Differential Effects of Hypoxia on Ligand Binding Properties of Nicotinic and Muscarinic Acetylcholine Receptors on Cultured Bovine Adrenal Chromaffin Cells

Abstract: Hypoxia is known to disturb neuronal signal transmission at the synapse. Presynaptically, hypoxia is reported to suppress the release of neurotransmitters, but its postsynaptic effects, especially on the function of neurotransmitter receptors, have not yet been elucidated. To clarify the postsynaptic effects, we used cultured bovine adrenal chromaffin cells as a model of postsynaptic neurons and examined specific binding of l -[³H]nicotine (an agonist for nicotinic acetylcholine receptors: nAChRs) and ²²Na⁺ flux under control and hypoxic conditions. Experiments were performed in media preequilibrated with a gas mixture of either 21% O₂/79% N₂ (control) or 100% N₂ (hypoxia). Scatchard analysis of the specific binding to the cells revealed that the K_D under hypoxic conditions was twice as large as that under control conditions, whereas the B _max was unchanged. When the specific [³H]nicotine binding was kinetically analyzed, the association constant ( k ₁) but not the dissociation constant ( k ₋₁) was decreased to 40% of the control value by hypoxia. When the binding assay was performed using the membrane fraction, these changes were not observed. Nicotine-evoked ²²Na⁺ flux into the cells was suppressed by hypoxia. In contrast, specific [³H]quinuclidinyl benzilate binding to the intact cells was unaffected by hypoxia. These results demonstrate that hypoxia specifically suppresses the function of nAChRs (and hence, neuronal signal transmission through nAChRs), primarily by acting intracellularly.     

Correlation of the Period Length of Circadian Rhythms with the Length of Immaturity in Paramecium bursaria

The circadian photoaccumulation rhythm of thirty strains of Paramecium bursaria collected at different places in Japan and China were measured with a microcomputer assisted data collection apparatus. Although most strains showed a period of 23-26 hours in LL, we found two strains of conspicuously different periods; a short period strain (UK1, 21.8 hr) and a long period strain (T316, 28.7 hr). F1 progeny from a cross between the short and the long period strains showed an intermediate period of about 24.7 hours (range 22.5-25.8 hr). The character was not distributed in a Mendelian ratio among the F1 progeny. We isolated a mutant (E2) with short period (21.8 hr) from the stock strain Kz1 by treatment with nitrosoguanidine (MNNG). The progeny of crosses between E2 and UK1, and between E2 and T316 exhibited the short period and the normal period phenotype respectively. Moreover, the progeny from a cross between E2 and a wild type strain (Sj2w) became sexually mature about 25 fissions after conjugation. This length of immaturity is much shorter than that of the progeny from wild type strains (about 50 fissions). This early maturation character was inherited to progeny in a Mendelian ratio. Homozygotes for the early maturation allele (EM2) exhibited mating ability about 15 fissions after conjugation. These data suggest that there is a correlation between the period length of the circadian rhythm and the length of immaturity after conjugation in Paramecium bursaria.     

Gd(-) Gifu and Gd(-) Fukuoka. Two new variants of glucose-6-phosphate dehydrogenase found in Japan

Summary Two new glucose-6-phosphate dehydrogenase (G6PD) variants were discovered in Japan. The first, found in a 9-year-old male, was associated with chronic hemolysis and hemolytic crises after upper respiratory infections. The enzyme activity of the variant was 2.9% of normal. The patient's G6PD showed an increased utilization of substrate analogue, deamino-NADP, and thermal instability. The second variant occurred in a 7-year-old male with druginduced hemolysis. The main enzymatic characteristics were reduced enzyme activity, being 6.4% of normal, faster-thannormal anodal electrophoretic mobility, slightly high Michaelis constant for glucose-6-phosphate, thermal instability, and biphasic pH optima. Enzymatic properties of these variants allowed each to be distinguished from previously reported variants. The first variant was designated Gd (-) Gifu and the other, Gd (-) Fukuoka.     

A unique electrophoretic slow-moving glucose 6-phosphate dehydrogenase variant (G6PD Asahikawa) with a markedly acidic pH optimum

Summary A new glucose 6-phosphate dehydrogenase (G6PD) variant associated with chronic nonspherocytic hemolytic anemia was discovered in Japan. The patient showed hemolytic crises after upper respiratory infections. The enzyme activity was about 3.8% of the normal. The partially purified enzyme revealed slow anodal electrophoretic mobility, high Km NADP, marked thermal-instability, and increased affinity for a substrate analogue (deamino-NADP). A particular characteristic of this enzyme was a biphasic pH curve with a greatly increased activity at low pH values. From these results, this variant was clearly different from hitherto observed G6PD variants, and was designated G6PD Asahikawa.     

Formation and characterization of antibody against 2''-(5"-phosphoribosyl)-5'' AMP, the monomer form of poly(adenosine diphosphate ribose).

Specific antibody against 2'-(5"-phosphoribosyl)-5'AMP (PR-AMP), a monomer of poly(adenosine diphosphate ribose) (poly(ADP-Rib)), was produced by immunizing a rabbit with PR-AMP coupled to bovine serum albumin (BSA). Antibody against PR-AMP was purified 53-fold from serum by (NH4) 2SO4 precipitation, and BSA-Sepharose 4B, DEAE-cellulose and (PR-AMP)-BSA-Sepharose 4B column chromatographies. Inhibition experiments show that the adenine ring, 5'-phosphate residue and ribose-ribose bond of PR-AMP were essential for the antigenic determinant of PR-AMP. Anti PR-AMP antibody bound, not only with PR-AMP, but also with poly(ADP-Rib) of various chain lengths, while anti poly(ADP-Rib) antibody bound with poly(ADP-Rib) but not with PR-AMP.     

G6PD Ube, a glucose-6-phosphate dehydrogenase variant found in four unrelated Japanese families.

A total of 6,120 Japanese males were screened for glucose-6-phosphate dehydrogenase deficiency (G6PD). Five cases with the deficiency were discovered. Two of them and an additional two cases have the same variant, G6PD Ube, characterized by moderate enzyme deficiency, fast moving enzyme activity on electrophoresis, high Ki Nadph, utilization of substrate analogues, kinetics, pH optima, and stability. This variant was distinguished for G6PD A- and from other Oriental variants by biochemical parameters. Differences in the frequency and type of the variants between southern Asia and Japan, suggest that the Japanese who have been isolated on islands where malaria is not endemic, may have developed their own variant traits.     

Application of jackknife procedures to inter-experiment comparisons of parameter estimates for the Michaelis-Menten equation.

The jackknife procedure is introduced as a means of making comparisons among Michaelis-Menten parameter estimates for six different experimental conditions. In addition to providing a solution to the general inter-experimental comparison problem, the jackknife procedure will provide valid parameter estimates even when some of the assumptions usually required for statistical analysis are violated, e.g., the random errors are not normally distributed and the variances are not homogeneous. Other recent variations of the jackknife have also been introduced and briefly investigated: (i) the linear jackknife, which is more efficient computationally, and (ii) the weighted jackknife, which reduces the influence of design points (substrate concentrations) that have an excessive influence on the precision of parameter estimates.     

Natural occurence of a biopolymer, poly (adenosine diphosphate ribose).

Evidence for the natural occurrence of poly(adenosine diphosphate ribose) in vivo was obtained using a sensitive radioimmunoassay and poly(adenosine diphosphate ribose) glycohydrolase, which specifically hydrolyzes poly(adenosine diphosphate ribose). Calf thymus, liver, kidney, brain, pancreas and spleen contained poly(adenosine diphosphate ribose). Naturally occurring poly(adenosine diphosphate ribose) in calf thymus is composed of molecules of various chain lengths, like that synthesized by an in vitro system. Calf thymus was estimated to contain about 0.02 microgram/mg DNA of poly(adenosine diphosphate ribose).     

Drug residue formation from ronidazole, a 5-nitroimidazole. III. Studies on the mechanism of protein alkylation in vitro

Ronidazole (1-methyl-5-nitroimidazole-2-methanol carbamate) is reductively metabolized by liver microsomal and purified NADPH-cytochrome P-450 reductase preparations to reactive metabolites that covalently bind to tissue proteins. Kinetic experiments and studies employing immobilized cysteine or blocked cysteine thiols have shown that the principal targets of protein alkylation ara cysteine thiols. Furthermore, ronidazole specifically radiolabelled with 14C in the 4,5-ring, N-methyl or 2-methylene positions give rise to equivalent apparent covalent binding suggesting that the imidazole nucleus is retained in the bound residue. In contrast, the carbonyl-14C-labeled ronidazole gives approx. 6--15-fold less apparent covalent binding indicating that the carbamoyl group is lost during the reaction leading to the covalently bound metabolite. The conversion of ronidazole to reactive metabolite(s) is quantitative and reflects the amazing efficiency by which this compound is activated by microsomal enzymes. However, only about 5% of this metabolite can be accounted for as protein-bound products under the conditions employed in these studies. Consequently, approx. 95% of the reactive ronidazole metabolite(s) can react with other constituents in the reaction media such as other thiols or water. Based on these results, a mechanism is proposed for the metabolic activation of ronidazole.