title: [The study of the Ca2+ role in cytotoxic response of human cells in culture to the action of xenobiotics].
abstract: The role of Ca2+ in mechanisms of cell death, necrosis and apoptosis is diverse and generally recognized. The purpose of this work was to study Ca2+ participation in a cytotoxic response of human cultured cells in the presence of toxic concentrations of cationic antiseptic substance poly(hexamethylene guanidine), anionic surfactant SDS and monomeric methyl methacrylate (a component of bone cement applied in surgery). Human cell line U-937 grown in suspension was used for this study. A fluorescent probe chlortetracycline was used, as an indicator of Ca2+ transport through biologic membranes. Our results show that weakly toxic concentrations of xenobiotics under study, close to the minimum toxic doses, nearly always provoke a fair but statistically significant drop in Ca2+ binding by cells. At the same time, higher toxic doses lead to significant increase in Ca2+ influx. The latter event well compares with the majority of literary data, while the mentioned decrease in Ca2+ influx at low toxic concentrations of xenobiotics presumably correlates with the initial stage of acute cytotoxic response, accompanied by a metabolic activation and enhanced resistance of cells to injuring stimuli, demonstrated by the authors elsewhere. In parallel, a possible effect of Ca(2+)-channel antagonist nifedipine was explored under conditions of cytotoxic response of cell lines U-937, A-549 and human embryonic lung fibroblasts to poly(hexamethylene guanidine). Nifedipine (10 microM) was introduced in the incubation medium simultaneously with the toxic agent, and the cells were further maintained for 5 or 24 h in culture; their viability was monitored with the microtetrasolium test or by assessment of LDH leakage into the incubation medium. The effect of nifedipine proved to be dual, depending on the applied concentration of toxic agent: at low toxic concentrations the improvement of viability could be noticed, while at more pronounced toxic doses aggravation of viability was evident. From our point of view the explanation of this result could be the following. In weakly toxic conditions, as in intact cells, Ca2+ influx is brought about by specific mechanisms, mainly through Ca(2+)-channels, that is why nifedipine partly abolishes Ca(2+)-dependent cytotoxic response. At high concentrations, cell plasma membrane is directly damaged by toxic agent, Ca2+ enters cells mainly non-specifically, so that Ca2+ antagonist cannot protect cell injury. The reason of toxic effect aggravation by nifedipine in these conditions is still waiting for its explanation.
authors.affiliation: Institute for Influenza Research, Russian Academy of Medical Sciences, St. Petersburg. eropkin@softhome.net
authors.forename: M Iu
authors.initials: MIu
authors.lastname: Eropkin
authors.forename: T D
authors.initials: TD
authors.lastname: Smirnova
authors.forename: E M
authors.initials: EM
authors.lastname: Eropkina
authors.forename: E G
authors.initials: EG
authors.lastname: Mamaeva
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D009543:Nifedipine / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D020298:U937 Cells; D015262:Xenobiotics / Q000633:toxicity*
chemical_list: D002121:Calcium Channel Blockers; D015262:Xenobiotics; D009543:Nifedipine; D002118:Calcium