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Biomedical subjects

A K Sen

Publications and source records attributed to A K Sen.

At least 73 records · Page 4Linked to original sources
PubMed1986

Immunochemical properties of the lipopolysaccharide O-antigen of Vibrio cholerae O1 in relation to its chemical structure.

D-Glucuronic acid and D-glucosamine have an immunodominant role in the lipopolysaccharide (LPS) O-antigen of both the Ogawa and the Inaba subtypes of Vibrio cholerae O1. This was evident from the pronounced inhibitory effect on the LPS precipitin reaction demonstrated by these monosaccharides and by oligosaccharides containing either of them which were isolated from LPS hydrolysate. There was a considerable decrease in the antibody-combining capacity of chemically modified LPS in which the carboxyl group of the glucuronic acid had been reduced. Similarly, on deamination, the O-specific polysaccharide fraction of the LPS molecule from both subtypes completely lost the ability to precipitate the LPS antibody.

Antigens, Bacterial↗
PubMed1986

Digitalis-like biological activity in rat cerebellum.

The cytosolic fraction of rat cerebellum possesses a factor(s) which is capable of inhibiting synaptosomal Na,K-ATPase activity, competing with [3H]ouabain binding to rat brain synaptosomes, and inducing positive inotropy in guinea pig atrial strips. These results demonstrate the existence of a ouabain-like principle in rat cerebella. The inhibitory activity of the factor was found to be partially thermolabile and diminished by a proteolytic agent, and the activity could be augmented by increasing concentrations of Mg2+, suggesting a regulatory mechanism for the endogenous digitalis-like principle.

Animals↗
PubMed1985

The presence of a heat-stable cytosolic factor in rat submandibular gland which activates Na+,K+-ATPase.

A low molecular weight substance is present in the soluble fraction of the rat submandibular gland which activates Na+,K+-ATPase. Varying amounts of cytosolic protein from rat submandibular gland were added to a heavy microsomal preparation of the same tissue. A dose-dependent activation of the Na+,K+-ATPase was observed, with a peak activation of approximately 82% occurring when 9.0 micrograms/mL of cytosolic protein was included in the assay. The activating factor is heat stable and soluble following heat treatment. The factor elutes at a molecular mass of 600 daltons as determined by molecular sieve column chromatography. Ultraviolet-visible scanning of the elute material results in an absorbance at 210 nm, which is characteristic of a low molecular weight peptide.

Animals↗
PubMed1984

Release of 86Rb from rat submandibular gland slices: relation to sodium pump activity.

Slices of rat submandibular gland were preloaded with 86Rb, an isotope that can substitute for K+ in the K+ release process. The efflux of 86Rb was monitored in a superfusion apparatus that efficiently removed the 86Rb as it exited from the tissue slices. Carbachol and the calcium ionophore A23187 activated a calcium-dependent increase in 86Rb efflux. Dibutyryl cGMP had no detectable effect on 86Rb efflux in contrast to its activation of ouabain-sensitive uptake of 86Rb observed in an earlier study. The stimulated release of 86Rb was not dependent on the presence of either sodium or chloride ions. When 86Rb efflux was stimulated by carbachol, the efflux rate returned toward the basal rate after a few minutes of exposure to carbachol in the medium. If ouabain was then introduced into the superfusate, a large increase in efflux was stimulated. In the absence of carbachol, only a small increase in 86Rb efflux was stimulated by ouabain. The effect of ouabain indicates that there was a substantial recycling of 86Rb between the release and uptake processes in the extracellular space of the tissue slice. The significance of this observation is discussed.

Animals↗
PubMed1983

Regulation of canine heart sarcolemmal Ca2+-pumping ATPase by cyclic GMP.

Cyclic nucleotide modulation of the sarcoplasmic reticulum calcium pump has been recognized for some time. Little is known, however, of cyclic nucleotide effects on the sarcolemmal Ca2+-pump. In sarcolemmal vesicles prepared from ventricular muscle by a recent technique (Jones, L.R., Maddock, S.W. and Besch, H.R. (1980) J. Biol. Chem. 255, 9971-9980) we have demonstrated via Millipore filtration that 10(-8) M and 10(-9) M cyclic GMP depressed the rate of ATP- and Mg2+-dependent 45Ca2+ uptake by 34% and 52%, respectively. Only at millimolar levels did cyclic AMP have any effect and the respective 5'-nucleotides had no effect at all. Parallel measurement of the associated (Ca2+ + Mg2+)-ATPase in the presence of either cyclic or 5'-nucleotides, however, revealed no concomitant depression in ATP hydrolysis. In another series of experiments, the cyclic GMP effect on 45Ca2+ uptake was associated with a significant decrease in the pump Vmax, and at the most effective concentration of cyclic GMP increased the apparent Km for Ca2+. These results suggest that cyclic GMP may depress ventricular Ca2+ efflux by decreasing the enzyme turnover and to a limited extent, decreasing pump affinity for Ca2+. This supports a hypothesis whereby cyclic GMP might modulate both local biochemical and electrophysiological events by an effect on a discrete, regional pool of intracellular Ca2+.

Adenosine Triphosphate↗
PubMed1983

Correlation between reaction time and intelligence in psychometrically similar groups in America and India.

The relationship between psychometrically tested reasoning ability, or general intelligence (Raven's Progressive Matrices), short-term memory (forward and backward digit span), and measures of reaction time (RT), including visual and auditory simple RT and four degrees of choice RT, was investigated in groups of unskilled workers, mostly of below average, borderline, or retarded mental ability, selected in the United States and in India. Both groups showed parallel phenomena with respect to the relative difficulty of the various RT tests, their factor structure, and their theoretically expected correlations with psychometric intelligence, although the correlations were lower (and generally nonsignificant) in the Indian group, most likely because of this group's greater restriction in range of ability. The findings, overall, are consistent with other recent studies of RT and intelligence, which indicate that our standard IQ tests reflect basic cognitive processes, particularly speed of information processing, involved in individual differences in intellectual ability, and not merely differences in specific acquired knowledge, skills, or cultural background.

Adolescent↗
PubMed1983

Cholinergic stimulation of ouabain-sensitive respiration in rat submandibular gland.

Oxygen consumption of slices of rat submandibular gland was monitored with an oxygen electrode method. Carbachol stimulated an immediate increase in tissue respiration that was inhibitable by ouabain. The stimulation required the presence of calcium in the incubation medium and was blocked by atropine. The calcium ionophore A23187 also stimulated ouabain-sensitive oxygen consumption in the tissue slices. The results show that the mechanism using the extra energy during cholinergic stimulation is the sodium pump. Amiloride at a 1, 10, or 100 microM concentration had no effect on stimulation of ouabain-sensitive respiration by carbachol. Since amiloride, which is known to block the sodium reabsorption process in the ductal segment, has no effect on the stimulation, the increased sodium pump activity is probably located in the acinar region and is associated with the primary fluid secretion process.

Amiloride↗
PubMed1982

Regulation of rat brain (Na+ +K+)-ATPase activity by cyclic AMP.

The interaction between the (Na+ +K+)-ATPase and the adenylate cyclase enzyme systems was examined. Cyclic AMP, but not 5'-AMP, cyclic GMP or 5'-GMP, could inhibit the (Na+ +K+)-ATPase enzyme present in crude rat brain plasma membranes. On the other hand, the cyclic AMP inhibition could not be observed with purified preparations of (Na+ +K+)-ATPase enzyme. Rat brain synaptosomal membranes were prepared and treated with either NaCl or cyclic AMP plus NaCl as described by Corbin, J., Sugden, P., Lincoln, T. and Keely, S. ((1977) J. Biol. Chem. 252, 3854-3861). This resulted in the dissociation and removal of the catalytic subunit of a membrane-bound cyclic AMP-dependent protein kinase. The decrease in cyclic AMP-dependent protein kinase activity was accompanied by an increase in (Na+ +K+)-ATPase activity. Exposure of synaptosomal membranes containing the cyclic AMP-dependent protein kinase holoenzyme to a specific cyclic AMP-dependent protein kinase inhibitor resulted in an increase in (Na+ +K+)-ATPase enzyme activity. Synaptosomal membranes lacking the catalytic subunit of the cyclic-AMP-dependent protein kinase did not show this effect. Reconstitution of the solubilized membrane-bound cyclic AMP-dependent protein kinase, in the presence of a neuronal membrane substrate protein for the activated protein kinase, with a purified preparation of (Na+ +K+)-ATPase, resulted in a decrease in overall (Na+ +K+)-ATPase activity in the presence of cyclic AMP. Reconstitution of the protein kinase alone or the substrate protein alone, with the (Na+ +K+)-ATPase has no effect on (Na+ +K+)-ATPase activity in the absence or presence of cyclic AMP. Preliminary experiments indicate that, when the activated protein kinase and the substrate protein were reconstituted with the (Na+ +K+)-ATPase enzyme, there appeared to be a decrease in the Na+-dependent phosphorylation of the Na+-ATPase enzyme, while the K+-dependent dephosphorylation of the (Na+ +K+)-ATPase was unaffected.

Adenylyl Cyclases↗
PubMed1981

Role of cyclic GMP in cholinergic activation of Na-K pump in duck salt gland.

Na-K-ATPase will hydrolyze an alternate substrate, p-nitrophenylphosphate (pNPP). The hydrolysis is ouabain sensitive and occurs at an external site on the cell membrane, thereby allowing measurement of Na-K-ATPase activity in the intact cell. pNPP hydrolysis was monitored in salt gland slices incubated in a bicarbonate-buffered Ringer solution. Methacholine-stimulated pNPP hydrolysis was inhibited by either atropine or ouabain. The hydrolysis was also dependent on the presence of calcium and sodium in the Ringer solution. cGMP stimulated ouabain-sensitive pNPP hydrolysis at concentrations from 10(-8) M to 10(-4) M with an optimum at 10(-5) M. cAMP did not produce a significant activation of pNPP hydrolysis. The effect of cGMP ws not dependent on either sodium or calcium in the Ringer solution and was not inhibited by atropine. Hydrolysis of pNPP promoted by either methacholine or cGMP occurred under conditions where no net influx of Na+ into the cells could occur. Sodium-pump activation during cholinergic stimulation, therefore, does not depend on an elevation of cell sodium but must occur by another mechanism. cGMP appears to play a direct role in that mechanism.

4-Nitrophenylphosphatase↗
PubMed1980

Studies on the partial structure of the O-antigen of Vibrio cholera, Inaba 569 B.

Five oligosaccharides were isolated in pure state from the lipopolysaccharide of Vibrio cholera, Inaba 569 B, the their structures were elucidated. More-detailed information regarding the partial structure of the lipopolysaccharide, containing glucose, mannose, glucuronic acid, 2-amino-2-deoxyglucose, D-glycero-L-mannoheptose, and D-glycero-L-gluco-heptose, was obtained through Smith degradation, chromium trioxide oxidation, and graded hydrolysis studies of the lipopolysaccharide and its derived products.

Antigens, Surface↗
PubMed1980

Activation of ouabain-sensitive p-nitrophenylphosphatase by carbachol and cGMP in rat submandibular gland.

Na+,K+-ATPase activity was monitored by measuring ouabain-sensitive K+-dependent p-nitrophenylphosphatase (p-NPPase) activity in rat submandibular gland slices. Carbachol (carbamylcholine chloride) stimulated the p-NPPase activity in the presence of calcium but not in its absence. Carbachol activation of the enzyme was totally ouabain sensitive and could be blocked by atropine. A minimal requirement of sodium ion extracellularly was required for this carbachol stimulation. cGMP and its dibutyryl analogue was also effective in stimulating the enzyme activity, whereas, cAMP was ineffective. Calcium, however, was not required for cGMP activation of the p-NPPase activity. The result indicates that calcium is the second messenger and cGMP is the tertiary connection between cholinergic stimulation and Na+,K+-ATPase activation in these glands. Activation of Na+,K+-ATPase is postulated to be responsible for primary fluid formation.

4-Nitrophenylphosphatase↗
PubMed1979

Structural investigations of the lipopolysaccharide isolated from Vibrio cholera, Inaba 569 B.

On hydrolysis, the purified lipopolysaccharide (LPS) isolated from Vibrio cholera, Inaba 569 B, yielded glucose, mannose, a heptose behaving like D-glycero-L-manno-heptose and one behaving like D-glycero-L-gluco-heptose, 2-amino-2-deoxyglucose, and glucuronic acid in the molar ratios of approximately 9:4:5:1:2:5. Studies on the LPS, the polysaccharide (PS), and carboxyl-reduced LPS showed that the PS has a branched structure, with (1 leads to 2)-linked mannopyranosyl and a heptopyranosyl, and (1 leads to 4)-linked glucopyranosyluronic and 2-amino-2-deoxyglucopyranosyl residues in the interior part of the molecule, and glucopyranosyl and heptopyranosyl residues as nonreducing end-groups.

Carbohydrates↗