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Biomedical subjects

S Majumdar

Publications and source records attributed to S Majumdar.

At least 325 records · Page 18Linked to original sources
PubMed1986

Spontaneous cholesterol movement between lipid vesicles and monkey small intestinal brush border membrane.

[14C]Cholesterol movement between egg phosphatidylcholine-cholesterol lipid vesicles and vesicles prepared from monkey small intestinal brush border membrane (BBMV) was studied in physiological buffer at 37 degrees C. The rate of cholesterol transfer from sonicated unilamellar vesicles (ULV) to BBMV follows apparently first-order kinetics. Intermembrane cholesterol movement was strikingly similar in both the directions. However, from BBMV to ULV, the transfer rate was three times faster than that of ULV to brush border membrane (BBM). Similarity in the rate constant was observed when cholesterol transfer was studied using either large multilamellar lipid vesicles or ULV as the donor and BBMV as the acceptor membrane. Rate constant was also the same when the acceptor membrane used was either intact BBMV or ULV prepared from BBM lipids. The rate of transfer of label was not affected even when the acceptor vesicle concentration was increased over fivefold, indicating the first-order nature of the reaction. Transfer of cholesterol from ULV to BBMV was accelerated by the presence of acetone, dimethyl sulfoxide (DMSO), deoxycholate, and papain. Partially purified nonspecific lipid-exchange protein increased the rate of cholesterol transfer by about threefold. Reduction in BBM cholesterol and phospholipid content was noted by DMSO, acetone, and deoxycholate, while papain caused a small depletion of membrane protein. Cholesterol transfer is temperature dependent with an activation energy of 31 kJ X mol-1, which is almost identical in the presence or absence of nonspecific lipid-exchange protein. The molecular mechanism of intermembrane cholesterol movement is discussed in view of the kinetic data obtained.

Animals↗
PubMed1986

Selective action of mycobacillin on the cellular permeability of Aspergillus niger.

Cells of Aspergillus niger normally release not all but of some specific cell constituents viz., lysine, proline, ATP, Pi, Na+, K+ and Ca2+ in the absence of mycobacillin. Mycobacillin enhances the release of these materials without causing lysis. The time and concentration of mycobacillin for optimum release depends on the nature of the materials involved.

Adenosine Triphosphate↗
PubMed1986

Small vessel disease in vasectomized diabetic monkeys: light microscopic study.

The following four groups of rhesus monkeys were studied for small vessel pathology of the heart, kidney and retina: sham-vasectomized, vasectomized, sham-vasectomized diabetic and vasectomized diabetic. A significant increase was observed in the frequency of pathological changes in small vessels (less than 60 micron diameter), of the heart muscle of nondiabetic vasectomized monkeys, and in sham-vasectomized and vasectomized diabetic monkeys. Further, the thickness of the glomerular capillary basement membrane was also significantly increased in the three experimental groups. In vasectomized diabetic monkeys, the vascular lesions were much greater than in the other two groups. Moreover, in this group one animal had a microaneurysm of a retinal vessel and another had distortion of retinal veins. The monkeys subjected to vasectomy or diabetes alone did not develop these changes. However, the ratio of mural to endothelial cells in retinal vessels was markedly altered in vasectomized and nonvasectomized diabetic monkeys.

Animals↗
PubMed1985

The effect of medroxyprogesterone acetate on the hepatic drug-metabolizing enzymes in normal and protein-deficient female rats.

Effect of depot medroxyprogesterone acetate on the hepatic drug-metabolizing enzymes was studied in female protein-deficient and normal pair-fed rats. Treatment with this drug did not cause any change in organ weight, microsomal protein, and soluble protein yield per gram of tissue in both groups. MPA administration resulted in significant increases in the content of cytochrome P-450 and b5, and activities of benzo[a]pyrene hydroxylase, UDP-glucuronosyltransferase, and NADPH-Cyt c reductase in both pair-fed control and protein-deficient rats. However, the content of glutathione and activity of glutathione-S-transferase were not affected appreciably. The present study suggests that MPA treatment induces drug-metabolizing enzymes in liver to almost the same extent in both protein-deficient and normal pair-fed rats.

Animals↗
PubMed1985

Inhibition of D-glucose uptake by isatin in rat intestine: effect of harmaline and various sulfhydryl reagents.

The effect of isatin (indole-2,3-dione) on D-glucose uptake has been studied in rat intestine. Isatin at 6 mM concentration significantly inhibited both the sugar uptake and transmural (mucosal to serosal side) transport in the intestine. The suppression of glucose uptake by isatin was irreversible. Similar to the action of various SH-group-reacting agents, isatin inhibited the sugar uptake, presumably by binding to membrane sulfhydryl groups through a covalent linkage. Isatin-induced reduction in glucose uptake was unaffected by pH (between 5.5 and 8.4) and by DTT addition to incubation medium. Inhibition of sugar uptake by isatin and harmaline was additive in nature; this suggested that these compounds interact at different sites on the microvillus membrane surface.

Alkaloids↗
PubMed1985

Aggravation of experimental atherosclerosis in vasectomized, cholesterol-fed rabbits.

Rabbits were fed a stock or atherogenic diet for a period of fourteen months. Half of each group of rabbits was bilaterally vasectomized while the other half underwent sham vasectomy. The level of plasma cholesterol was significantly elevated following vasectomy in stock diet-fed rabbits. Atherogenic diet feeding caused marked elevation of plasma cholesterol in both vasectomized as well as sham-vasectomized animals. At the termination of the experiments, aortic cholesterol in stock diet-fed vasectomized rabbits remained unchanged, but this was increased in both vasectomized and sham-vasectomized atherogenic diet-fed animals. Aortic sudanophilia, atherosclerotic plaque size and coronary atherosclerosis index were significantly increased in vasectomized atherogenic diet-fed rabbits as compared to their controls. In stock diet-fed vasectomized rabbits no macroscopic or microscopic lesions were seen even in the presence of mild hypercholesterolaemia.

Animals↗
PubMed1985

Derepression of sporulation and synthesis of mycobacillin and dipicolinic acid by guanosine 3':5'-cyclic monophosphate under conditions of glucose repression in Bacillus subtilis.

Dibutyryl cyclic GMP, but not dibutyryl cyclic AMP, derepresses sporulation and synthesis of mycobacillin and dipicolinic acid under conditions of glucose repression in Bacillus subtilis strain B34. Neither of these compounds appears to affect sporulation and synthesis of mycobacillin and dipicolinic acid in this strain under normal physiological conditions. Mutants insensitive to glucose repression were indifferent to the addition of either of the nucleotides both in the presence and in the absence of glucose. A role for dibutyryl cyclic GMP in annulling the repressing effect of glucose on sporulation and on synthesis of mycobacillin and dipicolinic acid is thus indicated.

Antifungal Agents↗
PubMed1985

Effect of changes in the osmolarity of the growth medium on Vibrio cholerae cells.

The rate and extent of lysis of Vibrio cholerae cells under nongrowing conditions were dependent on the osmolarity of the growth medium. Gross alterations in cellular morphology were observed when V. cholerae cells were grown in media of high and low osmolarity. The rate of lysis of V. cholerae cells under nongrowing conditions increased after treatment with chloramphenicol. Chloramphenicol-treated V. cholerae 569B cells showed formation of sphaeroplast-like bodies in medium of high osmolarity, but not in low osmolarity. Changes in the osmolarity of the growth medium also regulated the expression of the outer membrane proteins. This regulation was abolished if V. cholerae cells were grown in Pi-depleted medium. Analysis of the lytic behavior and composition of outer membrane proteins of an osmotically fragile mutant strain revealed a similar dependence on the osmolarity of the growth medium.

Cell Membrane↗
PubMed1985

Effect of short-term and long-term treatment with a steroidal oral contraceptive on the intestinal absorption of nutrients in vitro in female rats.

The effect of steroidal oral contraceptive (SOC), comprising megestrol acetate (5 mg/kg body weight) plus ethinyl estradiol (0.05 mg/kg body weight), administered daily by stomach tube for 5, 15, 30 and 90 days, on the intestinal uptake of nutrients such as glucose, amino acids and calcium has been investigated in vitro in female rats. The administration of SOC for 5 days did not affect the uptake of nutrients, but treatment for 15, 30 and 90 days led to a progressive and significant increase in the uptake of glucose and amino acids. The calcium uptake was increased in the groups treated for 5 and 15 days, but decreased after 30 and 90 days of treatment. Kinetic studies done on glucose uptake indicated that the steroid contraceptive might be inducing the transport carrier protein of this nutrient, as elevation in Vmax was observed in the group treated for 30 days. There was no change in brush border membrane phospholipid and cholesterol contents after 30 and 90 days of treatment, but a significant increase in phospholipid after 5 and 15 days of treatment was observed. This study suggests that SOC treatment significantly altered the intestinal absorptive functions and the effect appears to be on the carrier-mediated transport of glucose.

Amino Acids↗
PubMed1985

UV-repair and mutagenesis in Azotobacter vinelandii. I. Repair of UV-induced damages.

UV-irradiated Azotobacter vinelandii OP cells were found to be sensitive to dark repair-inhibitors, like caffeine and acriflavine. Sensitivity to both the inhibitors started to decrease at a fast rate immediately following UV-irradiation, when incubated in Burk's broth in dark. Total insensitivity to caffeine was attained at a time that was approximately double the time of the corresponding ribonucleic acid synthesis-inhibition and less than one generation time of the unirradiated cells. Nearly at the same time the rate of loss of sensitivity to acriflavine became much slower and total insensitivity to acriflavine occurred after relatively prolonged incubation. The protein synthesis inhibitor, streptomycin, reduced UV-survival, but after a time lag. The organism did not show liquid holding recovery and its UV-survival was not affected by components of complex medium. It is proposed that A. vinelandii OP possesses at least two dark-repair pathways: pre replication (acts immediately after UV exposure and is faster) and post replication (delayed and slower) repair. The first one is inhibited by caffeine and acriflavine and the second by acriflavine and streptomycin. The latter therefore requires de novo protein synthesis after UV-irradiation and may be inducible.

Acriflavine↗