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G Rumrich

Publications and source records attributed to G Rumrich.

At least 37 records · Page 2Linked to original sources
PubMed1989

Contraluminal organic anion and cation transport in the proximal renal tubule: V. Interaction with sulfamoyl- and phenoxy diuretics, and with beta-lactam antibiotics.

In order to study the interaction of sulfamoyl- and phenoxy diuretics as well as of beta-lactam antibiotics with the contraluminal anion and cation transport systems the inhibitory potency of these substances against the influx of 3H-para-aminohippurate, 14C-succinate, 35S-sulfate and 3H-N1-methylnicotinamide into cortical tubular cells have been determined. 1.) 2-, 3- and 4-sulfamoylbenzoate inhibit contraluminal PAH influx. N-dipropyl substitution to yield probenecid or ring-substitution to yield furosemide and piretanide augment the inhibitory potency. However, hydrochlorothiazide and acetazolamide exert only a moderate inhibitory potency. Succinate transport was inhibited by furosemide only. Sulfate transport was inhibited by furosemide and 3-sulfamoyl-4-phenoxybenzoate as well as by probenecid, piretanide, hydrochlorothiazide and acetazolamide. 2.) Phenoxyacetate, -propionate, and -butyrate exert increasing inhibition against PAH transport. The weed-killers 2,4-dichloro-, and 2,4,5-trichlorophenoxyacetate (2,4 D and 2,4,5 T) had a similar inhibitory potency, while ethacrynic acid showed a lower and the uricosuric tienilic acid a higher inhibitory potency. None of the compounds of this group interact with contraluminal succinate transport, and only the multiring-substituted compounds 2,4 D, 2,4,5 T, ethacrynic and tienilic acid interact slightly with the sulfate transporter. 3.) The monocarboxylic penicillins benzylpenicillin and phenoxymethylpenicillin as well as the dicarboxylic ticarcillin interact with the contraluminal PAH transport. The aminopenicillin ampicillin had a lower, and apalcillin a higher inhibitory potency than monocarboxylic penicillin. Benzylpenicillin showed small inhibition against succinate transport and ticarcillin against sulfate transport. 4.) The monocarboxylic cephalosporine, 6315 S Shionogi, and the aminocephalosporines, cephalexin and cefadroxil, showed an app. Ki.PAH as the comparable penicillins. The zwitterions cephaloridine and cefpirome did not interact with the PAH transporter, but with the organic cation (NMN) transporter. Amongst the amino-thiazol-containing compounds cefotaxime, ceftriaxone, and cefodizime, increasing interaction with the PAH transporter was seen dependent of a second ionizable anionic group. Compounds with two ionizable anionic groups (cefsulodin, ceftriaxone, cefodizime) exert also a small inhibitory potency against sulfate transport. None of the cephalosporins interacted with the dicarboxylate transporter. The interaction pattern of the tested compounds is in accordance with the specificity requirements for the contraluminal transporters depending on electrical charge and hydrophobicity.

Animals↗
PubMed1988

Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney. IV. Specificity: mono- and polysubstituted benzene analogs.

In order to study the specificities of the contraluminal anion transport systems, the inhibitory potency of substituted benzene analogs on influx of [3H]PAH, [14C]succinate, and [35S]sulfate from the interstitium into cortical tubular cells has been determined in situ: (1) Contraluminal [3H]PAH influx is moderately inhibited by benzene-carboxylate and benzene-sulfonate, and strongly by benzene-dicarboxylates, -disulfonates and carboxy-benzene-sulfonates, if the substituents are located at positions 1 and 3 or 1 and 4. The affinity of the PAH transporter to polysubstituted benzoates increases with increasing hydrophobicity, decreasing electron density at the carboxyl group and decreasing pKa. Similar dependencies are observed for phenols. Benzaldehydes which do not carry an ionic negative charge are accepted by the PAH-transporter, if they possess a second partially charged aldehyde or NO2-group. (2) Contraluminal [14C]succinate influx is inhibited by benzene 1,3- or 1,4-dicarboxylates, -disulfonates and 1,3- or 1,4-carboxybenzene-sulfonates. Monosubstituted benzoates do not interact with the dicarboxylate transporter, but NO2-polysubstituted benzoates do. Phenol itself and 2-substituted phenol interact weakly possibly due to oligomer formation. (3) The contraluminal sulfate transporter interacts only with compounds which show a negative group accumulation such as 3,5-dinitro- or 3,5-dichloro-substituted salicylates. The data are consistent with three separate anion transport systems in the contraluminal membrane: The PAH transporter interacts with hydrophobic molecules carrying one or two negative charges (-COO-, -SO3-) or two or more than two partial negative charges (-OH, -CHO, -SO2NH2, -NO2). The dicarboxylate transporter requires two electronegative ionic charges (-COO-, -SO3-) at 5-9 A distance or one ionic and several partial charges (-Cl, -NO2) at a favourable distance. The sulfate transporter interacts with molecules which have neighbouring electronegative charge accumulation.

Aminohippuric Acids↗
PubMed1988

Contraluminal transport systems in the proximal renal tubule involved in secretion of organic anions.

The transport of organic anions in the proximal tubule occurs primarily through the epithelial cells. This process involves movement across both the luminal and contraluminal membranes via specialized transport systems. Although some of the organic anions are taken up into the cell from the lumen, they can also be accumulated in tubule cells from the interstitial compartment by a variety of transporters. The relative affinities of anions for the different luminal and contraluminal transporters in concert with their conjugate driving forces determine the net directional movement, i.e., organic anion absorption or secretion. By use of the approach of stopped-flow microperfusion, it has been possible to characterize the contraluminal anion transporters in the rat. The following three different systems have been identified: 1) an exchange system for sulfate and oxalate; 2) a cotransport system for Na+ and dicarboxylates; and 3) an exchange system (the so-called p-aminohippuric acid transport system) for hydrophobic anions and long-chain fatty acids. By use of a wide variety of different analogues, the substrate specificities for these different systems were determined. Substrates with two negative ionic charges or with one negative ionic charge and one or more negative partial charges interact with all three systems, depending on the distance between the two charged groups. Polyhalogenated substrates are preferred by the dicarboxylate system. Those substrates which interact only with the p-aminohippurate transport system possess a hydrophobic area and one negative ionic charge or two negative partial charges.

Amino Acids↗
PubMed1987

Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney. II. Specificity: aliphatic dicarboxylic acids.

In order to study the specificity for contraluminal para-aminohippurate (PAH) transport, the inhibitory potency of aliphatic dicarboxylates on 3H-PAH influx, as well as the inhibitory effect on 35SO4(2-)- and 3H-succinate influx, from the interstitium into cortical tubular cells in situ has been determined. The following was found: Testing a homologous series of dicarboxylates--ranging from the 2 C oxalate to the 10 C sebacate--PAH transport was inhibited by succinate (app. Ki 1.35 mmol/l), and all longer dicarboxylates, with high potency (app. Ki 0.05--0.35 mmol/l). Sulfate transport was inhibited only by oxalate (app. Ki 1.1 mmol/l), while dicarboxylate transport was inhibited by succinate, glutarate, adipate and pimelate with decreasing potency (app. Ki 0.04, 0.24, 0.91, 4.0 mmol/l, respectively). PAH transport was inhibited by succinate and glutarate with high potency (app. Ki 1.35 and 0.05 mmol/l), by the correspondent monomethylester to a lesser extent (app. Ki 1.7 and 0.74 mmol/l), but not by the dimethylester. On the other hand, the semialdehyde of succinate with a Ki-value of 1.2 mmol/l, had the same inhibitory potency as succinate itself, while the dialdehyde of glutarate (app. Ki 1.4 mmol/l) was much less potent as glutarate. Introduction of an oxo-, methyl- or sulfhydroxyl-group group onto the 2-position of succinate, or of an oxo-group onto the 2-position of glutarate moderately augmented the inhibitory potency against PAH-uptake. However, introduction of a 2-hydroxy group onto succinate or glutarate in the L-position reduced the inhibitory potency more than in the D-position. Introduction of two methyl-, sulfhydryl- or hydroxyl-groups in the 2-3 position of succinate reduced or abolished its inhibitory potency. The introduction of a 2-amino group onto succinate or glutarate abolished its effect on PAH transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminohippuric Acids↗
PubMed1987

Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney. I. Kinetics, influence of cations, anions, and capillary preperfusion.

In order to study the characteristics of contraluminal para-aminohippurate transport into proximal tubular cells the stopped flow capillary perfusion method was applied. The disappearance of 3H-para-aminohippurate from the capillary perfusate at different concentrations and contact times was measured and saturation type behaviour was found with a Km of 0.08 +/- 0.01 (SE) mmol/l, Jmax of 1.1 +/- 0.1 pmol X s-1 X cm-1 and r, the final extracellular/intracellular distribution ratio of 0.93 +/- 0.03. Omission of Na+ from the capillary test perfusate caused a small reduction of contraluminal PAH uptake at small transport rates (0.1 mmol/l PAH in the test perfusate) but not at high transport rates (1.0 mmol/l PAH in the test perfusate). Change of K+ between 0 and 40 mmol/l and pH between 6.0 and 8.0 did not influence contraluminal PAH uptake. Isotonic replacement of chloride by gluconate, nitrate, sulfate, phosphate, methanesulfonate or increase in bicarbonate to 50 mmol/l did not influence PAH uptake at small transport rates. But isotonic sulfate and phosphate, as well as 50 mmol/l HCO3- and 25 mmol/l Hepes in isotonic solutions reduced PAH uptake at high transport rates. Addition of 5 mmol/l Ca2+, Mg2+, Mn2+, Ba2+, Cd2+ to isotonic Na+-gluconate solution did not influence PAH uptake except for Mg2+ and Mn2+ which inhibited uptake at small transport rates only. Preperfusion of the peritubular capillaries with rat serum, Na+ gluconate (Ca2+- + Mg2+-free), Na+ gluconate (Ca2+- + Mg2+-free) plus 10 mmol/l lactate or pyruvate or 0.1 mmol/l 2-oxoglutarate did not influence PAH uptake at small PAH transport rates, but inhibited at high transport rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminohippuric Acids↗
PubMed1987

Contraluminal para-aminohippurate transport in the proximal tubule of the rat kidney. III. Specificity: monocarboxylic acids.

In order to study the specificity of the contraluminal para-aminohippurate (PAH) transport system, the inhibitory potency of monocarboxylates on the 3H-PAH influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: if a homologous series of fatty acids with increasing chain length is tested, inhibition of contraluminal PAH influx is first seen with valerate (app. Ki 1.4 mmol/l), increasing up to nonanoate (app. Ki 0.06 mmol/l) and remaining in this range up to duodecanoate, the last compound of this series which is sufficiently water-soluble. Similarly, the inhibitory potency of aromatic monocarboxylates increases with increasing hydrophobicity. If the fatty acids are esterified, their inhibitory potency is lost. If they are transformed to the respective aldehydes their inhibitory potency is preserved at a reduced degree. Introduction of a hydrophobic methyl-, ethyl-, or propyl-group increases the inhibitory potency. A beta-, but not an alpha-oxo-group augments the inhibitory potency of phenylpropionate analogs, an OH group diminishes it, and a NH2 group abolishes it. Among phenyl-fatty acids an increase in affinity is observed from phenyl- less than benzoylamine- less than phenoxy- less than benzoyl-acetate and -propionate. All monocarboxylate compounds, so far tested, do not inhibit contraluminal sulfate and Na+/succinate influx. The data indicate that the PAH transporter interacts with monocarboxylates and also with aldehydes which have a hydrophobic moiety. An additional oxo-group facilitates the interaction. Thus, the benzoyl compounds show the highest affinity observed.

Aminohippuric Acids↗
PubMed1985

Contraluminal phosphate transport in the proximal tubule of the rat kidney.

In order to study the characteristics of contraluminal phosphate transport the stopped flow microperfusion technique [13] has been applied. By measuring the time-dependent decrease of interstitial 33Pi concentration at different starting concentrations a simple diffusion kinetics with a permeability coefficient of 7.5 +/- 1.0 X 10(-8) cm2 s-1 was found. Such a kinetic was so far only observed with 2-deoxy-D-glucose. This substance, however, is transported in addition by facilitated diffusion as was seen by paraaminohippurate, methylsuccinate and sulfate. The contraluminal transport of phosphate was inhibited by H2-DIDS (5 mmol/l). It was, however, not influenced by omission of Na+ from the perfusates, by addition of sulfate (150 mmol/l), methylsuccinate (50 mmol/l), arsenate (50 mmol/l), the Hg-compound mersalyl (5 mmol/l), high and low phosphate diet and pH changes between 6.0 and 8.0. The data indicate that phosphate, which is reabsorbed from the lumen by a Na+-dependent transport system, leaves the cell by a rather unspecific contraluminal diffusion pathway.

Animals↗
PubMed1985

Contraluminal sulfate transport in the proximal tubule of the rat kidney. II. Specificity: sulfate-ester, sulfonates and amino sulfonates.

In order to study the specificity for the contraluminal sulfate transport system the inhibitory potency of sulfate esters and sulfonate compounds on the 35SO4(2-) influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: 1. From 10 sulfate monoesters tested 9 inhibited contraluminal sulfate influx with an app. Ki between 0.6 and 6 mmol/l; the two sulfate diesters tested, however, did not. 2. Out of 8 aliphatic sulfonate compounds only three, having a NH- or OH-group in a suitable position, exerted a moderate inhibition (app. Ki ca. 2-6 mmol/l). 3. Amongst 14 benzene sulfonates tested only 2 compounds (5-nitrobenzene-sulfonate and 2-hydroxy-5-nitrobenzenesulfonate) inhibited with a Ki less than 5 mmol/l. 4. Out of 10 naphthalene sulfonates tested 8 inhibited with a Ki less than 5; the highest inhibition was seen with the NH-containing 8-anilinonaphthalene-1-sulfonate (ANS), but no inhibition with 2 compounds containing an amino group. 5. From the polycyclic sulfonates pyrene-3-sulfonate and anthracene-1-sulfonate inhibited with a Ki of approximately 2 mmol/l, while no inhibition was seen with anthracene-2-sulfonate. 6. Out of 4 amino-sulfonates tested benzene-1-amino-sulfonate and a similar benzyl-analog inhibited with a Ki of 1 mmol/l and smaller; cyclohexyl-1-amino-sulfonate (cyclamate), however, inhibited only slightly (app. Ki of 6 mmol/l). The data indicate that sulfate monoesters are well accepted by the contraluminal sulfate transport system. The affinity of sulfonate compounds to this system depends on neighbouring OH-groups --NH-groups, meta-positioned electronegative groups or a hydrophobic moiety in an appropriate position.

Animals↗
PubMed1985

Contraluminal sulfate transport in the proximal tubule of the rat kidney. III. Specificity: disulfonates, di- and tri-carboxylates and sulfocarboxylates.

In order to study the specificity for the contraluminal sulfate transport system the inhibitory potency of disulfonates, di-, tricarboxylates and sulfocarboxylates on the 35SO4(2-) influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: Methane- and ethane-disulfonate as well as benzene-1,3-disulfonate inhibit contraluminal 35SO4(2-) influx (with an (app. Ki of less than 6 mmol/l), while benzene-1,2- and 1,4-disulfonate do not. The inhibitory potency of 1,3-benzene disulfonate is slightly augmented by an additional NH2- or OH-group in position 4. However, OH-groups at position 4 and 5 or 4 and 6 abolish the inhibitory potency. The naphthalene disulfonates tested inhibit only if they have an OH-group in ortho-position to one SO3H group. The stilbene disulfonates H2DIDS and DNDS inhibit the contraluminal 35SO4(2-) influx with high (app. Ki approximately equal to 0.8 mmol/l), DADS with lower potency (app. Ki approximately equal to 6 mmol/l). Amongst the tested aliphatic di- and tricarboxylates inhibition was exerted by oxalate (app. Ki 1.1 mmol/l) and maleate (app. Ki 3.8 mmol/l), but not by malonate, hydroxymalonate and citrate. Out of the tested benzene-dicarboxylates only those inhibit which have the COO- -groups directly on the ring in 1,2 and 1,3 position (app. Ki 4.0 and 2.7 mmol/l), but not in the 1,4 position. An additional OH-group in position 4 augments the inhibitory potency of 1,3 benzene-dicarboxylates (app. Ki 0.8 mmol/l), while an OH group on position 5 abolishes it.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Contraluminal sulfate transport in the proximal tubule of the rat kidney. IV. Specificity: salicylate analogs.

In order to study the specificity of the contraluminal sulfate transport system the inhibitory potency of salicylate analogs (5 mmol/l each) on the 35SO4(2-) influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: 2-hydroxybenzoate (salicylate), per se, did not inhibit contraluminal 35SO4(2-) influx. The same holds when an additional NH2-group was introduced in position 4 or 5, or when an additional Cl-group was introduced in position 4. When an additional Cl- or NO2-group was introduced in position 5 a moderate inhibition was seen (app. Ki approximately equal to 4 mmol/l). However, introduction of 2 Cl- or 2NO2-groups in position 3 and 5 creates compounds with strong inhibitory potency (app. Ki approximately equal to 0.5 mmol/l). 2-hydroxy-3,5-iodobenzoate inhibited too, but with a smaller inhibitory potency (app. Ki approximately equal to 2.3 mmol/l). 2-hydroxybenzoate analogs, which have a carboxy- or sulfo-group in position 5, exerted strong inhibition, those with a acetyl- or butyryl-group exerted moderate inhibition. 1-Naphthol-2-carboxylate did not inhibit, while 1-naphthol-4-sulfamoyl-2-carboxylate did. Amongst the dihydroxybenzoates, 2,3- and 2,5-dihydroxybenzoate did not inhibit contraluminal 35SO4(2-) influx, while 2,4- and 2,6-dihydroxybenzoate did. The data indicate that a hydroxy-group in ortho-position and an electro-negative group in the meta-position to the carboxyl group and paraposition to the hydroxy-group are essential for interaction with the contraluminal sulfate transport system. The ability of 2,6-dihydroxybenzoate to inhibit might be explained by its ability to undergo mesomeric conformation.

Animals↗
PubMed1985

Contraluminal sulfate transport in the proximal tubule of the rat kidney. V. Specificity: phenolphthaleins, sulfonphthaleins, and other sulfo dyes, sulfamoyl-compounds and diphenylamine-2-carboxylates.

In order to evaluate the specificity for the contraluminal sulfate transport system the inhibitory potency of phenol- and sulfonphthaleins, of sulfamoyl-compounds (diuretics) as well as diphenylamine-2-carboxylates (Cl- channel blockers) on the 35SO4(2-) influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: 1) Phenolsulfonphthalein (phenol-red) inhibited with an app. Ki-value of 1.7 mmol/l, while analogs which had additional Br-atoms in position 3 and/or 5, i.e. bromphenol-blue, bromcresol-purple and bromcresol-green, inhibited with an apparent Ki of 0.1 and 0.5 mmol/l respectively. 2) Phenolphthalein and tetrabromphenolphthalein did not inhibit, while the disulfonate dyes bromsulfalein, fuchsin acid and indigocarmine inhibited with a Ki between approximately equal to 1 and 3 mmol/l. The highest inhibitory potency in this class of compounds was seen with orange G (app. Ki 0.07 mmol/l). The monosulfonate dyes tested, fluorescein-sulfonate and orange I inhibited moderately with an app. Ki of approximately equal to mmol/l. 3) The 3-sulfamoyl compounds inhibited to a varying degree, when they had a neighbouring -NH-group (furylmethylamino-group), i.e. in position 6 to the COOH or SO3H-group, or when they had a phenoxy-group in position 4. 4) 4-sulfamoylbenzoate and the related compounds probenecid, acetazolamide and hydrochlorothiazide inhibited with an app. Ki between 4 and 7 mmol/l. 5) All diphenylamine-2-carboxylate analogs inhibited with an app. Ki between 3 and 5 mmol/l, even when the -NH-group was replaced by an = O-group or the benzene ring was replaced by a pyrimidine ring, but not when it was replaced by a thiophen ring.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Secretion and contraluminal uptake of dicarboxylic acids in the proximal convolution of rat kidney.

The transport of dicarboxylic acids in the proximal convolution was investigated by measuring: a) the zero net flux transtubular concentration difference of DL-methyl-succinate, b) its 2-s influx from the interstitium into tubular cells, and c) its 3.5-s efflux from the tubular lumen. With the first method a luminal concentration exceeding the peritubular concentration was observed, thus indicating a net active transtubular secretion of this slowly metabolized substance. All transport steps, luminal and contraluminal , as well as the overall transport, were Na+-dependent and inhibited by lithium (apparent Ki approximately equal to 1.8 mmol/l). The overall transport of methylsuccinate , as well as the contraluminal influx into proximal tubular cells, could be inhibited by paraaminohippurate and H2-DIDS with an apparent Ki of approximately equal to 1.8 mmol/l, by taurocholate with an apparent Ki approximately equal to 3.1 mmol/l and by pyruvate with an apparent Ki approximately equal to 5 mmol/l, but not by sulfate, thiosulfate, L-lactate, oxalate and urate. As judged from the inhibition of contraluminal methylsuccinate influx by 48 dicarboxylic acids (aliphatic and aromatic), a specificity pattern was observed similar to that of inhibition of luminal efflux of 2-oxoglutarate [22]: a preference of dicarboxylates in the transconfiguration with a chain length of 4-5 carbons; little change in the inhibitory potency with CH3-, OH-, SH- and O=, but strong reduction with a NH3+ in the 2 position; only a small reduction of inhibitory potency with 2,3 disubstituted SH and OH analogs; preference of the dicarboxylic benzene in the 1,4 position and of the diacetyl benzene in the 1,2 position. The data indicate a Na+-dependent dicarboxylic transport system at the contraluminal cell side of the proximal tubule which is very similar to the luminal transport system for dicarboxylic acids.

Animals↗
PubMed1984

A stopped flow capillary perfusion method to evaluate contraluminal transport parameters of methylsuccinate from interstitium into renal proximal tubular cells.

In order to study the transport of dicarboxylic acids through the contraluminal cell membrane of proximal tubular cells, 3H- methylsuccinate has been synthetized by catalytic hydration of methylfumarate . As the chromatography of radioactive material excreted in the urine after i.v. injection of 3H- methylsuccinate shows, no metabolite is detectable during the first 3 min. After 10 min, less than 10% of the excreted radiolabel is metabolized. To measure the contraluminal influx of 3H- methylsuccinate from the interstitium into cortical tubular cells, the renal vessels were clamped so that the proximal tubular lumina collapsed. Then Ringer solution was injected into the blood capillaries. It contained different concentrations of 3H- methylsuccinate and 14C-inulin as extracellular space marker. After contact times between 1 and 10 s, this fluid was withdrawn from the capillaries and the disappearance of 3H- methylsuccinate relative to 14C-inulin was measured. The morphological compartments in the outer cortex of the clamped glutaraldehyde-fixed kidney were evaluated by a stereological method. For proximal tubular cells a ratio of extracellular water space to intracellular space of 1:3.1 and a ratio extracellular water space to free cell water space of 1:2 was found. It was tested whether the experimental disappearance curves with 4 different starting concentrations of 3H- methylsuccinate fit with the data from four model calculations. It was found that the data and the conditions of transport are consistent with the predictions of a facilitated diffusion model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Contraluminal sulfate transport in the proximal tubule of the rat kidney. I. Kinetics, effects of K+, Na+, Ca2+, H+, and anions.

In order to study contraluminal sulfate transport the influx rate of 35SO42- from the interstitium into cortical tubular cells has been determined. Preloading of the rat with sulfate augmented contraluminal 35SO42- influx; pre-perfusion with sulfate-free solutions diminished it. The contraluminal 35SO42- influx in sulfate-loaded animals followed two parameter kinetics (Km 1.4 mmol/l, Jmax 1.2 pmol X s-1 X cm-1). The contraluminal 35SO42- influx (starting concentration 10 mumol/l) did not change when the K+ concentration was varied between 4 and 40 mmol/l and the Ca2+ concentration from zero to 3 mmol/l. Omission of Na+ from the perfusates augmented contraluminal 35SO42- influx markedly. The increase is larger at pH 6 than at pH 7.4. Changes of pH affect contraluminal 35SO42- influx only when the solutions are Na+- and K+-free. Under these conditions the 35SO42- influx decreased when the ambient pH was raised from pH 6.0 to pH 8.0. Thiosulfate, selenate, molybdate, oxalate, phosphate, arsenate, and bicarbonate exerted competitive inhibition, while formate, 2-oxoglutarate and paraaminohippurate showed a biphasic response: inhibition at 50 mmol/l, no inhibition at 150 mmol/l. Chloride and bicarbonate inhibited 35SO42- influx at 10 mumol/l 35SO42-, but augmented sulfate influx at 5 mmol/l 35SO42- concentration in rats not preloaded with sulfate. The data indicate the presence of a contraluminal sulfate transport system which is shared by a variety of inorganic and organic anions. The biphasic behaviour of some anions suggests parallel pathways leading to a cis-inhibition at small and trans-stimulation at high anion concentrations. Na+ and H+ may be cotransported or interact with the transport system at a modifier site.

Acid-Base Equilibrium↗
PubMed1983

Reabsorption of dicarboxylic acids from the proximal convolution of rat kidney.

The transport of dicarboxylic acid in the late proximal convolution was investigated by measuring the 3.5 s efflux of 2-oxoglutarate from the tubular lumen of rats starved for 3 days. The 3.5 s efflux of 2-oxoglutarate comprises two components, one due to movement across the brush border, obeying Michaelis Menten kinetics with an apparent Km of 0.13 mmol/l and a Jmax of 0.41 pmol cm-1 s-1 and the other due to diffusional movement presumably via the paracellular pathway with a permeability of 23.0 microns2 s-1. Omission of sodium from the perfusion fluid reduced the transcellular efflux of 2-oxoglutarate by 76%, indicating a sodium-dependent transport system. Addition of 5 mmol/l lithium to the liminal and capillary perfusate reduced it by 56% indicating a specific inhibitory effect of lithium on dicarboxylic acid transport. Addition of 5 mmol/l H2DIDS to the luminal perfusate reduced 3.5 s transcellular 2-oxoglutarate efflux by 35%. The molecular specificity of the system was assessed by studying the inhibitory effects of a series of dicarboxylates, both aliphatic and aromatic, on the 3.5 s efflux of 2-oxoglutarate. Inhibitory constants (apparent Ki) were calculated for comparative purposes assuming competitive inhibition. From this, the system was found to have optimal affinity for dicarboxylates in the trans-configuration with a four or five carbon chain (i.e. succinate and glutarate). Substitution on the 2-carbon atom with CH3-, OH-, SH-, and O = resulted in little reduction in inhibitory potency as compared to succinate itself. However, 2-substitution with NH3+ (not with N-acetyl) as well as 2,3-disubstitution with CH3-, OH- or SH-, strongly reduced or abolished the inhibitory potency. Only with the exception of pyruvate all monocarboxylates tested, did not inhibit 2-oxoglutarate transport, but all tricarboxylates tested, i.e. citrate, isocitrate and tricarballate had an inhibitory effect. Citrate inhibition was higher at acidic than alkaline pH. A number of aromatic compounds was also tested. In most cases the inhibitory potency of the aromatic compounds was considerably weaker than that of the effective 4-5 carbon chain aliphatic compounds. Only benzene-1,4-dicarboxylate, benzene-2-nitro-1,4-dicarboxylate, and benzene-1,2-diacetate had a high inhibitory potency. In the case of the aromatic dicarboxylates the most important feature relating molecular structure to transport was the distance between the two carboxyl-groups in the molecule.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption↗