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Most in vitro systems employ the standard cell culture maintenance conditions of 95 % air with 5 % CO2 to balance medium pH, which translates to culture oxygen tensions of approximately 20 % - above the typical ≤ 6 % found in most tissues. The current investigation, therefore, aims to characterize the effect of maintenance and toxicant exposure with a particular focus on the α,β-unsaturated aldehyde, acrolein, in the presence of physiologically relevant oxygen tension using a differentiated H9c2 cardiomyoblast subclone. H9c2 cells were maintained separately in 20.1 and 5 % oxygen, after which cells were differentiated for five days, and then exposed to acrolein in media containing varying concentrations of tricarboxylic acid and glycolytic substrates. Cells were then assessed for viability and metabolism via the MTT conversion assay. H9c2 cells were assessed for mechanistic elucidation to characterize contributors to cellular death, including mitochondrial membrane potential (ΔΨm) reductions (JC-1), intracellular calcium influx (Fluo-4), and PARP activation. Exposure to acrolein in differing oxygen tensions revealed that standard culture cells are particularly sensitive to acrolein, but cells cultured in 5 % oxygen, depending on the medium pyruvate concentration, can be rescued significantly. Further, reductions in ΔΨm were reversed by co-exposure of 5-10 mM EGTA for both culture conditions, while intracellular calcium transients were noted only for standard cultures. The results demonstrate significant metabolic reprogramming which desensitizes differentiated H9c2 to acrolein-induced cytotoxicity. Further, PARP and extracellular calcium contribute to the fate of these cells exposed to acrolein, though clotrimazole-associated TRPM2 channels may not be significantly involved. Conclusively, significant alteration of toxicogenic response was noted in this cell line when cultured under physiologically relevant conditions, and may have a substantial impact on the reliability and predictive power and interpretive application of in vitro-based toxicity models cultured under standard culture conditions, depending on the parent tissue.

Acute and chronic morphine administration can significantly reduce ischemia- reperfusion injury of the rat heart. However, the molecular mechanisms mediating the protective effect of morphine are not yet fully elucidated. Concurrently, there is a lack of information about the effects of the long-term action of morphine on heart tissue. Therefore, in the first part of the project, we studied the effect of long-term administration of high doses of morphine (10 mg/kg/day, 10 days) on rat heart tissue. In the second part of the project, we investigated the effect of 1 mM morphine on viability and redox state of rat cardiomyoblast cell line H9c2 that was influenced by oxidative stress elicited by exposure to 300 μM tert-butyl hydroperoxide (t-BHP). Our experiments have shown that long-term morphine administration affected neither the amount nor the affinity of myocardial β-adrenergic receptors (β-AR), but almost doubled the number of the dominant isoforms of myocardial adenylyl cyclase (AC) V/VI and led to supersensitization of AC. At the same time, proteomic analyses revealed that long-term morphine administration was associated with significant changes in the left ventricular proteome. In particular, there was an increase in the expression of heat shock proteins (HSP). Increased expression of HSP27...