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G Li

Publications and source records attributed to G Li.

At least 1,045 records · Page 58Linked to original sources
PubMed1984

Induction of sugar uptake response to insulin by serum depletion in fusing L6 myoblasts.

The L6 muscle cell line is proposed as an excellent cell culture system for studying glucose transport and its regulation by serum and insulin throughout myogenesis. The rate of hexose uptake decreased after cell fusion. Fetal calf serum (5 h) stimulated hexose uptake, and serum deprivation depressed it. Both effects were prevented by cycloheximide. Insulin stimulated the uptake of either 2-deoxy-D-glucose or 3-O-methyl-D-glucose provided that the basal rate was previously depressed by serum deprivation. The response to the hormone was significant only after the onset of cell fusion. Stimulation of transport was observed within the first 10 min after insulin administration and was insensitive to cycloheximide. Half-maximal stimulation of uptake was obtained with 5 X 10(-8) M insulin in 1% albumin solutions. Basal and insulin-stimulated uptake showed equal sensitivity to cytochalasin B. However, they differed in their sensitivity to extracellular Ca2+: basal transport was depressed, whereas insulin-stimulated transport was further enhanced in Ca2+-free media. Advantages of the cell culture system are discussed.

3-O-Methylglucose↗
PubMed1984

Role of calcium ions in insulin action on hexose transport in L6 muscle cells.

It has been proposed that Ca2+ ions mediate the stimulation by insulin of glucose uptake in muscle (Clausen, T., Cell Calcium 1:311-325, 1980). However, absolute measurements of the concentration of cytosolic free Ca2+, [Ca2+]i, during the course of insulin action have not been made. The stimulation of hexose uptake by insulin was studied in an in vitro model system of muscle cells, the L6 cell line. The following evidence suggests that Ca2+ ions are not likely to fulfill the purported role. 1) Insulin in Ca2+-free media induced stimulation of 2-deoxy-D-glucose uptake. 2) Elevation of [Ca2+]i with the ionophore A23187 did not enhance hexose uptake. 3) Insulin action was not diminished when the hormone was added to Ca2+-depleted cells in Ca2+-free media with A23187. 4) Hexose uptake was not affected by a number of agents thought to modify [Ca2+]i including epinephrine, caffeine, 2,4-dinitrophenol, hyperosmolar mannitol, salicylate, vanadate, veratrine, and trypsin. 5) Direct determinations of [Ca2+]i by fluorescence of the novel indicator Quin-2 did not show differences between basal and insulin-stimulated cells; under identical conditions hexose uptake was stimulated by the hormone. 6) Chelation of [Ca2+]i with Quin-2 in Ca2+-free media did not affect the response to insulin. 7) Low concentrations of trypsin (7.5 micrograms/ml) elevated [Ca2+]i but did not increase the rate of hexose uptake.

Aminoquinolines↗
PubMed1983

Role of calcium in serum-stimulation of hexose transport in muscle cells.

Serum stimulates glucose uptake into several cells in culture. In intact muscle, an increase in cytosolic free Ca2+ has been proposed to mediate the activation of glucose uptake by hormones and other stimuli [Cell Calcium (1980) 1, 311-325]. We report that hexose (2-deoxy-D-glucose) uptake into L6 muscle cells in culture is enhanced several-fold by fetal calf serum. The increase in uptake is due to stimulation of transmembrane transport, since serum also stimulated uptake of the non-metabolizable hexose 3-O-methyl-D-glucose. The role of Ca2+ in this stimulation was assessed: (i) stimulation of transport by serum was independent of the presence of extracellular Ca2+ during the incubation with serum; (ii) the intracellular levels of free Ca2+, measured by the fluorescence of the novel Ca-indicator quin-2, were identical in serum-stimulated and control cells. It is concluded that hexose transport can increase in muscle cells without concomitant changes in cytoplasmic free Ca2+.

Animals↗
PubMed1983

The results of radiation therapy in advanced carcinoma of the lung in the Beijing region of China.

From 1958 to 1973, 682 patients with lung cancer were treated by radiation therapy in the Cancer Institute, Chinese Academy of Medical Sciences, Beijing, China. The clinical presentation, sex, age, histology and stage and palliative effects of radiation therapy were reported. The 1-, 3- and 5-year survival rates were 40.62, 8.94 and 3.81%, respectively. The prognostic factors such as staging, histology, combination with chemotherapy and response of tumours are discussed. The causes of failure are also analysed. It is suggested that improving the local control rate of squamous cell carcinoma would increase the survival rate.

Adenocarcinoma↗
PubMed1983

Insulin binding to differentiating muscle cells in culture.

Saturable binding of 125I-labelled insulin was detected on L6 myoblasts grown in monolayers. Binding was proportional to the number of cells and was pH sensitive, decreasing above pH 7.0. Binding also decreased with increasing temperature in the range 22-37 degrees C. Binding of insulin over a range of hormone concentrations (10(-10)-10(-6) M) was analyzed by Scatchard plots. The data are compatible with the coexistence of two components with Kd of 3 and 190 nM. The number of both types of binding sites increased with cell differentiation (upon alignment and cell fusion), when expressed either per unit protein, DNA, or surface membrane cholesterol. On the other hand, their association constants did not vary. Binding of insulin to a nonfusing mutant of L6 cells resembled binding to the parent myoblasts before alignment.

Animals↗
PubMed1982

Hexose transport in L6 muscle cells. Kinetic properties and the number of [3H]cytochalasin B binding sites.

(1) Myoblasts in culture (L6 cell line) were used as an in vitro model system, to study the kinetic and pharmacological properties of hexose transport in skeletal muscle tissue. (2) Uptake of 2-deoxy-D-[3H]glucose into L6 cells grown in monolayer culture was judged rate limiting since: (2) The time course of sugar uptake extrapolated to zero, (b) a parallel inhibition of hexose uptake and phosphorylation was caused by cytochalasin B, and (c) very little backflow of the hexose was detected. (3) Uptake of 2-deoxy-D-[3H]glucose by cells in monolayers was linear for at least 20 min and it was stimulated by countertransport. The Kt value was 0.83 mM. Cytochalasin B inhibited uptake non-competitively, and half maximal inhibition was achieved at 0.3 microM. Cytochalasin E (up to 5 microM) did not affect 2-deoxy-D-[3H]glucose uptake. (4) L6 myoblasts, detached by trypsinization, retained the hexose transport activity. Kt in detached cells was 0.96 mM. V was 3.2 nmol/min per mg protein, and half maximal inhibition was observed with 0.25 microM cytochalasin B. (5) [3H]Cytochalasin B binding to detached cells showed saturable and non-saturable components. The former could be further separated into cytochalasin E-sensitive binding (probably associated to cytoskeletal proteins) and cytochalasin E-insensitive binding, a fraction of which was inhibited by D-glucose. The D-glucose sensitive sites amount to 16.3 pmol/mg protein, and showed a Kd of 0.49 microM, which is in close agreement with the Ki of cytochalasin B inhibition of hexose uptake. These sites probably are equivalent to the hexose carrier molecules, and are present at a density of 6.8 . 10(6) sites/cell.

3-O-Methylglucose↗