition by metolazone, indacrinone, indapamide and HCTZ.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Interference by lipids in the determination of protein using bicinchoninic acid.
Bicinchoninic acid forms the basis of an analytical method for the determination of protein. The reagent produces a purple complex with cuprous ion (Cu+) in an alkaline environment and is the basis for the monitoring of cuprous ions produced in the reactions of proteins with alkaline Cu2+. This method of protein determination was reported to have greater tolerance to many commonly encountered interfering compounds, when compared to the Lowry technique. However, we have found the bicinchoninic acid technique to produce erroneously high values for protein when common membrane phospholipids were included in the assay. Phospholipids in the presence of bicinchoninic acid produced an absorbance peak similar to that produced by protein. This absorbance was linear with concentration, however, the slope varied for individual phospholipids. The combined absorption of phospholipid and protein was not strictly additive. The results indicate that the presence of appreciable quantities of lipid in samples can cause significant error in the analysis of protein by the bicinchoninic acid procedure.
Copper↗
Reconstitution of the partially purified renal phosphate (Pi) transporter.
Proteins from rabbit kidney brush border membranes were solubilized with 1% Nonidet P-40 (crude membrane proteins) and fractionated according to their isoelectric points (pI) by chromatofocusing. The eluate was pooled into three fractions according to the pI of the samples (1, greater than 6.8; 2, 6.8-5.4; 3, 5.4-4.0). The crude membrane proteins as well as the three fractions were reconstituted into liposomes and transport of Pi was measured by a rapid filtration technique in the presence of an inwardly directed K+ or Na+ gradient. Arsenate-inhibitable Na+-dependent transport of Pi was reconstituted into an osmotically active intravesicular space from both the crude membrane proteins and Fraction 1. In contrast, Fractions 2 and 3 were inactive. Treatment of the crude membrane proteins and the three fractions with the method for extracting phosphorin (a Pi-binding proteolipid found in brush border membranes) yielded Mn2+-dependent binding of Pi characteristic of phosphorin only in the extracts from crude membrane proteins and Fraction 1, the same fractions in which Na+-dependent transport of Pi was found in the reconstituted system. When reconstituted into liposomes, phosphorin was, however, unable to yield Na+-dependent transport of Pi. Moreover, we cannot eliminate the possibility that Na+-Pi transport can occur in the absence of phosphorin, since complete recovery of Na+-Pi transport was not achieved. However, the present data showing localization of the recovered binding and transport systems for Pi in the same protein fraction lend support to the hypothesis that phosphorin might be a constituent of the renal Pi transport system. Whether the presence of phosphorin is necessary or accessory for Na+-dependent Pi transport in intact brush border membrane vesicles or in liposomes reconstituted with crude or purified membrane proteins requires further investigation.
Animals↗
Phosphorin, a phosphate-binding hydrophobic protein isolated from renal brush border membranes.
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Biological Transport↗