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Papers by Carol Whitfield

Blood, Feb 1, 1991

Human progenitor-derived erythroblasts have been recently shown t o respond t o erythropoietin (E... more Human progenitor-derived erythroblasts have been recently shown t o respond t o erythropoietin (Epo) with an increase in intracellular free calcium concentration [Ca,]. To explore the role of guanosine triphosphate (GTP)-binding proteins in mediating the rise in [CaJ, single day 10 erythroid burst forming unit (BFU-E)-derived erythroblasts loaded with Fura-2 were pretreated with pertussis toxin (PT), stimulated with Epo, and [Ca,] measured over 18 minutes with fluorescence microscopy coupled t o digital video imaging. The [Ca,] increase in day 10 erythroblasts stimulated with Epo was blocked by pretreatment with PT in a dose-dependent manner but not by heat-inactivated PT. These observations provided strong evidence that a PT-sensitive GTP-binding protein is involved. To further characterize the GTP-binding protein, day 10 erythroblast membrane preparations were solubilized, electrophoresed, and immunobloted with antibodies specific for the known PT-sensitive G-protein subunits: the three subtypes of G , (1.

Journal of Molecular and Cellular Cardiology, Dec 1, 1984

methylglucose into hearts of chronic diabetic rats was studied to determine if loss of transporte... more methylglucose into hearts of chronic diabetic rats was studied to determine if loss of transporter activity could be accounted for by higher concentrations of citrate and triglyceride and to determine if 7 days post alloxan was a representative time period for study of myocardial changes in chronic diabetes. Chronic diabetes was induced in rats by rapid i.v. injection of alloxan (37.5 mg/kg body weight), and the rats were studied 1 to 5 weeks afterward. Basal sugar transport rate in isolated perfused hearts declined after 2 weeks of diabetes and was nearly undetectable at 3 to 5 weeks. Stimulation of transport by insulin was also very low. Triglyceride concentrations were 50% of normal and G6P concentrations were elevated, but citrate concentrations were not different from control. Results of these studies showed that tissue triglyceride and citrate concentrations were not correlated with transport inhibition in chronic diabetic rat hearts. Loss of basal transport activity and lowered insulin sensitivity in these hearts is more likely due to a loss of transporters from the sarcolemma. These studies also show that transport rate and metabolite concentrations continue to change over 5 weeks of diabetes, and, therefore, one time point cannot be defined as representative of chronic diabetes.

Journal of Biological Chemistry, Jul 1, 1974

Abstract Epinephrine accelerated the carrier-mediated transport of 3-O-methylglucose and galactos... more Abstract Epinephrine accelerated the carrier-mediated transport of 3-O-methylglucose and galactose into avian erythrocytes. The magnitude of the effect was dependent upon the period of exposure and the concentration of epinephrine. With 0.1 mm epinephrine, 45 min were required for a significant increase in rate. After 60 min of exposure, a maximal effect was obtained with 0.4 mm epinephrine. Catechol, dopamine, norepinephrine, dl-isoproterenol, and ephedrine also increased transport rate. The stimulatory effect of epinephrine was partially blocked by desmethylimipramine and omission of extracellular potassium, but was unaffected by iproniazid (10 mm), β-thujaplicin (0.2 mm), propranolol (0.1 mm), or phentolamine (0.1 mm). Addition of a higher concentration (1 mm) of propranolol accelerated 3-O-methylglucose transport. Cyclic adenosine 3' : 5'-monophosphate or its dibutyryl derivative did not increase transport rate when added to the incubation medium. Addition of 1 mm propranolol lowered levels of cyclic adenosine 3' : 5'-monophosphate in control and epinephrine-treated cells, but stimulated the control rate of sugar entry. In contrast to the stimulatory effects on transport of nonmetabolized sugars, epinephrine was ineffective in accelerating glucose uptake. Incubation of avian erythrocytes in buffer containing epinephrine, but not glucose, led to more rapid consumption of ATP, while inclusion of glucose maintained ATP levels either in the presence or absence of the catecholamine. These studies indicate that the acceleration of sugar transport in avian erythrocytes by epinephrine may be related to depletion of cellular ATP.

Critical Reviews In Biochemistry And Molecular Biology, 1988

Erythrocyte spectrin is the major component of a skeletal protein meshwork which lines the cytopl... more Erythrocyte spectrin is the major component of a skeletal protein meshwork which lines the cytoplasmic surface of the red cell membrane. This structure has been termed the membrane skeleton in order to distinguish it from cytoskeletal structures which traverse ...

Federation Proceedings, 1975

Background: Sensitive skin usually manifests itself as unpleasant sensations and sometimes erythe... more Background: Sensitive skin usually manifests itself as unpleasant sensations and sometimes erythema. There are various triggering factors for this condition. Although sensitive skin may alter quality of life, its burden has not yet been explored. Objective: The aim of this study was to develop and validate a specific sensitive skin burden questionnaire called the BoSS (Burden of Sensitive Skin). Methods: A conceptual phase was developed, followed by a development phase, external validation, psychometric analysis, test-retest analysis and, finally, a translation, cross-cultural adaptation and cognitive debriefing. Results: A total of 6471 individuals participated in the study (4614 people in the validation study). The dimensionality of items was evaluated using factor analyses, suggesting three dimensions (selfcare, daily life, and appearance). Unidimensionality was confirmed by higher-order factor analysis.

Simulation in healthcare : journal of the Society for Simulation in Healthcare, 2009

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Biochimica Et Biophysica Acta - Biomembranes, Oct 1, 1977

The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic ... more The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic and anaerobic conditions. In anaerobic cells, transport measurements with 3-O-[~4C] methylglucose resulted in a set of similar dissociation-like constants. Thus the Michaelis constants of 3-O-['4C]methylglucose entry and exit, Kso and Ksi, were 8 and 7 raM, respectively. The equilibrium exchange constant, Bs, and the counterflow constant, Rs, were 9 and 11 mM, respectively. The activity constant for 3-O-methylglucose transport, Fs, defined as V/Km, was 4 ml/h per g. This set of kinetic constants was compatible with a symmetrical mobile-carrier model. In contrast, the Michaelis constant for glucose entry, K~o, was 2 mM and less than the counterflow constant, Ru (8 mM). This result could be accounted for by slower movement of the glucose-carrier complex than the free carrier. The activity constant for glucose transport, Fa, was 5 ml/h per g. Under aerobic conditions, two of the dissociation-like constants (K~i and B~) for 3-O-methylglucose transport were significantly larger than those obtained in anaerobic cells, but the remaining two (K~o and Rs) remained unchanged. The values for K~o, Ksi, Bs and R~ were 8, 26, 20 and 8 mM, respectively. The activity constant, F~, decreased Lo 2 ml/h per g. These changes in kinetic constants were consistent with the hypothesis that anoxia accelerated sugar transport by releasing free carrier that was previously sequestered on the inside of the cell membrane.

Biochemical and Biophysical Research Communications, Dec 1, 1970

Peak intraventricular pressure and rate of pressure development were lower in hearts from hypophy... more Peak intraventricular pressure and rate of pressure development were lower in hearts from hypophysectomized as compared to normal rats. Treatment of hypophysectomized rats with growth hormone (GH) and thyroxine (T 4 ) increased heart size, but only T 4 restored hemodynamic ...

Biochimica Et Biophysica Acta - Biomembranes, Apr 1, 1973

1. Simple anoxia, without addition of metabolic poisons, was found to stimulate carrier-mediated ... more 1. Simple anoxia, without addition of metabolic poisons, was found to stimulate carrier-mediated sugar transport. 2. Development of an anoxic stimulation of transport immediately followed changes in intracellular levels of low and high energy intermediates, suggesting a role for these compounds as regulators of transport. 3. Adenine and ATP were the only metabolites found to alter transport rates, when they were added exogenously. Adenine partially inhibited the anoxic stimulation of transport while ATP stimulated sugar entry in both aerobic and anaerobic cells. 4. Neither monovalent nor divalent cations were absolutely required for the development of the faster rate of transport in anoxic cells.

American Journal of Physiology-cell Physiology, Jul 1, 1981

Goose red blood cells were studied as a model for metabolic regulation of sugar transport. In con... more Goose red blood cells were studied as a model for metabolic regulation of sugar transport. In contrast to their action in human erythrocytes, sulfhydryl-blocking agents such as N-ethylmaleimide (NEM) stimulated 3-O-methylglucose transport markedly in goose red blood cells. The effect of NEM was further enhanced when adenosine 5'-triphosphate (ATP) was first depleted by 2,4-dinitrophenol treatment or anoxia. Only sulfhydryl-blocking agents that enter the cell were effective transport stimulators, and the effect was not altered by substrates of the transporter. In nucleated red blood cell ghosts, NEM inhibited 3-O-methylglucose transport. Results of these studies with intact cells were consistent with the hypothesis that free sulfhydryl groups are essential for regulation of transporter activity rather than for the transport process itself. The locus of NEM action appears to be either on the cytoplasmic side of the membrane or partially located in the cytoplasm. ATP depletion may expose previously masked sulfhydryl groups, producing an enhanced reaction with sulfhydryl-blocking agents and a highly stimulated rate of sugar transport.

American Journal of Physiology-endocrinology and Metabolism, 1978

Insulin increased the maximal rate of sugar transport in the perfused rat heart, but had essentia... more Insulin increased the maximal rate of sugar transport in the perfused rat heart, but had essentially no effect on the Michaelis constant of sugar entry or half-maximal constant for equilibrium exchange. In control hearts, the following kinetic parameters of 3-O-methylglucose transport were measured: Michaelis constant for entry, 7-10 mM; equilibrium exchange constant, 7 mM; and activity constant (Vmax/Km) from 0.02 to 0.1 ml/g.min. In insulin-treated hearts, these values were 6 mM, 3 MM, and 2.2 ml/g.min, respectively. These changes in transport constants were consistent with a model in which 1) sequestered carrier was released by the hormone or 2) carrier movement, in all forms and directions, was accelerated. Measurements of glucose transport in control hearts indicated that the Michaelis constant for entry was 4 mM and the activity constant, 0.5 ml/g.min. In insulin-treated hearts, quantitation of transport parameters was prevented by accumulation of intracellular glucose.

Proceedings of the National Academy of Sciences of the United States of America, Mar 1, 1983

IgG autoantibodies in human serum selectively bind to a glycopeptide antigen that appears on sene... more IgG autoantibodies in human serum selectively bind to a glycopeptide antigen that appears on senescent and damaged cells in situ. We identified the membrane protein from which the senescent cell antigen is derived by using a phagocytosis-inhibition assay and immunoautoradiographic gel staining and electroblotting techniques. Results of the phagocytosis-inhibition assay revealed that only the purified transmembrane glycoprotein designated "band 3" and senescent cell antigen inhibited the phagocytosis of erythrocytes induced by IgG eluted from senescent erythrocytes. Purified spectrin, syndein, band 4.1, actin, glycophorin A, and intact or desialylated sialoglycoprotein periodic acid/Schiff (PAS) staining bands 1-4 containing glycophorins A, B, and C did not inhibit phagocytosis. Specific antibodies against the senescent cell antigen and erythrocyte band 3 were used to identify the membrane protein from which the senescent cell antigen is derived. Band 3-related polypeptides (Mrs 60,000,42,000, and 18-26,000) were identified in erythrocyte ghosts prepared in the presence of diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, and EDTA by immunoautoradiography with antiband 3. Antibodies to senescent cell antigen reacted with band 3 and the same lower Mr band 3-related polypeptides. Thus, the senescent cell antigen is immunologically related to band 3.

MedEdPORTAL, Feb 17, 2012

MedEdPORTAL® is the journal of teaching and learning resources published by the Association of Am... more MedEdPORTAL® is the journal of teaching and learning resources published by the Association of American Medical Colleges (AAMC) in partnership with the American Dental Education Association (ADEA).

Dissertation Abstracts: B, 1969

Blood, Mar 1, 1983

Two mammalian species (porcine and murine) have erythrocytes that are being widely used to study ... more Two mammalian species (porcine and murine) have erythrocytes that are being widely used to study membrane protein synthesis and red cell aging. Erythrocytes of these species however. are significantly smaller than those of the human. Before results obtained from study of these red cells can be applied to human cells. the membrane skeleton of these species must be investigated to determine if the skeletal elements are equivalent. Both pig and mouse bands 4.1 b were of lower molecular weight than human 4.lb. and the a/b ratio was lower. In each species. 4.la and b were sequence-related phosphoproteins. and yielded substantially different one-dimensional peptide maps.

Biochimica Et Biophysica Acta - Biomembranes, Jun 1, 1976

The technique of reversible hemolysis represents one approach which may be used to study transpor... more The technique of reversible hemolysis represents one approach which may be used to study transport regulation in nucleated red cells. After 1 h of incubation at 37 ~C, 88 i~,/, of the ghosts regained their permeability barrier to e-glucose. In these ghosts, the carrier-mediated rate of entry of 3-O-methylglucose was more than I 0-fold greater than the rate in intact cells. Glyceraldehyde-3-phosphate dehydrogenase prevented ghosts from resealing when it was present at the time of hemolysis. Albumin, lactic dehydrogenase and peroxidase did not have this effect. Sugar transport rate could not be tested in the unsealed ghosts. Two possible mechanisms for the effect of hypotonic hemolysis on sugar transport rate were discussed: (1) altered membrane organization and (2) loss ofintracellular compounds which bind to the membrane and inhibit transport in intact cells.

Archives of Biochemistry and Biophysics, Dec 1, 1978

Abstract Vinblastine and colchicine, compounds which effect the state of aggregation of microtubu... more Abstract Vinblastine and colchicine, compounds which effect the state of aggregation of microtubules, were investigated to determine if changes in the rate of sugar transport were produced by these compounds. Vinblastine accelerated 3-O-methylglucose entry into avian erythrocytes. At a concentration of 1.5 m m , transport was accelerated two-fold. The effect of vinblastine was not attributed to cell energy depletion or to increased entry by simple diffusion. Stimulation of transport did not require preincubation of the cells with vinblastine, and the effect was reversible. Colchicine (2 m m ) inhibited 3-O-methylglucose entry in aerobic or anoxic intact red cells and in red cell ghosts. A change in the state of aggregation or activity of the microtubular system could represent a model for regulation of a membrane carrier. The present results would lend support to this model.