Role overload

Orpen, C. (1982). Type A Personality as Moderator for the Effects of Role Conflict, Role Ambiguity and Role Overload on Individual Strain. Journal of Human Stress 8(2), 8-14. 

Bolino, M. C., Tumley, W. H. (2005). The personal costs of citizenship behavior The relationship between individual initiative and role overload, job stress, and work-family conflict. Journal of Applied Psychology, 90, 740-748. 

Recent studies by Crompton et al. have shown that oxidant stress may open a Ca-sensitive, non-selective pore in the inner mitochondrial membrane that is blocked by cyclosporin A (Crompton, 1990 Crompton and Costi, 1990). This pore opening results in massive mitochondrial swelling, dissipation of the transmembrane proton gradient and disruption of mitochondrial energy production (Crompton et al., 1992). Since mitochondria may play a role as a slow, high-capacity cytosolic calcium buffer (Isenberg et al., 1993), disruption of mitochondrial function may also contribute to calcium overload and cell injury. 

Iron overload is known to be toxic and potentially fatal. The major pathological effects of hepatic iron overload are fibrosis and cirrhosis, and hepatocellular carcinoma (Bonkovsky, 1991). The role of free radicals in the pathology of hepatic iron overload has been the subject of a detailed review recently (Bacon and Britton, 1990). 

Bacon, B.R. and Britton, R.S. (1989). Hepatic injury in chronic iron overload role of lipid peroxidation. Chem. Biol. Interact. 70, 183-226. 

Chiueh, C.C., Miyake, J., Peng, M.T. Role of dopamine autoxidation, hydroxyl radical generation, and calcium overload in underlying mechanisms involved in MPTP-induced parkinsonism. Adv. Neurol. 60 251, 1993. 

In mammals, as in yeast, several different metallothionein isoforms are known, each with a particular tissue distribution (Vasak and Hasler, 2000). Their synthesis is regulated at the level of transcription not only by copper (as well as the other divalent metal ions cadmium, mercury and zinc) but also by hormones, notably steroid hormones, that affect cellular differentiation. Intracellular copper accumulates in metallothionein in copper overload diseases, such as Wilson s disease, forming two distinct molecular forms one with 12 Cu(I) equivalents bound, in which all 20 thiolate ligands of the protein participate in metal binding the other with eight Cu(I)/ metallothionein a molecules, with between 12-14 cysteines involved in Cu(I) coordination (Pountney et ah, 1994). Although the role of specific metallothionein isoforms in zinc homeostasis and apoptosis is established, its primary function in copper metabolism remains enigmatic (Vasak and Hasler, 2000). 

Overproduction of free radicals by erythrocytes and leukocytes and iron overload result in a sharp increase in free radical damage in T1 patients. Thus, Livrea et al. [385] found a twofold increase in the levels of conjugated dienes, MDA, and protein carbonyls with respect to control in serum from 42 (3-thalassemic patients. Simultaneously, there was a decrease in the content of antioxidant vitamins C (44%) and E (42%). It was suggested that the iron-induced liver damage in thalassemia may play a major role in the depletion of antioxidant vitamins. Plasma thiobarbituric acid-reactive substances (TBARS) and conjugated dienes were elevated in (3-thalassemic children compared to controls together with compensatory increase in SOD activity [386]. The development of lipid peroxidation in thalassemic erythrocytes probably depends on a decrease in reduced glutathione level and decreased catalase activity [387]. 

Somlyo We can see that a very large fraction of the SR is continuous. I remember that the first oscillations that were reported, in muscle, were published in a paper in Nature by Professor Endo (Endo et al 1970). If we see the same mechanisms here, then the presence of the SR is at least sufficient I am not saying that it is necessary. If this is the case, then in some smooth muscles we see sufficient interconnected SR to indicate that it could play a role. In the case of skeletal muscle the overloaded SR is most likely to exhibit oscillatory phenomena. 

It was also observed in earlier studies that mitochondria not only accumulate Ca2+ as an alternative to phosphorylation of ADP (Ca2+ uptake uncouples phosphorylation from electron transport), but could also accumulate much larger amounts of Ca2+ if phosphate was also taken up, resulting in precipitation of Ca2+ within the matrix as insoluble hydroxyapatite, visible as electron-dense granules by EM. An unusual feature of these hydroxyapatite deposits is that they fail to become crystalline and remain amorphous even over protracted periods of time. Their presence in mitochondria in a number of disease conditions underlines the role for mitochondria as a sort of safety device, which can enable the cell to survive, if only for a limited period of time, situations of cytoplasmic Ca2+ overload. 

---