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D G Warnock

Publications and source records attributed to D G Warnock.

At least 19 recordsLinked to original sources
PubMed1992

Cloning, sequencing, and expression of Na(+)-H+ antiporter cDNAs from human tissues.

Two types of Na(+)-H+ antiporter with different sensitivities to amiloride analogues have been identified in mammalian plasma membranes. A human Na(+)-H+ antiporter cDNA was obtained by Sardet and co-workers (C. Sardet, L. Counillon, A. Franchi, and J. Pouysségur. Cell 56: 271-280, 1989) using mutant mouse fibroblasts lacking Na(+)-H+ antiporter transformed with human genomic DNA. However, the amiloride sensitivity of this cloned Na(+)-H+ antiporter was not precisely determined. Furthermore, the reported cDNA sequence may be a chimera of human and mouse genes. Hence we isolated a Na(+)-H+ antiporter cDNA actually expressed in human tissues and characterized its amiloride sensitivity. Our 4 kb cDNA obtained from human kidney cortex contained the identical open reading frame to that previously reported and the entire 3' terminus, which was quite different from that reported. This discrepancy was not due to differences in tissue-specific expression because cDNAs from different human tissues were identical, and single bands were observed under high stringency on Northern blots of various human tissues. Na(+)-H+ antiporter activity of mutant mouse fibroblasts deficient in Na(+)-H+ antiporter activity transfected with the cloned cDNA was very sensitive to amiloride and 5-N substituted analogues of amiloride. Thus the cloned cDNA represents the NHE-1 isoform of the Na(+)-H+ antiporter.

Amiloride↗
PubMed1991

IgA nephropathy in blacks: studies of IgA2 allotypes and clinical course.

The prevalence of IgA nephropathy (IgAN) varies among racial groups, being most common among Caucasians and Orientals and rare in Blacks. Other investigators have hypothesized that the risk for IgAN may be influenced by the IgA2 allotype. It has been suggested that the rare Black patients with IgAN may be homozygous for the A2m(1) allele which predominates in Whites, but is less common in Blacks. In a multicenter study, 27 Black IgAN patients were enrolled to investigate this hypothesis and analyze the clinical course of disease in Blacks. The IgA2 allotypes of 18 Black patients and 14 controls were determined using restriction fragment length polymorphism analysis. Three patients were homozygous for the A2m(1) allele, four were homozygous for A2m(2) and 11 were heterozygous. The respective allelic frequencies of A2m(1) and A2m(2) were 0.47 and 0.53 and did not differ significantly from Black controls. Most clinical manifestations of disease did not significantly differ with respect to distribution of the two alleles, although the gender ratio differed between the homozygous A2m(1) and heterozygous patients. The presence of the A2m(1) allele did not increase the risk for IgAN, and the presence of the A2m(2) allele or homozygosity for this allele did not protect Blacks from the development of IgAN.

Adult↗
PubMed1989

Pharmacokinetics of esmolol and ASL-8123 in renal failure.

The effect of renal function on the pharmacokinetics of esmolol, an ultra-short-acting beta-adrenergic blocker, and its major metabolite, ASL-8123, was examined in six healthy control subjects, six patients maintained on hemodialysis, and six patients on continuous ambulatory peritoneal dialysis (CAPD). In addition, the impact of hemodialysis and CAPD on removal of esmolol and ASL-8123 was determined. Multiple blood, urine, and dialysate samples were collected during a 72-hour period and assayed for esmolol and ASL-8123 by HPLC. The pharmacokinetic disposition of esmolol was not significantly altered by renal failure. Mean (+/- SD) total body clearance for esmolol was 171.4 +/- 69.8, 249.8 +/- 176.3, and 265.3 +/- 143.1 ml/min/kg for the control, hemodialysis, and CAPD patients, respectively. Mean elimination half-life (t1/2) was 7.2 minutes in control subjects compared with 7.1 and 8.0 minutes for the hemodialysis and CAPD groups, respectively. The apparent volume of distribution of esmolol did not differ significantly among the three groups. ASL-8123 was shown to accumulate in patients with renal failure, as evidenced by a mean maximum blood concentration of 42.8 +/- 12.2 micrograms/ml in the control group compared with 76.1 +/- 23.9 and 87.1 +/- 20.4 micrograms/ml in the hemodialysis and CAPD groups, respectively (p less than 0.05). The elimination t1/2 of ASL-8123 was prolonged in patients with renal failure, averaging more than 42 hours compared with only 4 hours in the control subjects. Approximately 20% of the esmolol dose as ASL-8123, was removed by either hemodialysis or CAPD, contributing minimally to the elimination of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1989

K-Cl cotransport systems.

The KCl cotransporter in the basolateral membrane of renal tubules may play a central role in the transcellular transport of NaCl. Because this transporter is electrically neutral, and also functions in parallel to the electrogenic Na,K-ATPase, there is an imbalance in charge which must be expressed as a cationic current across the basolateral membrane. Therefore, other pathways must also function in the basolateral membrane which permit the conductive exit of K+ in addition to the electrically-neutral KCl cotransporter. Another functional role for the KCl cotransporter is manifest during the cell volume regulatory response to cell swelling. In this setting (regulatory volume decrease), it appears that both electrically-neutral and electrically-coupled KCl efflux pathways are acutely activated. Very little is known at present about the mechanisms of short and long term regulation of the KCl cotransporter. A major obstacle at this point is the lack of a suitable, potent (that is, microM range) specific inhibitor of this transporter. It also appears that the chloride transport systems in basolateral membrane vesicles may be greatly influenced by the precise details of the method of preparation. Once these experimental details are mastered, and a suitable high affinity inhibitor is identified, then the detailed characterization and identification of the KCl cotransporter can be undertaken.

Animals↗
PubMed1989

Distinct epitopes on amiloride.

Most Na(+)-selective transport proteins are inhibited by the drug amiloride. Studies using amiloride analogues suggest that specific regions of amiloride might participate in binding to receptors on these transport proteins. To determine whether certain domains of this drug are recognized as distinct epitopes, amiloride was coupled to albumin through either its C-5 NH2-group on the pyrazine ring or through a terminal NH2-group of the guanidino moiety, and antibodies were raised against these amiloride-albumin conjugates. Studies of antibody binding to amiloride analogues identified the 3,5-diaminopyrazinyl, the guanidinocarbonyl, and the C-6 halo moieties as distinct epitopes, although the antibodies required the presence of both the 3,5-diaminopyrazinyl as well as the guanidinocarbonyl moiety for binding.

Amiloride↗
PubMed1989

Accumulation of weak base in gastric mucosa provides evidence for an acidic storage compartment.

Uptake and release of acridine orange (AO), a fluorescent weak base that accumulates in acidic spaces, were studied in perfused frog gastric mucosa. Tissue was mounted between two flow-through chambers and loaded with AO on the mucosal side. AO washout and acid secretion rate were monitored simultaneously by a flow-through fluorescence detector and a pH-stat, respectively. Data were displayed on a computer screen, stored, and analyzed. AO, in concentrations as high as 0.02 mM, does not affect the acid secretion rate. Nonlinear least-squares analysis of AO washout curves resolved two exponential components: a faster component associated mainly with AO washout from the chamber and a slower component reflecting primarily AO washout from the tissue. The slower exponential declines more slowly at higher concentrations and/or longer duration of AO loading, whereas the faster exponential is unaffected. AO washout is unaffected by the level of the steady-state acid secretion rate. Nitrite inhibits the acid secretion rate but does not affect the AO washout. When nitrite is removed, acid secretion rate and fluorescence (AO concentration in the mucosal medium) increase simultaneously and transiently. The net amount of AO released from the tissue is proportional to the net amount of acid released. Stimulation by secretagogue in basally secreting tissue causes synchronous transient increases in acid secretion rate and fluorescence. We conclude that accumulation of AO provides evidence for the existence of an intracellular storage pool of free protons within the transporting epithelium.

Acridine Orange↗
PubMed1988

Interactions of chloride and amiloride with the renal Na+/H/ antiporter.

Amiloride is a reversible inhibitor of the Na+/H+ antiporter which acts at the external aspect of the transport system. The kinetics of inhibition of the Na+/H+ antiporter with amiloride have been controversial, with the usual finding of simple competitive inhibition, but with other reports of mixed and noncompetitive inhibition of the transporter by amiloride. The present experiments demonstrate that the chloride content of the external transport buffer affects the kinetics of amiloride inhibition. Either simple competitive or mixed inhibition by amiloride was observed in the same vesicle preparations depending on the presence of chloride or gluconate in the buffer. The effect of chloride on the inhibitory effect of amiloride was dependent on the concentration of chloride and amiloride. Similar effects were observed with more potent analogues of amiloride. These findings suggest that the external aspect of the antiporter has a site or sites at which the inhibitory effects of amiloride on the Na+/H+ antiporter can be modified by chloride, even though chloride has only slight effects on the kinetics of the Na+/H+ antiporter in the absence of amiloride.

Amiloride↗
PubMed1986

Parathyroid hormone inhibition of Na+-H+ antiporter activity in a cultured renal cell line.

The renal effects of parathyroid hormone (PTH) include a decreased rate of acidification by the proximal tubule. To determine whether this effect represented a PTH action on the Na+-H+ antiporter, we investigated the effect of PTH on the established opossum kidney (OK) cell line. This cell line retains several features characteristic of proximal tubule cells, including an amiloride-sensitive Na+-H+ antiporter and high-affinity PTH receptors with a coupled cAMP response. We measured steady-state intracellular pH and amiloride-sensitive 22Na+ uptake as a reflection of the activity of the Na+-H+ antiporter. Under bicarbonate and CO2-free conditions, the steady-state intracellular pH of OK cell cultures was modified by altering the rate of Na+-H+ exchange. When Na+-H+ exchange was inhibited by amiloride, intracellular pH fell. Conversely, augmenting antiporter activity by addition of monensin, a Na+-H+ exchange ionophore, raised intracellular pH. PTH (2.5 X 10(-8) M) lowered intracellular pH by up to 0.17 pH units, and half of the maximum PTH effect was present at a concentration of 10(-12) M. This effect was not seen in the presence of amiloride or in the absence of sodium, suggesting that a functional Na+-H+ antiporter is necessary for its expression. The decrease in intracellular pH was reproduced by forskolin and 8-bromo-cAMP, suggesting that this is a cAMP-mediated effect. PTH, forskolin, and 8-bromo-cAMP also decreased the amiloride-sensitive component of 22Na+ uptake in OK cells by up to 64%, whereas the amiloride-insensitive component was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1979

Carbonic anhydrase-dependent bicarbonate reabsorption in the rat proximal tubule.

The extent to which bicarbonate reabsorption in the rat proximal convoluted tubule depends on carbonic anhydrase has been examined by in vivo microperfusion and the measurement of total CO2 concentration by microcalorimetry. Tubules were perfused with an ultrafiltrate-like solution at 13 nl/min, and volume reabsorptive rate (JV) was measured using [14C]inulin. Addition of either 800 or 100 microM acetazolamide to the perfusion solution completely inhibited the reabsorption of total CO2. The control total CO2 reabsorptive rate (JtCO2) was 147 +/- 23 pmol/mm.min, and acetazolamide reduced JtCO2 to -3 +/- 5 pmol/mm.min. Acetazolamide reduced JV by 65% from a control of 2.3 +/- 0.4 to 0.8 +/- 0.1 nl/mm.min. The dose-response curve for acetazolamide showed that the I50 for inhibition of JtCO2 was 4 microM. The inactive congener of acetazolamide, t-butyl acetazolamide, did not reduce JV or inhibit bicarbonate reabsorption, indicating that the effect of acetazolamide on JtCO2 was specific for carbonic anhydrase inhibition. Since bicarbonate reabsorption was completely blocked by carbonic anhydrase inhibition, there is no need to postulate either carbonic acid recycling or carbonic anhydrase-independent bicarbonate reabsorption.

Acetazolamide↗
PubMed1979

Effects of anion-transport inhibitors on NaCl reabsorption in the rat superficial proximal convoluted tubule.

The effects of anion-transport inhibitors on volume reabsorption, and total CO(2) concentrations were examined by in vivo microperfusion of superficial proximal convoluted tubules of rats. The luminal perfusion solution was a high-chloride, low-bicarbonate solution like that in the in vivo late proximal tubule. The anion-transport inhibitors were only added to the luminal perfusion solutions. In tubules perfused with the control high-chloride solution, the rate of volume reabsorption (J(v)) was 2.3+/-0.2 nl/mm.min (n = 18), and the collected total CO(2) concentration was 4.0+/-0.3 mM. Furosemide (3 mM) caused a marked reduction in volume reabsorption to 0.8+/-0.3 nl/mm.min (n = 20) and only a slight increase in the total CO(2) concentration of collected samples of perfusate (7.8+/-0.5 mM). 0.8 mM acetazolamide caused a more pronounced rise in the collected total CO(2) concentrations to 10.7+/-0.5 mM but only a slight fall in J(v) to 1.7+/-0.3 nl/mm.min (n = 19). Hence, we inferred that inhibition of carbonic anhydrase only partially accounted for the inhibition of J(v) by furosemide. 4-acetamido-4'-iso-thiocyanato-stilbene-2,2'-disulphonic acid (0.1 mM), a well-characterized inhibitor of erythrocyte anion exchange mechanisms, also reduced J(v) to 1.6+/-0.3 nl/mm.min (n = 15) without changing the total CO(2) concentrations of the collected perfusates (3.6+/-0.4 mM). The effect of 4-acetamido-4'-iso-thiocyanato-stilbene-2,2'-disulphonic acid on volume reabsorption could not be explained by carbonic anhydrase inhibition because there was no increase in the total CO(2) concentration of the collected fluids. Furosemide did not significantly inhibit the rate of tracer glucose efflux out of the tubules, which suggests that the effect of furosemide on volume reabsorption was not a result of some nonspecific depression of active sodium transport. These results are discussed with respect to the possible effects of anion-transport inhibitors on the paracellular shunt pathway, active sodium reabsorption, and neutral sodium chloride transport.

Absorption↗
PubMed1978

Occupancy of aldosterone binding sites in rat kidney cytosol.

The binding sites for aldosterone and a potent aldosterone antagonist (SC-26304) were studied in kidney cytosol from adrenalectomized rats. Preformed cytosol and kidney slices were incubated with 3H-labeled steroids in a wide range of concentrations. The recovery and characteristics of the binding sites were affected by the incubation and homogenization conditions. High-affinity, Type I mineralocorticoid binding was reduced by more than 95% when cytosol was incubated at 25 degrees C in the presence of calcium. Tissue dilution also affected the binding sites. SC-26304 was bound to high- and low-affinity receptors, similar to the binding of aldosterone. The physiologic response to aldosterone could result from binding to either or both sets of sites. Some of the physiologic responses to spirolactones could represent antagonism of the binding of aldosterone to either or both sites. A convenient method is presented for describing the relative occupancy of several different sites by any particular steroid.

Adrenalectomy↗
PubMed1978

Contribution of leaked load to solute transport by renal tubules.

Renal tubules reabsorb solutes from the glomerular filtrate. The relationship between "filtered load" and reabsorption has been previously discussed and analyzed in detail. One aspect which has not been emphasized, however, is that, when reabsorption of a solute causes its concentration (or activity) in the tubule lumen to decrease below the level in the blood, solute may enter the tubule down this concentration gradient adding a "leaked load" to the filtered load. The leaked load should be taken into account when quantifying tubular transport. In the present study we derived equations for estimating the leaked load and its contribution to transport. The importance of the leaked load of glucose in the rabbit proximal convoluted tubules is evaluated with parameters derived from in vitro perfusion and by solving the equations numerically. It is shown that, depending on the conditions, the leaked load of glucose may account for a substantial part of the glucose present in the tubule lumen and reabsorbed from the tubule. Also, the leaked load could conceivably be an important factor in the transport of other solutes such as lactase and bicarbonate in proximal tubules.

Animals↗
PubMed1978

Ion selectivity and proximal salt reabsorption.

Electrophysiological techniques were used in isolated perfused superficial (S) and juxtamedullary (JM) rabbit proximal convoluted tubules (PCT) to examine the relative sodium-to-chloride (PNa/PCl) and bicarbonate-to-chloride (PHCO3/PCl) permeability ratios. We found that the great majority of PCT are sodium selective and that PHCO3/PCl depends on the experimental conditions. In the presence of active sodium transport, PHCO3/PCl is high and increases with PNa/PCl. When PHCO3/PCl is determined after inhibition of active sodium transport or at 25 degrees C, PHCO3/PCl approximates the free solution anion mobility ratio of 0.5 and is independent of PNa/PCl. The difference between PHCO3/PCl determined in the presence of and in the absence of active transport suggests that the lowering of bath bicarbonate concentration in the presence of active transport changes both paracellular and transcellular current flow. In addition, we found that during luminal perfusion with high chloride, low bicarbonate, organic solute-free solutions, the transepithelial electrical potential depends on PNa/PCl and PHCO3/PCl. This potential is approximately 4.0 mV in S PCT with low PNa/PCl and falls progressively to zero in JM PCT with high PNa/PCl. From these data we conclude that anion concentration gradients drive an important diffusive flux of sodium chloride through the paracellular pathway only in PCT with low PNa/PCl ratios.

Animals↗