Mitochondria isolated from the gill tissues of the fishSarothredon mossambica were analysed for their macromolecular content, following transfer from freshwater to media of higher salinity. The results suggest a breakdown of mitochondria during the initial phases of the stress and a regeneration during continued exposure. Also all the synthetic machineries, in general, seem to be triggered in gill tissue during continuous exposure to hyperosmotic media.

When the hearts of albino rats are subjected to pressure-induced stress through constriction of ascending aorta, changes in the mitochondrial functions are observed as early as 24 h after the imposition of the stress. These include the abolition of oxidative phosphorylation, decrease in the energy dependent [⁴⁵Ca]-uptake and decrease in the rate of energized swelling. A large influx of calcium ions and an increase in the fluidity of mitochondrial membranes also occur in this period. At later stages of hypertrophy (17, 28, 40%), these mitochondrial functions gradually return to normal levels.

Nick translation of intact rat heart nuclei has shown that the incorporation of [³H]-dATP is greater in hypertrophic heart nuclei than in normal heart nuclei suggesting that hypertrophic heart nuclei have more DNase I sensitive regions than normal heart nuclei. DNase I sensitivity analysis has shown that the rate and extent of digestion of myosin heavy chain genes are greater in hypertrophic than in normal heart nuclei. Dot blot hybridization analysis of myosin heavy chain transcripts from hypertrophic heart nuclei using myosin heavy chain cDNA as probe has shown that the sensitivity of myosin heavy chain genes to DNase I in hypertrophic heart nuclei correlates with myosin heavy chain gene activation and increased number of transcripts.

Exogenous addition of hemin to glucose-repressed cells ofSaccharomyces cerevisiae restores the level of Iso-1-cytochrome C messengers to that observed in derepressed cells.In vitro transcription in isolated nuclei has shown a 4-fold stimulation in the synthesis of Iso-1-cytochrome C messengers in repressed but hemin-treated and derepressed cells compared to the repressed cells. Studies onin vitro transport of RNA from isolated nuclei have revealed that there is a 50% drop in the transport of total RNA from nuclei isolated from repressed but hemin-treated and derepressed cells when compared with the nuclei from repressed cells. However, under these conditions, there is an enhanced transport of translatable RNA. Hybridization analysis of the transported RNA using Iso-1-cytochrome C gene-specific probe has shown that there is preferential transport of Iso-1-cytochrome C messengers in repressed but hemin treated and derepressed cells.