Model of mitosis based on antagonistic changes of intracellular concentration of free calcium and magnesium ions

The roles of magnesium in biotechnology

This review highlights the important roles played by magnesium in the growth and metabolic functions of microbial and animal cells, and therefore assigns a key role for magnesium ions in biotechnology. The fundamental biochemical and physiological actions of magnesium as a regulatory cation are outlined. Such actions are deemed to be relevant in an applied sense, because Mg2+ availability in cell culture and fermentation media can dramatically influence growth and metabolism of cells. Manipulation of extracellular and intracellular magnesium ions can thus be envisaged as a relatively simplistic, but nevertheless versatile, means of physiological cell engineering. In addition, biological antagonism between calcium and magnesium at the molecular level may have profound consequences for the optimization of biotechnological processes that exploit cells. In fermentation, for example, it is argued that the efficiency of microbial conversion of substrate to product may be improved by altering Mg:Ca concentration ratios in industrial feedstocks in a way that makes more magnesium available to the cells. With particular respect to yeast-based biotechnologies, magnesium availability is seen as being crucially important in governing central pathways of carbohydrate catabolism, especially ethanolic fermentation. It is proposed that such influences of magnesium ions are expressed at the combined levels of key enzyme activation and cell membrane stabilization. The former ensures optimum flow of substrate to ethanol and the latter acts to protect yeasts from physical and chemical stress.

Ca2+, Mg2+ and (adenosine diphosphate ribose)n in cellular response to irradiation

A model of cellular response to irradiation involving adenosine diphosphate ribosylation (ADP-ribosylation) is proposed. Its main assumptions are (a) control of accessibility of sites for ADP-ribosylation in chromatin by free Ca2+/Mg2+ ratio; and (b) regulation of the Ca2+/Mg2+ ratio by factors affecting intracellular free Ca2+ concentration; the regulation would be mediated by mitochondria. The model seeks to explain the mechanism of action of radiomodifiers such as caffeine, local anaesthetics, polyamines and 2,4-dinitrophenol.

Microtubules and microfilaments in ageing hamster embryo fibroblasts in vitro

Microtubules and microfilaments were investigated in hamster lung fibroblasts, during their in vitro life-span. These cells show a senescence process characterized by a drastic phenotypic change, resulting in two phenotypes: the type 1 cells, characteristic of young cultures and the type 2 cells appearing progressively with culture passages. Microtubules and microfilaments were observed at the TEM and also visualized by the unlabelled peroxidase-anti-peroxidase method. Moreover, the susceptibility of microtubules to nocodazole was tested in type 1 and 2 cells. We could not provide evidence for a different susceptibility to the drug. However the depolymerization wave occurred centripetally in type 1 cells whilst centrifugally in type 2 cells. These observations are discussed in relationship with the early arrest of division growth of the type 2 differentiated cells.