Cytosolic-free calcium

Neutrophils represent an ideal system for studying osmotic effects on exocytosis. Stimulation of cytochalasin-B-treated neutrophils with the chemotactic peptide Jlf-formylmethionyl-leucyl-phenyl-alanine (FMLP) results in a rapid compound exocytosis up to 80% of lysosomal enzymes are released within 30 s (9-14). Secretion appears to be triggered by a rise in the level of cytosolic free calcium (15-18) promoted in part by entry of extracellular calcium through receptor-gated channels and in part by release of calcium that is sequestered or bound at some intracellular site (19-21). In this presentation, we augment our previously published data (22,23), which demonstrates that lysosomal enzyme release from neutrophils is inhibited under hyperosmotic conditions and that the rise in cytosolic calcium preceding secretion is inhibited as well. 

Figure 2. Reporting of cytosolic free calcium levels by indo-1. Increases in cytosolic calcium, due either to entry of extracellular calcium via calcium channels or to release of intracellular calcium sequestered in organelles such as smooth endoplasmic reticulum, results in formation of the indo-l-calcium complex. Fluorescence intensity at 400 nm (excitation at 340 nm) is proportional to the concentration of this complex the dissociation constant for this complex is about 250 nff (24), making this probe useful for detecting calcium activities in the range of 25 to 2500 nJ. ...

Kanerud, L., Hafttrom, 1. and Ringertz, B. (1990). Effect of sulphasalazine and sulphapyridine on neutrophil superoxide production role of cytosolic free calcium. Ann. Rheum. Dis. 49, 296-300. 

ATP-dependent Ca2+ pumps and Na+,Ca2+ antiporters act in concert to maintain a low concentration of free cytosolic Ca2+. The concentration of cytosolic free calcium ion, [Ca2+] , in unstimulated cells is between 10 8 and 1 O 7 mol/1, which is more than 10,000-fold lower than extracellular free Ca2+. Most intracellular Ca2+ is stored in... 

McAinsh MR, Webb AAR, Taylor JE, Hetherington AM. Stimulus-induced oscillations in guard cell cytosolic free calcium. Plant Cell 1995 7 1207-1219. 

Read ND, Allan WTG, Knight H, Knight MR, Malho R, Russell A, Shacklock PS, Trewavas AJ. Imaging and measurement of cytosolic free calcium in plant and fungal cells. JMicrosc 1992 166 57-86. 

Kiang JG, Smallridge RC. 1994. Sodium cyanide increases cytosolic free calcium evidence for activation of the reversed mode of the Na+/Ca2+ exchanger and Ca2+ mobilization from inositol trisphosphate-insensitive pools. Toxicol Appl Pharmacol 127(2) 173-181. 

Proposed mechanism by which nitroglycerin and the organic nitrates produce relaxation in vascular smooth muscle. Nitrates induce endothelial cells to release NO or a nitrosothiol (endothelium-derived releasing factor, or EDRF). EDRF activates the enzyme guanylate cyclase, which causes the generation of cyclic guanosine monophosphate (GMP), producing a decrease in cytosolic free calcium. The end result is vascular smooth muscle relaxation. SH, sulfhydryl. 

Garg, U. C., and Hassid, A. (1991). Nitric oxide decreases cytosolic free calcium in BALB/ c 3T3 fibroblasts by a cyclic GMP-independent mechanism. ]. Biol. Chem. 266, 9-12. 

Damage to the plasma membrane allows increased influx of Ca2+. The result of this will be the same as inhibition of the efflux, a rise in cytosolic free calcium. Paracetamol and carbon tetrachloride cause this increased influx. 

Depletion of ATP will also lead to a rise in intracellular Ca2+, presumably as a result of the reduction in activity of the ATPases and a reduction in other metabolic activity. The cytosolic free calcium may also rise because of release from mitochondrial stores as caused by cadmium, MPTP, and uncouplers. It seems that the crucial event is a sustained rise in cytosolic free calcium, and there are various consequences that arise from this event ... 

Peterson, C., Ratan, R. R., Shelanski, M. L., and Goldman, J. E. (1986). Cytosolic free calcium and cell spreading decrease in fibroblasts from aged and Alzheimer donors. Proc Natl Acad Sci USA 83, 7999-8001. 

Malgaroli, A., Meldolesi, J., Zallone, A. Z. Teti, A. 1989. Control of cytosolic free calcium in rat and chicken osteoclasts. The role of extracellular calcium and calcitonin. J Biol Chem 264 14342-7. 

Zaidi M, MacIntyre I, Datta, H. 1990. Intracellular calcium in the control of osteoclast function. II. Paradoxical elevation of cytosolic free calcium by verapamil. Biochem Biophys Res Commun 167 807-12. 

Other strategies include detailed studies of the changes in brain carbohydrate metabolism in ageing and how this may differ in patients with Alzheimer s disease. Changes in the composition and biophysical properties of neuronal membranes may also be of crucial importance in regulating the cytosolic free calcium, which could affect cellular homeostasis. 

The mobilization of calcium results not only in the observed transient rise in intracellular free calcium and enhanced cellular efflux, but also in a net loss of calcium from the cell (Fig. 1). Thus, total cell calcium declines with All stimulation of adrenal and vascular smooth muscle cells [44]. Furthermore, total cell calcium remains low throughout the duration of exposure to All, suggesting that the continued formation of small amounts of 1,4,5-IP3 prevents refilling of the ER pool. Upon the removal of All and the immediate reduction in IP3 concentration, total cell calcium rapidly recovers to prestimulation levels without a detectable change in cytosolic free calcium, as measured by calcium-sensitive dyes. This observation has been taken as evidence that the IP3-releasable ER pool is in direct communication with the plasma membrane and that extracellular calcium refills the pool without entering the bulk cytosol (see Ref. 45). The location of this pool within the cell (cytosolic vs. adjacent to the plasma membrane) remains a matter of controversy (see Rasmussen arid Barrett, Chapter 4). 

The calcium binding proteins calbindin D28k, calretinin and parvalbumin are members of a family of proteins characterized by the presence of calcium binding EF-hand motifs, modulated by stimulus-induced increases in cytosolic free calcium ions (Persechini et ah,... 

Staxen, I., Pical, C., Montgomery, L.T., Gray, J.E., Hetherington, A.M., and McAinsh, M.R., 1999, Abscisic acid induces oscillations in guard-cell cytosolic free calcium that involve phosphoinositide-specific phospholipase C. Proc. Natl. Acad. Sci. U.S.A. 96 1779-1784. 

McAinsh, M.R., Clayton, H., Mansfield, T.A., and Hetherington, A.M., 1996, Changes in Stomatal Behavior and Guard Cell Cytosolic Free Calcium in Response to Oxidative Stress. Plant Physiol. Ill 1031-1042. 

Satoh, E., Ishii, T, and Nishimiwa, M. 2001. The mechanism of maitotoxin-induced elevation of the cytosolic free calcium level in rat cerebrocortical synaptosomes. JpnJPharmacol 85, 98-100. 

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