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C Washington

Publications and source records attributed to C Washington.

43 records · Page 3Linked to original sources
PubMed1988

Anion specificity of the jejunal folate carrier: effects of reduced folate analogues on folate uptake and efflux.

We previously reported that 3H-folate uptake by rabbit jejunal brush-border membrane (BBM) vesicles was markedly stimulated by an outwardly directed OH- gradient (pHin 7.7, pHout 5.5), inhibited by anion exchange inhibitors (DIDS, SITS, furosemide), and saturable (folate Km = 0.19 microM) suggesting carrier-mediated folate/OH- exchange (or H+/folate cotransport). In the present study, the anion specificity of this transport process was examined. Under conditions of an outwardly directed OH- gradient, DIDS-sensitive folate uptake was cis inhibited (greater than 90%) by reduced folate analogues: dihydrofolate (IC50 = 0.40 microM), folinic acid (IC50 = 0.50 microM), 5-methyltetrahydrofolate (IC50 = 0.53 microM), and (+)amethopterin (IC50 = 0.93 microM). In contrast, 10 microM (-)amethopterin had only a modest effect on folate uptake (18% inhibition) suggesting stereospecificity of the folate/OH- exchanger. The nonpteridine compounds which are transported by the folate carrier in L1210 leukemic cells (phthalate, thiamine pyrophosphate, and PO4(-3] did not inhibit jejunal folate uptake. Furthermore, folate uptake was not inhibited by SO4(-2) (4 mM) or oxalate (4 mM) thereby distinguishing this carrier from the previously described intestinal SO4(-2)/OH- and oxalate/Cl- exchangers. After BBM vesicles were loaded with 3H-folate, the initial velocity of 3H-folate efflux was stimulated by unlabeled folate in the efflux medium. The transstimulation of 3H-folate efflux by unlabeled folate was furosemide (or DIDS) inhibitable and temperature sensitive. Half-maximal stimulation of furosemide-sensitive 3H-folate efflux was observed with 0.25 +/- 0.05 microM unlabeled folate, a concentration similar to the Km for folate uptake. These data suggest that folate-stimulated 3H-folate efflux is mediated by the folate/OH- exchanger.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Toxicity of solubilized and colloidal amphotericin B formulations to human erythrocytes.

The toxicity of a number of solubilized or colloidal amphotericin B formulations to human erythrocytes has been studied in-vitro. All the solubilized formulations studied, using poloxamer F127 or L92, or sodium deoxycholate as solubilizing agents, showed similar toxicity, erythrocyte lysis being greater than 90% for amphotericin B concentrations between 4 to 8 micrograms mL-1. Emulsion formulations stabilized by poloxamers showed reduced toxicity, while those stabilized by egg lecithin showed less than 5% erythrocyte lysis up to an amphotericin B concentration of 200 micrograms mL-1. The mechanisms of the differential toxicity is considered to be due to the differences in the equilibrium concentration of free amphotericin B in the aqueous phase.

Adult↗
PubMed1985

The transmembrane pH gradient drives uphill folate transport in rabbit jejunum. Direct evidence for folate/hydroxyl exchange in brush border membrane vesicles.

In rabbit jejunal, but not ileal brush border membrane vesicles, an outwardly directed OH- gradient (pH 7.7 inside, pH 5.5 outside) markedly stimulated the initial velocity of folate (0.1 microM) uptake compared with uptake in the absence of a pH gradient. Under pH gradient conditions, folate was transiently accumulated at a concentration four times that found at equilibrium (over-shoot), implying uphill transport of the vitamin. Equilibrium folate uptake was inversely proportional to medium osmolality, suggesting uptake into an osmotically sensitive space. pH gradient-stimulated folate uptake was markedly reduced by inhibitors of anion exchange (4,4'-diisothiocyano-2,2'-disulfonic acid stilbene; 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid; furosemide), and was saturable (folate Km = 0.19 +/- 0.02 microM; Vmax = 12.8 +/- 0.4 pmol X mg protein-1 X min-1). Imposition of an inside-positive electrical potential did not stimulate folate uptake, suggesting that stimulation by a pH gradient was not due to an induced electrical potential. In contrast, an inwardly directed Na+ or K+ gradient did not stimulate folate uptake. These findings provide evidence for a carrier on the jejunal brush border membrane that mediates folate/OH- exchange (or H+/folate co-transport), and are consonant with the known presence of an outwardly directed OH- gradient in vivo (brush border acid microclimate), an acidic pH optimum for intestinal folate uptake, and the primary role of the jejunum in folate absorption.

Animals↗
PubMedDate not supplied

Stages of change and psychosocial correlates of fruit and vegetable consumption among rural African-American church members.

PURPOSE: This study examined the relationship between stages of change, other psychosocial factors, and fruit and vegetable (F&V) consumption among rural African-Americans participating in a 5 a Day study. DESIGN: The cross-sectional design assessed associations between F&V intake, stage of change, self-efficacy, beliefs, barriers, and social support. SETTING: Participants were surveyed by telephone. SUBJECTS: Subjects were 3557 adult church members (response rate, 79.1%), aged 18 and over from 10 North Carolina counties. MEASURES: A seven-item food frequency measured F&V intake. Stage of change was measured using four items; other psychosocial variables were measured using Likert scales. Chi-square tests and analysis of variance were used in statistical analyses. RESULTS: The majority of participants (65%) were in the preparation stage of change. Individuals in action/maintenance consumed an average of 6.5 daily F&V servings compared to 3.3 to 3.5 servings for those in precontemplation, contemplation, and preparation. Self-efficacy, social support, and belief about how many daily F&V servings are needed, were positively associated with stage. Barriers were most prevalent among precontemplators. CONCLUSIONS: The findings support the applicability of the stages-of-change model to dietary change among rural African-Americans. The relationship between stage, self-efficacy, social support, and barriers supports using a multicomponent intervention strategy.

Adult↗