Cardioprotective mitochondrial binding by hexokinase I is induced by a hyperoxic acute thermal insult in the rainbow trout (Oncorhynchus mykiss).

Due to the substantial photosynthetic biomass in their habitat, salmonids such as the rainbow trout (Oncorhynchus mykiss) can be subject to hyperoxia in addition to high temperatures associated with climate change. Both stressful conditions increase the incidence of damaging reactive oxygen species (ROS). The mitochondrial association of hexokinase has been shown to increase in the hearts of certain fish experiencing hypoxia in a putative cardioprotective response to oxidative stress. In this study, the mitochondrial association of hexokinase I (HKI) and markers of oxidative damage and metabolic stress were probed to elucidate the cardioprotective role of hexokinase in the rainbow trout. Results showed that the co-administration of hyperoxia and hyperthermia increased the ventricular mitochondrially-bound fraction of HKI, whereas exposure to hyperthermia in normoxia had no effect; in the combined condition there was little evidence of increased stress. A second in vitro study using ventricular strips and isolated cardiomyocytes was undertaken to reconcile the cardioprotective role of HK in the rainbow trout with findings in mammalian studies, confirming that mitochondrial association of HK maintains aerobic efficiency and inhibits apoptosis. Finally, protein sequence analysis suggested that the physiological contributions of HKI and HKII in salmonids vary from those in mammals, further explaining the dynamic nature of the traditionally-inert HKI. Together, these findings help to explain the broader functions of HKI in the salmonid heart, and illustrate the role of complex environmental conditions in defining physiological responses.

Nanoparticulate-specific effects of silver on teleost cardiac contractility.

Silver nanoparticles (nAg), due to their biocidal properties, are common in medical applications and are used in more consumer products than any other engineered nanomaterial. This growing abundance, combined with their ability to translocate across the epithelium and bioaccumulate, suggests that internalized nAg may present a risk of toxicity to many organisms in the future. However, little experimentation has been devoted to cardiac responses to acute nAg exposure, even though nAg is known to disrupt ion channels even when ionic Ag+ does not. In this study, we examined the cardiac response to nAg exposure relative to a sham and an ionic AgNO3 control across cardiomyocyte survival and homeostasis, ventricular contractility, and intrinsic pacing rates of whole hearts. Our results suggest that nAg, but not Ag+ alone, inhibits force production by the myocardium, that Ag in any form disrupts normal pacing of cardiac contractions, and that these responses are likely not due to cytotoxicity. This evidence of nanoparticle-specific effects on physiology should encourage further research into nAg cardiotoxicity and other potential sublethal effects.