This review deals with the cellular mechanisms that transport milk constituents or the precursors of milk constituents into, out of, and across the mammary secretory cell. The various milk constituents are secreted by different intracellular routes, and these are outlined, including the paracellular pathway between interstitial fluid and milk that is present in some physiological states and in some species throughout lactation. Also considered are the in vivo and in vitro methods used to study mammary transport and secretory mechanisms. The main part of the review addresses the mechanisms responsible for uptake across the basolateral cell membrane and, in some cases, for transport into the Golgi apparatus and for movement across the apical membrane of sodium, potassium, chloride, water, phosphate, calcium, citrate, iodide, choline, carnitine, glucose, amino acids and peptides, and fatty acids. Recent work on the control of these processes, by volume-sensitive mechanisms for example, is emphasized. The review points out where future work is needed to gain an overall view of milk secretion, for example, in marsupials where milk composition changes markedly during development of the young, and particularly on the intracellular coordination of the transport processes that result in the production of milk of relatively constant composition at a particular stage of lactation in both placental and marsupial mammals.
Objective: To evaluate longitudinally the effectiveness of a cooking programme on self-reported confidence about cooking skills and food consumption patterns in parents of young children. Design: An evaluation of cooking programmes delivered by National Health Service (NHS) community food workers using a single group pre-test/post-test repeated measures design. A shortened version of a validated questionnaire at baseline, post intervention and 1-year follow-up determined confidence in cooking using basic ingredients, following a simple recipe, tasting new foods, preparing and cooking new foods on consumption of ready meals, vegetables and fruit. Setting: Deprived communities in Ayrshire and Arran, Scotland. Subjects: Parents of nursery age children, 97 % were female and ,45 years old. Results: One hundred and two participants had completed baseline and postintervention questionnaires. Forty-four participants contacted by telephone completed a follow-up questionnaire. In participants who completed all questionnaires (n 44), median confidence in four aspects of cooking increased significantly from baseline to post intervention (P , 0?001) but was retained at 1-year follow-up only for following a simple recipe and preparing and cooking new foods. Improved food consumption patterns were reported from baseline to post intervention (ready-meal consumption reduced from 2-4 times/week to 1 time/week, P , 0?001; vegetable consumption increased from 5-6 times/week to 1 time/d, P , 0?001; fruit consumption increased from 5-6 times/week to 1 time/d, P , 0?001) and remained at 1-year follow-up. Conclusions: The cooking programmes appeared to improve cooking confidence and food consumption patterns in the target group and some of these changes were retained after 1 year.
The activity and expression of indoleamine 2,3-dioxygenase together with L-tryptophan transport has been examined in cultured human breast cancer cells. MDA-MB-231 but not MCF-7 cells expressed mRNA for indoleamine 2,3-dioxygenase. Kynurenine production by MDA-MB-231 cells, which was taken as a measure of enzyme activity, was markedly stimulated by interferon-gamma (1000 units/ml). Accordingly, L-tryptophan utilization by MDA-MB-231 cells was enhanced by interferon-gamma. 1-Methyl-DL-tryptophan (1 mM) inhibited interferon-gamma induced kynurenine production by MBA-MB-231 cells. Kynurenine production by MCF-7 cells remained at basal levels when cultured in the presence of interferon-gamma. L-Tryptophan transport into MDA-MB-231 cells was via a Na(+)-independent, BCH-sensitive pathway. It appears that system L (LAT1/CD98) may be the only pathway for l-tryptophan transport into these cells. 1-Methyl-D,L-tryptophan trans-stimulated l-tryptophan efflux from MDA-MB-231 cells and thus appears to be a transported substrate of system L. The results suggest that system L plays an important role in providing indoleamine-2,3-dioxygenase with its main substrate, L-tryptophan, and suggest a mechanism by which estrogen receptor-negative breast cancer cells may evade the attention of the immune system.
The transport of L-leucine by two human breast cancer cell lines has been examined. L-leucine uptake by MDA-MB-231 and MCF-7 cells was via a BCH-sensitive, Na+ -independent pathway. L-leucine uptake by both cell lines was inhibited by L-alanine, D-leucine and to a lesser extent by L-lysine but not by L-proline. Estrogen (17beta-estradiol) stimulated L-leucine uptake by MCF-7 but not by MDA-MB-231 cells. L-leucine efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH in a dose-dependent fashion. The effect of external BCH on L-leucine efflux from both cell types was almost abolished by reducing the temperature from 37 to 4 degrees C. There was, however, a significant efflux of L-leucine under zero-trans conditions which was also temperature-sensitive. L-glutamine, L-leucine, D-leucine, L-alanine, AIB and L-lysine all trans-stimulated L-leucine release from MDA-MB-231 and MCF-7 cells. In contrast, D-alanine and L-proline had little or no effect. The anti-cancer agent melphalan inhibited L-leucine uptake by MDA-MB-231 cells but had no effect on L-leucine efflux. Quantitative real-time PCR revealed that LAT1 mRNA was approximately 200 times more abundant than LAT2 mRNA in MCF-7 cells and confirmed that MDA-MB-231 cells express LAT1 but not LAT2 mRNA. LAT1 mRNA levels were higher in MCF-7 cells than in MDA-MB-231 cells. Furthermore, LAT1 mRNA was more abundant than CD98hc mRNA in both MDA-MB-231 and MCF-7 cells. The results suggest that system L is the major transporter for L-leucine in both MDA-MB-231 and MCF-7 cells. It is possible that LAT1 may be the major molecular correlate of system L in both cell types. However, not all of the properties of system L reflected those of LAT1/LAT2/CD98hc.
SUMMARYWe have examined the effect of a hyposmotic shock, and thus cell swelling, upon the efflux of amino acids, SO42-and 1-from lactating mammary tissue. A hyposmotic challenge increased the efflux of taurine and glycine via a 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS)-sensitive pathway. It appears that these amino acids do not exit via an anion-exchange mechanism following cell swelling because sulphate efflux, which uses a DIDS-sensitive exchange mechanism, was unaffected. The hyposmotic-induced efflux of taurine was not dependent upon the Na+ gradient and was not influenced by the nature of the anion in the incubation medium. In addition, taurine efflux was stimulated by incubating mammary tissue in an isosmotic medium that contained urea, suggesting that cell swelling is the stimulating factor rather than a decrease in osmolality per se. The results suggest that mammary tissue uses taurine and glycine as a means of regulating cell volume following swelling. In contrast, the efflux of glutamic acid, alanine and ac-aminoisobutyric acid was unaffected by a hyposmotic challenge.Similarly, the efflux of 1-was unaffected by such a challenge. The results suggest that volumeactivated amino acid transport in lactating rat mammary tissue is distinct from volume-regulated anion channels.
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