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Biomedical subjects

J C Freedman

Publications and source records attributed to J C Freedman.

27 records · Page 2Linked to original sources
PubMed1979

Ionic and osmotic equilibria of human red blood cells treated with nystatin.

Human red blood cells have been incubated in the presence of nystatin, which allows Na and K, as well as Cl and pH to equilibrate rapidly when cell volume is set with external impermeant sucrose. The intracellular mean ionic activity coefficients, relative to values in the extracellular solution, for KCl and NaCl are 1.01 +/- 0.02 and 0.99 +/- 0.02 (SD, n = 10), respectively, and are independent of external pH, pH o, and of [sucrose]o. With nystatin the dependence of red cell volume on [sucrose]o deviates from ideal osmotic behavior by as much as a factor of three. A virial equation for the osmotic coefficient, phi, of human hemoglobin, Hb, accounts for the cell volumes, and is the same as that which describes Adair's measurements of phi Hb for Hb isolated from sheep and ox bloods. In the presence of nystatin the slope of the acid-base titration curve of the cells is independent of cell volume, implying that the charge on impermeant cellular solutes is independent of Hb concentration at constant pH. By modifying the Jacobs-stewart equations (1947. J. Cell. Comp. Physiol. 30: 79--103) with the osmotic coefficients of Hb and of salts, a nonideal thermodynamic model has been devised which predicts equilibrium Donnan ratios and red cell volume from the composition of the extracellular solution and from certain parameters of the cells. In addition to accounting for the dependence of cell volume on osmotic pressure, the model also describes accurately the dependence of Donnan ratios and cell volumes on pHo either in the presence or absence of nystatin.

Body Water↗
PubMed1979

The relation between dicarbocyanine dye fluorescence and the membrane potential of human red blood cells set at varying Donnan equilibria.

The fluorescence, F, of two dicarbocyanine dyes, diS-C3(5) and diI-C3(5), depends both on the membrane potential, E, and on the intracellular pH, pHc, or human red blood cells. Compositions of isotonic media have been devised in which the equilibrium Donnan potential, E, varies at constant pHc and in which pHc varies at constant E. Dye fluorescence measurements in these suspensions yield calibrations of +1.7 % delta F/mV for diS-C3(5) and +0.6 % delta F/mV for diI-C3 (5). While pHo does not affect F of either dye, changes in pHc of 0.1 unit at constant E cause changes of F equivalent to those induced by 2--3mV. Based on these results, a method is given for estimating changes in E from dye fluorescence in experiments in which E and pHc co-vary. The relation of F to E also depends in a complex way on the type and concentration of cells and dye, and the wavelengths employed. The equilibrium calibration of dye fluorescence, when applied to diffusion potentials induced by 1 microM valinomycin, yields a value for the permeability ratio, PK.VAL/PCl, of 20 +/- 5, in agreement with previous estimates by other methods. The calibration of F is identical both for diffusion potentials and for equilibrium potentials, implying that diC-C3(5) responds to changes in voltage independently of ionic fluxes across the red cell membrane. Changes in the absorption spectra of dye in the presence of red cells in response to changes in E show that formation of nonfluorescent dimers contributes to fluorescence quenching of diS-C3(5). In contrast, only a hydrophobic interaction of dye monomers need be considered for diI-C3(5), indicating the occurrence of a simpler mechanism of fluorescence quenching.

Cell Membrane Permeability↗
PubMedDate not supplied

Lack of erythrocyte superoxide dismutase change during human senescence.

Superoxide dismutase (SOD), widely distributed in aerobic organisms, catalyzes dismutation of the superoxide free radical, O2-, to oxygen and hydrogen peroxide and apparently protects against oxygen toxicity. In human erythrocytes, O2- arises from autoxidation of oxyhemoglobin and SOD activity is copper-dependent. Since human erythrocyte copper content has been reported to decline in the fifth decade of life, we investigated the age dependence of human erythrocyte SOD activity. The mean SOD activity, assayed by inhibition of epinephrine autoxidation, was 415 +/- 66 units/g cells or 50 +/- 11 units/mg non-Hb protein. No significant difference was observed between young and old adults, and no correlations were detected with sex, state of health of the donor, or with blood hemoglobin content. The lack of general decline of SOD activity with age narrows the possible mechanisms for an involvement of O2- in senescence. SOD may yet decline in other longer-lived tissues or, as suggested by Fridovich, a constant low level of damage may be caused by imperfect scavenging of O2- by SOD. If such a mechanism is operative, it appears not to affect synthesis of SOD in erythrocyte precursor cells into the eighth decade of human life.

Aging↗
PubMedDate not supplied

Cellular deformability of normoxic and hypoxic mammalian red blood cells.

The deformability of red blood cells is important in the microcirculation where capillary diameters are often smaller than those of the red blood cells. In the present study, ektacytometry was used to examine the effect of hypoxia on the deformability of red blood cells from five mammalian species: Human, cat, rat, rabbit, and dog. Deformability was characterized in both normoxic (PO2 = 129 +/- 6 mm Hg) and hypoxic (PO2 = 47 +/- 6 mm Hg) conditions in two different ways. First, we used the Elongation Index (EI) which quantitates the extent of elongation of red blood cells in response to increasing fluid shear stress; second, we used the Elongation Constant (EC), which quantitates the exponential dependence of the fraction of maximal elongation on the varying shear stress. The EI was measured at high shear stresses (150-250 dyn/cm2), as well as at lower shear stresses (15, 32 and 64 dyn/cm2) that occur in the microcirculation. In response to hypoxia at high shear stresses, the EI of the rat red blood cells decreased by 9.3% (P < 0.05), but was not altered in the other four species studied. Moreover, in all five species, the EC and EI at the lower shear stresses were unaltered in response to hypoxia. These ektacytometry experiments indicate that (1) the elongation constant is a new and useful parameter for characterizing the deformability of red blood cells and (2), the deformability of human, cat, dog, and rabbit red blood cells is unaltered by hypoxia. The results constrain the possible mechanisms that could account for the observation that hypoxia decreases the filterability of certain species of red blood cells, which was reported previously.

Animals↗