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J D Gardner

Publications and source records attributed to J D Gardner.

At least 289 records · Page 16Linked to original sources
PubMed1974

Sequence of events mediating the effect of cholera toxin on rat thymocytes.

We have found that in rat thymocytes binding of [(125)I]choleragen is followed by cellular accumulation of cyclic 3',5'-AMP which, in turn, is followed by stimulation of amino acid transport. Binding of cholera toxin was complete by 30 min and remained constant for the subsequent 150 min. After stimulation by choleragen, cellular cyclic 3',5'-AMP became maximal by 30 min, after which it declined steadily so that by 90 min of incubation, cellular cyclic nucleotide levels were only 20% of those seen at 30 min. Stimulation of amino acid transport, although detectable by 15 min, did not become maximal until 120 min (by which time cellular cyclic 3',5'-AMP had decreased by more than 80%). We have also used this system to delineate the step at which various pharmacologic agents and hormones act to alter the sequence of events mediating the response of rat thymocytes to cholera toxin. The ability of cycloheximide to abolish choleragen-stimulated amino acid influx without reducing [(125)I]choleragen binding or cellular cyclic 3',5'-AMP suggests that cyclic nucleotide stimulation of amino acid transport includes a step involving protein synthesis.

Aminoisobutyric Acids↗
PubMed1973

Effects of digoxin-specific antibodies on accumulation and binding of digoxin by human erythrocytes.

THE PRESENT STUDIES INDICATE THAT ACCUMULATION OF DIGOXIN BY INTACT HUMAN ERYTHROCYTES IS THE RESULT OF TWO PROCESSES: binding of digoxin to the erythrocyte membrane and uptake of digoxin across the membrane into the cell. In contrast, accumulation of ouabain by human erythrocytes is entirely attributable to binding of this glycoside to the plasma membrane. Digoxin binding to the erythrocyte membrane involves a single class of binding sites, is a saturable function of the extracellular digoxin concentration, reversible, temperature-sensitive, dependent on the cation composition of the incubation medium, inhibited by other cardioactive steroids, and correlates with the inhibition of erythrocyte potassium influx. Digoxin uptake across the membrane into the cell is also temperature-sensitive and reversible but is a linear function of the extracellular digoxin concentration, not altered by changes in the cation composition of the incubation medium, not inhibited by other cardioactive steroids, and does not correlate with inhibition of erythrocyte potassium influx. Digoxinspecific antibodies can both prevent and reverse effects of digoxin on potassium influx in human erythrocytes by virtue of the capacity of the antibodies to decrease the amount of digoxin that is bound to the erythrocyte membrane. These antibodies also reduce uptake of digoxin across the plasma membrane into the erythrocyte; however, this portion of cellular digoxin is not responsible for the observed inhibition of potassium influx. In the presence of digoxin-specific antibodies, the changes in digoxin binding to the erythrocyte membrane and in digoxin uptake across the membrane into the cell reflect the ability of the antibodies to form complexes with "free" digoxin molecules in the incubation medium and thereby decrease the effective concentration of digoxin.

Adult↗
PubMed1973

Ouabain binding and cation transport in human erythrocytes.

In the present studies we have explored the relation between ouabain binding and the inhibition of potassium influx in intact human erythrocytes. The rate at which bound ouabain molecules dissociate from the erythrocyte membrane is not altered by complete replacement of choline with sodium or by partial replacement with potassium. These findings indicate that the effects of these cations on ouabain binding reflect alterations in the rate of association of ouabain molecules with the erythrocyte membrane. Variations in the cation composition of the incubation solution did not alter the relation between the fraction of the glycosidebinding sites occupied by ouabain or the fraction of ouabain-sensitive potassium influx which was inhibited. That is, irrespective of the affinity of the erythrocyte membrane for ouabain molecules and irrespective of the magnitude of glycoside-sensitive potassium influx, occupation of a given fraction of the glycoside-binding sites by ouabain results in the inhibition of an equal fraction of the ouabain-sensitive potassium transport sites.

Adult↗
PubMed1972

The effects of sodium and potassium on ouabain binding by human erythrocytes.

Ouabain binding by the human erythrocyte membrane is reversible, exhibits a high degree of chemical specificity, and can be detected at ouabain concentrations as low as 1 x 10(-10)M. The relation between ouabain binding and ouabain concentration can be described by a rectangular hyperbola permitting determination of the maximal binding (B(max)) and the ouabain concentration at which ouabain binding is half-maximal (K(B)). Reducing the external sodium concentration increased K(B), while reducing the external potassium concentration decreased K(B). Neither cation altered B(max) The reciprocal of K(B) was a linear function of the sodium concentration at sodium concentrations ranging from 0 to 150 mM. Conversely, the relation between the reciprocal of K(B) and the external potassium concentration was nonlinear, and raising the potassium concentration above 4 mM produced no further increase in K(B). These results are compatible with a model which postulates that the erythrocyte membrane contains a finite number of receptors each composed of a glycoside-binding site and a cation-binding site. When sodium occupies the cation-binding site, the affinity of the glycoside site for ouabain is increased; when potassium occupies the cation-binding site the affinity of the glycoside site for ouabain is decreased.

Adolescent↗
PubMed1972

Altered membrane sodium transport in Bartter's syndrome.

To explore the possibility that Bartter's syndrome is the manifestation of an inherited abnormality of sodium transport, we have measured various parameters of sodium transport in erythrocytes from patients with Bartter's syndrome, their siblings, and their parents. Sodium transport in six of the eight patients with Bartter's syndrome differed significantly from that in the other two patients. On the basis of this difference, the patients were divided into two groups (type I and type II). In the six type I patients, fractional sodium outflux (0.38+/-0.05/hr [SD]) was significantly less than normal (0.50+/-0.07) and erythrocyte sodium concentration (9.48+/-0.84 mmoles/liter cells per hr) was significantly greater than normal (5.24+/-0.66). In the two type II patients, none of the measured parameters of sodium transport differed significantly from normal. Erythrocyte sodium transport in the relatives of three type I patients was altered in a way similar to that in the type I patients and was significantly different from that in the relatives of a type II patient. These findings indicate the presence of inherited alterations of erythrocyte sodium transport in certain patients with Bartter's syndrome.

Adolescent↗