Mitochondria during development

The appearance of rat liver mitochondria during development is very similar. As has been noted, the relative volume of the parenchymal cells increases while that of the hematopoietic cells decreases. There is an increase in cell size so that at maturity the parenchymal cells are approximately 6 times larger than during prenatal development (Greengard et al, 1972). 

Calcium levels are believed to be controlled in part at least by the uptake and release of Ca2+ from mitochondria.172"174 The capacity of mitochondria for Ca2+ seems to be more than sufficient to allow the buffering of Ca2+ at low cytosol levels. Mitochondria take up Ca2+ by an energy-dependent process either by respiration or ATP hydrolysis. It is now agreed that Ca2+ enters in response to the negative-inside membrane potential developed across the inner membrane of the mitochondrion during respiration. The uptake of Ca2+ is compensated for by extrusion of two H+ from the matrix, and is mediated by a transport protein. Previous suggestions for a Ca2+-phosphate symport are now discounted. The possible alkalization of the mitochondrial matrix is normally prevented by the influx of H+ coupled to the influx of phosphate on the H - PCV symporter (Figure 10). This explains why uptake of Ca2+ is stimulated by phosphate. Other cations can also be taken up by the same mechanism. 

ATP synthase, localized to the cytosolic face of the bacterial membrane, would then face the matrix of the evolving mitochondrion (left) or chloroplast (right). Budding of vesicles from the inner chloroplast membrane, such as occurs during development of chloroplasts in contemporary plants, would generate the thyiakoid vesicles with the Fi subunit remaining on the cytosolic face, facing the chloroplast stroma. 

Recent studies have shown that P. falciparum also possesses a single mitochondrion during its erythrocytic stages (65,66) (Fig. 13.7). This mitochondrion enlarges and becomes multilobed as development proceeds. Eventually each daughter merozoite receives a lobe of the mitochrondrion, presumably complete with its own copy of the mitochondrial genome. 

Fig. 7. Di Ferent types of mitochondria as they form during development of the rat. (A) Some mitochondria with little electron dense matrix and few cristae. Epithel cell of the epidermis (rat embryo, day 17 of gestation). 1 36,000. (B) Mitochondrion with numerous parallel cristae and a matrix of intermediate electron density. Brown fat body. Adult rat. 1 36,000. (C) Typical mitochondrion with tubuh (—>) and cristae and an electron dense matrix. Differentiated liver cell, adult rat. Close spatial relationship with the rough endoplasmic reticulum (X). 1 36,000.

During acidosis, the cells of the renal tubule can respond by inserting two proteins into the apical region of the plasma membrane. (The apical part is that region that is exposed to the developing urine.) The two proteins are H,K-ATPase and H+-ATPase. H,K-ATPase, and the enzymes that act in concert with it, is better known as a component of the parietal cell where it creates stomach acid. The other proton pump of the renal tubule, which is H" -ATPase, is closely related to FoFiH" -ATPase of the mitochondrial membrane. Hence, anyone who imderstands how protons are pumped out of the mitochondrion and how stomach acid is made will clearly understand how the renal tubule can shuttle protons to the lumen of the renal tubule and into the developing urine. 

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