PubMed · 897496
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R D Liechty. Elevated serum calcium.. https://pubmed.ncbi.nlm.nih.gov/897496/
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The relationship between depleting effects of polychlorinated biphenyls (PCBs) on the intracellular calcium store and PCBs-induced cell death in dopaminergic cells has not been fully evaluated. Here, we evaluated the effects of inhibitors of the release of ER-stored calcium on the cytotoxicities induced by 10 microg/ml of Aroclor 1254 (A1254; polychlorinated biphenyl mixture) in a catecholaminergic cell-line, CATH.a cells. Exposure to A1254 produced an elevation in free calcium ([Ca2+]i) in the presence or absence of extracellular calcium and decreased in cell viability. From our results, we deduced that the A1254-induced elevation of [Ca2+]i resulted from the depletion of ER-stored calcium. The [Ca2+)]i elevation was dramatically inhibited by an inositol 1,4,5-triphosphate receptor (IP3R) antagonist, and slightly inhibited by a ryanodine receptor (RyR) blocker. IP3R blockers conferred significant protection against A1254-induced cell death, as did RyR blockers, but calcium chelators or NMDA blockers did not. However, none of these reagents inhibited the depletion of intracellular dopamine by A1254 indicating that the mechanism of PCB-induced dopamine depletion may be independent of calcium alterations. Taken together, these data suggest that agents inhibiting the receptor-mediated depletion of stored calcium can prevent the A1254-induced cell death, but not modulate the A1254-induced intracellular dopamine depletion in CATH.a cells.
We have analyzed the mechanism of one-electron reduction of adriamycin (Adr) using recombinant full-length human neuronal nitric-oxide synthase and its flavin domains. Both enzymes catalyzed aerobic NADPH oxidation in the presence of Adr. Calcium/calmodulin (Ca(2+)/CaM) stimulated the NADPH oxidation of Adr. In the presence or absence of Ca(2+)/CaM, the flavin semiquinone radical species were major intermediates observed during the oxidation of the reduced enzyme by Adr. The FAD-NADPH binding domain did not significantly catalyze the reduction of Adr. Neither the FAD semiquinone (FADH*) nor the air-stable semiquinone (FAD-FMNH*) reacted rapidly with Adr. These data indicate that the fully reduced species of FMN (FMNH(2)) donates one electron to Adr, and that the rate of Adr reduction is stimulated by a rapid electron exchange between the two flavins in the presence of Ca(2+)/CaM. Based on these findings, we propose a role for the FAD-FMN pair in the one-electron reduction of Adr.
We report here on the stability and folding of the 91 residue alpha-helical F29W N-terminal domain of chicken skeletal muscle troponin C (TnC(1-91)F29W), the thin filament calcium-binding component. Unfolding was monitored by differential scanning calorimetry, circular dichroism, and intrinsic fluorescence spectroscopy using urea, pH, and temperature as denaturants, in the absence and in the presence of calcium. The unfolding of TnC(1-91)F29W was reversible and did not follow a two-state transition, suggesting that an intermediate may be present during this reaction. Our results support the hypothesis that intermediates are likely to occur during the folding of small proteins and domains. The physiological significance of the presence of an intermediate in the folding pathway of troponin C is discussed.