Endoplasmic reticulum, calcium regulation

Humez, S., Legrand, G., Vanden-Abeele, F., Monet, M., Marchetti, P., Lepage, G., Crepin, A., Dewailly, E., Wuytack, F. and Prevarskaya, N., 2004, Role of endoplasmic reticulum calcium content in prostate cancer cell growth regulation by IGF and TNFalpha. J Cell Physiol 201, 201-13. 

Burdakov D., Petersen O.H., and Verkhratsky A. 2005 Intraluminal calcium as a primary regulator of endoplasmic reticulum function. Cell Calcium 38, 303-310. 

Aluminum in micromolar concentrations was found to inhibit calcium pumping in endoplasmic reticulum. The Ca2+ ATPase activity of rat brain and cerebellum was remarkably reduced and mitochondria showed increased Ca2+ release in the presence of exactly estimated 50 pmol L-1 Al3+ [67]. Aluminum was found to be an important disrupter of intracellular calcium homeostasis, interfering also with the mitochondrial Ca2+ pump, as well as activating an Na+-K+ ATPase - the antiport mechanism of ion exchange in the plasma membrane, which regulates the Ca2+-Na+ antiporter exchange [67]. 

A typical presynaptic bouton is a specialized portion of the axon. It is characterized by an active zone, a region where the presynaptic plasma membrane comes into close contact with the postsynaptic plasma membrane and an associated cluster of vesicles (De Camilli et al., 2001). A few synaptic vesicles are adjacent to the active zone and are referred to as docked vesicles. Vesicle exocytosis occurs at the active zone subsequent endocytic retrieval of vesicular components may occur both at the active zone and in the peri-active zone area (Roos and Kelly, 1999). Vesicle maturation involves acidification of the lumen, loading with the neurotransmitter, association with peripheral membrane proteins needed for exocytosis, and recapture into a vesicle cluster. The vesicle cluster is embedded in an ac tin-rich area and is generally located next to mitochondria, which provides the energy required for the vesicle cycle and neurotransmitter dynamics and to the endoplasmic reticulum whose function includes the regulation of local cytosolic calcium. 

IP3 diffuses to specialized regions of the endoplasmic reticulum and induces it to release a small amount of stored Ca " (Golovina and Blaustein, 1997). The conse-tfuent increase in cytoplasmic levels stimulates a rtumber of events in the cytoplasm, including the further activation of protein kinase C. Calcium ions directly bind to and activate calmodulin, protein kinase C, phospholipase A2, proteins of muscle fibers (troponin, caldesmon), and proteins of the cytoskeleton (geisolin, villin). One might hesitate to cali these proteins Ca-metalloenzymes. It is more accurate to say that these enzymes are regulated by calcium. 

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