Biomedical subjects

J D Kaunitz

Publications and source records attributed to J D Kaunitz.

45 records · Page 3Linked to original sources

PubMed1986

Identification of a vanadate-sensitive potassium-dependent proton pump from rabbit colon.

Membrane vesicles prepared from rabbit distal colon were used to study colonic transport mechanisms. Differential and sucrose-Ficoll density gradient centrifugation of the mucosal homogenate yielded fractions which supported ATP-dependent proton transport, as measured with the fluorescent weak base acridine orange. Quenching of acridine orange absorbance in light microsomes and microsome-derived density gradient fractions was MgATP-dependent and was reversed with nigericin; these characteristics suggest the presence of one or more ATP-driven proton pumps. Proton transport in the microsomal fraction was inhibited by N-ethylmaleimide more than by orthovanadate, and was dependent on extravesicular chloride. Vesicles in a microsome-derived gradient fraction were inhibited by orthovanadate more than by N-ethylmaleimide. N-ethylmaleimide pretreatment of this gradient fraction uncovered a vesicle population with characteristics similar to the gastric H+,K+ATPase: proton transport was abolished by orthovanadate and the experimental anti-ulcer drug SCH 28080, was enhanced by potassium, and was not affected by chloride. ATP-generated proton gradients in this fraction were not dissipated by the proton ionophore 3,3',4',5-tetrachlorosalicylanilide. We conclude that two ATP-driven proton pumps are present in mucosa from distal rabbit colon; one with characteristics of N-ethylmaleimide-sensitive organelle associated proton pumps, and one similar to the gastric proton-potassium exchanger.

Adenosine Triphosphatases↗

PubMed1985

Characterization of an electrogenic ATP and chloride-dependent proton translocating pump from rat renal medulla.

To study acidification mechanisms in the distal nephron, microsomes were prepared from rat renal medulla by differential centrifugation. Microsomes were enriched in the enzyme marker gamma-glutamyl transferase and contained an ATP-dependent proton pump, as evidenced by ATP-dependent, 3,3',4',5-tetrachlorosalicylanilide-reversible quenching of acridine orange fluorescence. Acidification was vanadate-insensitive, but was completely inhibited by micromolar N-ethylmaleimide. Maximal acidification was achieved in the presence of halide (Cl-, Br-) only and was not attainable with potassium-valinomycin diffusion potentials without halide ion. Microsomal ATPase activity was neither chloride- nor N-ethylmaleimide-sensitive. A chloride conductance was observed only with vesicles which had undergone ATP-dependent acidification. An ATP-dependent, N-ethylmaleimide-inhibitable, 3,3',4',5-tetrachlorosalicylanilide-reversible, and chloride-attenuated quench of bis(1,3-dibutylbarbituric acid-(5] pentamethinoxonol fluorescence was seen, consistent with net transfer of positive charge into the vesicles. Nonetheless, positive intravesicular potentials increased the ATP-dependent initial acidification rate, perhaps by increasing availability of chloride ion to the transport site. Our results are consistent with an electrogenic, ATP-dependent proton pump regulated by a voltage-sensitive chloride site.

Adenosine Triphosphatases↗

PubMed1985

pH gradient-dependent increased Na+-H+ antiport capacity of the rabbit remnant kidney.

The adaptative response of the renal proximal tubule to a reduction of renal mass was studied in brush border membrane vesicles prepared from the solitary remnant kidney (RK) of subtotally nephrectomized rabbits. The in vivo acid-base status of RK and sham-operated controls (SK) was similar. In the absence of organic solutes, Na+ flux across the membrane demonstrated features of Na+-H+ antiport, i.e., stimulation by a transmembrane pH gradient and inhibition by amiloride. Kinetic parameters for Na+-H+ antiport were derived with different experimental protocols. In the presence of an opposing H+ gradient and over a limited range of Na+ concentration, JNamax was enhanced 65% in RK vesicles compared with SK vesicles and KtNa was unchanged. The enhanced JNamax was not apparent under H+ equilibrium conditions, Comparable values for JNamax and KtNa were obtained by studying RK vesicles at external Na+ concentrations of 0-200 mM and resolving uptake into a substrate component, representing Na+-H+ antiport, and a nonsaturable diffusive component. The apparent Na+ permeability (P'Na) of RK vesicles was identical to the P'Na of normal kidney vesicles, under both H+ gradient and H+ equilibrium conditions. H+ permeability, measured with acridine orange, was also the same in RK and SK vesicles. These studies demonstrate that in the remnant kidney model of chronic renal insufficiency there is an increase in the JNamax of the Na+-H+ antiporter in the luminal membrane of the proximal tubule that is revealed only under transmembrane H+ gradient conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗

PubMed1984

Kinetics of sodium D-glucose cotransport in bovine intestinal brush border vesicles.

Brush border membrane vesicles ( BBMV ) purified from steer jejunum were used to study the kinetics of sodium D-glucose cotransport under voltage clamped, zero-trans conditions. When the initial rate of glucose transport ( Jgluc ) was measured over a wide range of glucose concentrations ([S] = 0.01-20 mM), curvature of the Woolf - Augustinsson -Hofstee plots was seen, compatible with a diffusional and one major, high capacity (maximal transport rate Jmax = 5.8-8.8 nmol/mg X min) saturable system. Further studies indicated that changes in cis [Na] altered the Kt, but not the Jmax, suggesting the presence of a rapid-equilibrium, ordered bireactant system with sodium adding first. Trans sodium inhibited Jgluc hyperbolically, KCl-valinomycin diffusion potentials, inner membrane face positive, lowered Jgluc , while potentials of the opposite polarity raise Jgluc . At low glucose concentrations ([S] less than 0.05 mM), a second, minor, high affinity transport system was indicated. Further evidence for this second saturable system was provided by sodium activation curves, which were hyperbolic when [S] = 0.5 mM, but were sigmoidal when [S] = 0.01 mM. Simultaneous fluxes of 22Na and [3H]glucose at 1 mM glucose and 30 mM NaCl yielded a cotransport-dependent flux ratio of 2:1 sodium/glucose, suggestive of 1:1 (Na/glucose) high capacity, low affinity system and a approximately 3:1 (Na/glucose) high affinity, low capacity system. Kinetic experiments with rabbit jejunal brush borders revealed two major Na-dependent saturable systems. Extravesicular (cis) Na changed the Kt, but not the Jmax of the major system.

Animals↗

PubMed1984

Intestinal transport of amino acids and sugars: advances using membrane vesicles.

Glucose crosses the intestinal brush border via one diffusive and two saturable systems. Under zero-trans conditions, the major saturable system has the characteristics of an Iso Ordered Bireactant system with one Na binding and, additionally, shows the properties of trans inhibition by Na and sensitivity to Em. An additional high-affinity saturable system exists with a Kt in the micromolar range and has the capacity for binding multiple Na+ ions. Biochemical and transport studies indicate that the brush-border Na-glucose cotransporter may be asymmetric with respect to the inner and outer membrane face. The Na-independent glucose carrier found in enterocyte basolateral membranes strongly resembles the facilitated glucose carrier found in other membranes.

Amino Acids↗

PubMed1983

Kinetics of sodium succinate cotransport across renal brush-border membranes.

The kinetics of Na/succinate cotransport across renal brush-borders was studied using membrane vesicles. Initial rates of succinate uptake (Js) were estimated from 1-s uptakes measured under voltage-clamped conditions. Lowering the external (cis) sodium concentration reduced the succinate Kt without affecting the Jsmax. Increasing the intravesicular (trans) sodium concentration reduced both Jsmax and Kt. This trans inhibition by Na was relieved by trans-succinate. Varying the membrane potential from -60 to +60 reduced succinate transport in an exponential manner, which was reflected by a Kt effect, i.e. an increase in the Kt with no change in Jsmax. The membrane potential results suggest that the succinate/sodium-carrier complex bears a net positive charge. On the basis of these and earlier observations, we propose that Na/succinate cotransport across renal brush-borders is described by an Iso Ordered Quad Quad reaction kinetics in which three Na ions first bind to the carrier to increase its affinity for succinate.

Animals↗

PubMed1982

Involvement of multiple sodium ions in intestinal d-glucose transport.

Brush border membrane vesicles isolated from rabbit small intestine were used to measure the interactions between sodium and glucose transport with a rapid uptake technique. A plot of glucose uptake rate vs. increasing sodium concentration yielded a sigmoid curve. Hill analysis revealed a coefficient of 1.9 +/- 0.02 (+/- SEM), consistent with at least two sodium ions involved in glucose transport. Transport coupling was then measured directly with double-label experiments in which the uptakes of D-glucose and sodium were determined in the presence and absence of cotransported solute. At the earliest time point, the ratio of cosubstrate-dependent sodium transport to glucose transport was 3.2 +2- 0.7 (+/- SEM). We conclude that two or more sodium ions are coupled to glucose transport across the intestinal brush border membranes.

Animals↗

PubMed1977

The bioavailability of folic acid added to wine.

Folate deficiency is a frequent cause of anemia in alcoholics, but little attention has been paid to its prevention. Folic acid was readily soluble in wines of high ethanol content at concentrations of 10 microgram/ml. Lactobacillus casei folate activity of folic acid added to wines was well maintained during a month's storage at room temperature and fell to 61% to 66% of original activity after 3 months. Pteroylglutamic acid, 10 microgram/ml, added to wines and given in doses of the beverages (4 ml/kg body weight that caused inebriation, was well absorbed by six normal human volunteers (mean maximal increment in serum folate concentration +/- SEM, 71 +/- 8 ng/ml) and by seven recently intoxicated chronic alcoholics (mean increment, 94 +/- 4 ng/ml). Folate deficiency in alcoholics could be prevented by the fortification of alcoholic beverages with the vitamin.

Adult↗

PubMedDate not supplied

New insights into impairment of mucosal defense in portal hypertensive gastric mucosa.

Portal hypertension (PHT) increases susceptibility of the gastric mucosa to injury. The aim of this study was to investigate whether PHT affects rat gastric mucosal defense mechanisms in vivo at the pre-epithelial, epithelial, and/or post-epithelial levels. PHT was produced in rats by staged portal vein ligation and sham-operated (SO) rats served as controls. The gastric mucosa was exposed, chambered, and continuously superfused with buffers under in vivo microscopy. We measured gastric mucosal gel layer thickness, surface epithelial cell intracellular pH (pHi), mucosal blood flow, and mucosal/serosal oxygenation. In PHT rats, gastric mucosal gel layer thickness was significantly reduced (88 +/- 16 microm in PHT rats vs. 135 +/- 25 microm in SO rats; P <0.0001), and the surface epithelial cell pHi was significantly decreased (6.80 +/- 0.11 in PHT rats vs. 7.09 +/- 0.21 in SO rats; P <0.01). Although total gastric mucosal blood flow was significantly increased in PHT rats by 72% (P <0.05), the oxygenation of the gastric mucosal surface was decreased by 42% (P <0.05) compared with SO rats. PHT impairs pre-epithelial (mucosal gel layer thickness), epithelial (pHi), and post-epithelial (maldistribution of blood flow) components of the gastric mucosal barrier. These findings can explain the increased susceptibility of portal hypertensive gastric mucosa to injury.

Animals↗