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D C Tosteson

Publications and source records attributed to D C Tosteson.

105 records · Page 6Linked to original sources
PubMed1967

The effect of valinomycin on potassium and sodium permeability of HK and LK sheep red cells.

A cyclic depsipeptide antibiotic, valinomycin, was found to produce increased selective permeability of the plasma membranes of HK and LK sheep red blood cells to potassium but not to sodium ions. The compound had relatively little effect on the active extrusion of sodium from HK sheep red blood cells or on the Na + K-stimulated ATPase activity of membranes derived from these cells. It is proposed that the selective cation permeability produced by this compound depends primarily on steric factors, particularly the relationship between the diameter of the ring and the effective diameter of the ion. The significance of these results for the problem of the mechanism of ionic selectivity in natural membranes is discussed.

Adenosine Triphosphatases↗
PubMed1967

The effect of valinomycin on the ionic permeability of thin lipid membranes.

Optically black membranes prepared from sheep red cell lipids have a high electrical resistance (1-3 x 10(8) ohm-cm(2)). The ionic transference numbers (T(i)) for cations (Na(+) or K(+)) are equal to each other but at least four to five times greater than for Cl(-). The cyclic depsipeptide valinomycin produces a striking decrease in the membrane resistance when K(+), but not when Na(+) is in the solutions bathing the membrane. The ratio T(Na)/T(K), estimated from membrane voltages in the presence of ionic concentration gradients, approaches zero. The order of membrane monovalent cation selectivity, in the presence of valinomycin, is H(+) > Rb(+) > K(+) > Cs(+) > Na(+). Addition of the antibiotic to one side of a membrane which separates identical solutions of NaCl produces a substantial (up to 80 mV) membrane voltage (side opposite valinomycin negative). These data are consistent with the hypothesis that valinomycin can interact with appropriately sized cations (hydrated diameter ??? 6 A) to increase their membrane permeability, perhaps by forming hydrogen bonds between the solvation shell of the cations and carbonyl oxygens in the valinomycin molecule which are directed toward the aperture of the ring.

Animals↗
PubMed1967

The formation and properties of thin lipid membranes from HK and LK sheep red cell lipids.

Lipids were obtained from high potassium (HK) and low potassium (LK) sheep red cells by sequential extraction of the erythrocytes with isopropanol-chloroform, chloroform-methanol-0.1 M KCl, and chloroform. The extract contained cholesterol and phospholipid in a molar ratio of 0.8:1.0, and less than 1% protein contaminant. Stable thin lipid membranes separating two aqueous compartments were formed from an erythrocyte lipid-hydrocarbon solution, and had an electrical resistance of approximately 10(8) ohm-cm(2) and a capacitance of 0.38-0.4 microf/cm(2). From the capacitance values, membrane thickness was estimated to be 46-132 A, depending on the assumed value for the dielectric constant (2.0-4.5). Membrane voltage was recorded in the presence of ionic (NaCl and/or KCl) concentration gradients in the solutions bathing the membrane. The permeability of the membrane to Na(+), K(+), and Cl(-) (expressed as the transference number, T(ion)) was computed from the steady-state membrane voltage and the activity ratio of the ions in the compartments bathing the membrane. T(Na) and T(K) were approximately equal ( approximately 0.8) and considerably greater than T(Cl) ( approximately 0.2). The ionic transference numbers were independent of temperature, the hydrocarbon solvent, the osmolarity of the solutions bathing the membranes, and the cholesterol content of the membranes, over the range 21-38 degrees C. The high degree of membrane cation selectivity was tentatively attributed to the negatively charged phospholipids (phosphatidylethanolamine and phosphatidylserine) present in the lipid extract.

Animals↗
PubMed1966

Cytodifferentiation and membrane transport properties in LK sheep red cells.

Young cells produced in LK sheep during rapid hematopoiesis after massive hemorrhage contain more K than the cells which are normally released into the circulation. The K content in these new cells falls to that characteristic of mature LK cells after a few days in the circulation. K transport properties in young and old cells before and after massive bleeding were studied. Young and old cells were separated by means of a density gradient centrifugation technique. Evidence showing that younger cells are found in the lower density fractions is presented. Active transport of K in the lightest fraction as measured by strophanthidin-sensitive influx was four to five times greater in red cells drawn 6 days after massive bleeding while the K leak as measured by strophanthidin-insensitive influx was only slightly larger. No change after bleeding was observed in older cells which had been present in the circulation prior to the hemorrhage. It is concluded that the high K content of young cells produced in LK sheep after bleeding is due to temporary retention of membrane K transport properties characteristic of HK cells. Thus, genetically determined modification of membrane transport properties has been shown to occur in nondividing circulating red cells.

Animals↗
PubMed1965

Separation of adenosine triphosphatase of HK and LK sheep red cell membranes by density gradient centrifugation.

Membrane fragments from high potassium (HK) and low potassium (LK) sheep red cells were separated by density gradient centrifugation. Three preparations were studied: (1) HK membranes sonicated for 20 minutes, (2) HK membranes sonicated for 3 minutes, and (3) LK membranes sonicated for 3 minutes. The adenosine triphosphatase (ATPase) activity in the maximally disrupted preparation (1) was not sensitive to Na + K and was recovered in relatively small but heavy (specific gravity 1.19) fragments which made up no more than 8 per cent of the total membrane. Both Na + K-sensitive (S) and Na + K-insensitive (I) ATPase activity were found in the more gently broken up preparations (2) and (3) but the ratio of S- to I-ATPase was much greater in HK than in LK membrane fragments. S-ATPase activity in preparation (2) was about 50 per cent that observed in HK membranes prior to sonication. S-ATPase activity was recovered from the density gradient in relatively large but light (specific gravity 1.10) fragments. As was the case with the maximally disrupted preparation (1), I-ATPase activity in both preparations (2) and (3) was recovered in small but heavy (specific gravity > 1.20) fragments. The possibility that sensitivity of sheep red cell membrane ATPase to Na + K depends on the association between units containing the enzyme(s) and large, light, phospholipid-containing components is discussed.

Adenosine Triphosphatases↗
PubMedDate not supplied

Red cell lithium-sodium countertransport and sodium-potassium cotransport in patients with essential hypertension.

Alterations in sodium countertransport and cotransport have been reported in red cells of patients with essential hypertension. We have investigated the relationship between these two systems by performing simultaneous measurements of the maximal rates of lithium-sodium (Li1-Na0) countertransport and outward sodium-potassium (Na-K) cotransport in red cells from normotensive and hypertensive subjects. Li1-Na0 countertransport was assayed by measuring the Na0-stimulated Li efflux from cells loaded to contain 10 mmoles Li per liter of cells by incubation in isotonic LiCl. Na-K cotransport was assayed by measuring the furosemide-sensitive component of Na and K efflux into magnesium-sucrose medium from cells loaded by the p-chloromercuribenzene sulfonic acid (PCMBS) procedure to obtain 50 mmoles of both ions per liter of cells. The mean values (+/- SE) for 16 normotensives and 22 hypertensives were (mmole/liter cells x hour): Na countertransport = 0.29 +/- 0.02 vs 0.51 +/- 0.03 (p less than 0.001); Na cotransport = 0.30 +/- 0.03 vs 0.51 +/- 0.05 (p less than 0.005); and K cotransport = 0.34 +/- 0.03 vs 0.60 +/- 0.04 (p less than 0.005). Li1-Na0 countertransport correlated significantly with Na cotransport (r = 0.50, n = 38, p less than 0.005) and K cotransport (r = 0.57, p less than 0.005). This observation suggests that both transport systems are somehow regulated to be more active in this group of hypertensive patients. The increased cotransport in hypertensive patients is also apparent from two other measurements of Na and K fluxes in red cells suspended in Na medium. First, the furosemide-sensitive net Na efflux into Na medium was (mean +/- SE) 0.25 +/- 0.05 in 10 normotensive subjects and 0.50 +/- 0.09 in 12 hypertensive patients. Second, the furosemide-sensitive net K efflux into Na medium was (mean +/- SE) 0.25 +/- 0.04 in 13 normotensive subjects and 0.43 +/- 0.04 in 16 hypertensive patients (p less than 0.005). We conclude that mean values for both Na countertransport and Na-K cotransport are significantly higher in the group of hypertensives than in the group of normal control subjects.

Biological Transport↗