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At least 1,063 records · Page 59Linked to original sources
PubMed1984

Sensitivity of guinea-pig hippocampal granule cell field potentials to hexoses in vitro: an effect on cell excitability?

Evoked granule cell field potentials, and levels of tissue metabolites, in superfused guinea-pig hippocampal slices have been studied in the presence of low glucose and an alternative glycolytic substrate (D-fructose). The effects of glucose analogues (5-thio-D-glucose, 2-deoxy-D-glucose or 3-O-methyl-D-glucose) in the presence of glucose were also tested. Concentrations of glucose or fructose in excess of 2 mM and 10 mM respectively were required to maintain normal evoked activity. 5-Thioglucose (15 mM) in the presence of 5 mM-glucose decreased the amplitude of the population spike by 60% with little effect on population excitatory post-synaptic potential (e.p.s.p.). Tissue levels of phosphocreatine and ATP were essentially unchanged under all conditions tested, with the exception of 10 mM-fructose. The decrease in rates of lactate efflux from superfused tissue during and after superfusion with 3-O-methylglucose, 2-deoxyglucose or 5-thioglucose was found to be positively correlated with the extent of attenuation of field potentials. Analysis of the relationship between population spike amplitude and rates of rise of e.p.s.p., under conditions where field potentials were attenuated, showed that the population spike was always more sensitive to metabolic perturbation than was the e.p.s.p., thus indicating an effect on cell excitability. It is suggested that some aspect of non-oxidative glucose metabolism is important in maintaining this granule cell excitability.

Action Potentials↗
PubMed1983

Influence of lectins, hexoses, and neuraminidase on the association of purified elementary bodies of Chlamydia trachomatis UW-31 with HeLa cells.

Using highly purified elementary bodies of Chlamydia trachomatis UW-31 (serotype K), we found that HeLa 229 monolayer cultures bound more 32P-labeled chlamydiae after pretreatment with the lectin wheat germ agglutinin. The lectin, on the other hand, inhibited competitively when chlamydial association was assayed in the presence of polycations. The two effects of wheat germ agglutinin were abolished when N-acetylneuraminic acid (NeuNAc)- or N-acetylglucosamine (GlcNAc)-preincubated wheat germ agglutinin was used. Brief exposure of HeLa cells to neuraminidase abolished the ability to bind the elementary bodies, whether or not polycations were present. Furthermore, at 5 degrees C but not at 37 degrees C, NeuNAc, GlcNAc and N-acetylgalactosamine inhibited chlamydial association only in the absence of the polycation DEAE-dextran. The results suggest that NeuNAc residues on the plasma membrane are the principal, but not the only, receptors for this strain of C. trachomatis.

Acetylgalactosamine↗
PubMed1972

Factors affecting hexose phosphorylation in Acetobacter xylinum.

Fructose was oxidized and converted to cellulose by cells of Acetobacter xylinum grown on fructose or succinate, but not by cells grown on glucose. In resting fructose-grown cells, glucose strongly suppressed fructose utilization. Extracts obtained from fructose- or succinate-grown cells catalyzed the adenosine triphosphate (ATP)-dependent formation of the 6-phosphate esters of glucose and fructose, whereas glucose-grown cell extracts phosphorylated glucose but not fructose. Fructokinase and glucokinase activities were separated and partially purified from cells grown on glucose, fructose, or succinate. Whereas fructokinase phosphorylated fructose only, glucokinase was active towards glucose and less active towards mannose and glucosamine. The optimal pH for the fructokinase was 7.4 and for the glucokinase was 8.5. The K(m) values for the fructokinase were: fructose, 6.2 mm; and ATP, 0.83 mm. The K(m) values for the glucokinase were: glucose, 0.22 mm; and ATP, 4.2 mm. Fructokinase was inhibited by glucose, glucosamine, mannose, and deoxyglucose in a manner competitive with respect to fructose, with K(i) values of 0.1, 0.14, 0.5, and 7.5 mm, respectively. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP) inhibited both kinases noncompetitively with respect to ATP. The K(i) values were: 1.8 mm (ADP) and 2.1 mm (AMP) for fructokinase, and 2.2 mm (ADP) and 9.6 mm (AMP) for glucokinase. Fructose metabolism in A. xylinum appears to be regulated by the synthesis and activity of fructokinase.

Adenosine Triphosphate↗
PubMed1975

Altered hexose transport and salt sensitivity in cyclic adenosine 3',5'-monophosphate-deficient Escherichia coli.

A cyclic adenosine 3',5'-monophosphate (cAMP)-deficient mutant strain of Escherichia coli K-12 was studied to determine the effect this cyclic nucleotide has on the overall growth and metabolism of this organism. Deficient cells were found to be more susceptible to growth inhibition by salts than were their cAMP-sufficient counterparts. The deficient cells transported alpha-methylglucoside by passive diffusion, whereas the parental cells or mutant cells grown in the presence of exogenous cAMP were able to take up alpha-methylglucoside by the normal active transport process. When viewed together with earlier studies conducted on cAMP-deficient cells, these findings support the view that cAMP plays a key role in regulating the construction and operation of the E. coli membrane system.

Ammonium Chloride↗