ISSN:
0021-9541
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Transport of 3-O-methyl-(1-3H)-D-glucose (3-OMG) was studied in primary cell cultures of the R3230AC rat mammary adenocarcinoma. Fastest rates of carrier-mediated 3-OMG transport (vc) were temporally associated with fastest cell growth, as were the rates of 3H-labeled thymidine, uridine, and leucine incorporation into macromolecules. The decrease in vc for 3-OMG observed as cultured cells approached quiescence was due to a 4-fold decrease in Vmax with the Km remaining relatively constant (4-9mM). Provided adequate time was allowed for cells to adapt, (6-12hr), the vc for 3-OMG transport was found to be inversely related to the concentration of glucose in the medium. Within 6 hours after switching cells from standard growth medium (5mM glucose) to medium containing no glucose (5 mM fructose), a 2-fold increase in vc for 3-OMG transport was observed in both fast and slow growing cells. The glucose-starvation induced increase in 3-OMG transport was due to an increase in Vmax; the Km remained constant, and was not significantly influenced by the presence of serum (10%) or insulin (5 m̈g/ml) or by [5 mM] galactose, mannose, fructose, 2-deoxy-D-glucose, 3-OMG, or mannitol. Readdition of glucose (5 mM) to transport-activated cells (deprived of glucose for 9-11 hr) resulted in a rapid return of 3-OMG transport to basal levels. In the presence of cycloheximide (10 m̈g/ml) or actinomycin D (10 m̈g/ml), this glucose-induced decline in carrier function was largely blocked. In fast-growing cells, the addition of either of these inhibitors, in the presence or absence of glucose, resulted in an initial rise in the rates of 3-OMG transport, followed by a linear decrease. Compared to fast-growing cells, the cycloheximide-induced increase in 3-OMG transport was greater and longer sustained in slow-growing cells. Regardless of their growth rate, cell cultures preincubated in medium containing glucose and cycloheximide exhibited decreases in 3-OMG transport when transferred to medium containing fructose, with or without actinomycin D. Slow-growing cells preincubated in medium containing fructose and cycloheximide exhibited an increase in 3-OMG transport when switched to medium containing fructose, whereas similarly treated fast growing cell cultures displayed a slight decrease. These experiments suggest that the adaptive regulation of glucose transport in these mammary tumor cell cultures occurred at the transcriptional level and was influenced by the rates of cellular growth. A model in which a metabolite of glucose acts to enhance the synthesis or stabilization of a mRNA species specific for a putative carrier inactivator protein is proposed.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcp.1041020207
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