Calcium Ions, Effect

Urry, W. D., Krivacia, J. R., Haider, J. Calcium ion effects of notable change in elastin conformation by interacting with neutral sites. Biochem. Biophys. Res. Commun. 43, 6 (1971)... 

Pectin Methylation Changes and Calcium Ion Effects on the Texture of Fresh, Fermented, and Acidified Cucumbers... 

C. T. Yerkes and G. T. Babcock, Surface Charge Asymmetry and a Specific Calcium Ions Effect in Chloroplast Photosystem II, Biochim. Biophys. Acta 634, 19-29 (1981). 

Verapamil (Table 1), the first slow channel calcium blocker synthesized to selectively inhibit the transmembrane influx of calcium ions into cells, lowers blood pressure in hypertensive patients having good organ perfusion particularly with increased renal blood flow. Sustained-release verapamil for once a day dosing is available for the treatment of hypertension. Constipation is a prominent side effect. Headache, dizziness, and edema are frequent and verapamil can sometimes cause AV conduction disturbances and AV block. Verapamil should not be used in combination with -adrenoceptor blockers because of the synergistic negative effects on heart rate and contractile force. 

Diltiazem inhibits calcium influx via voltage-operated channels and therefore decreases intracellular calcium ion. This decreases smooth muscle tone. Diltiazem dilates both large and small arteries and also inhibits a-adrenoceptor activated calcium influx. It differs from verapamil and nifedipine by its use dependence. In order for the blockade to occur, the channels must be in the activated state. Diltiazem has no significant affinity for calmodulin. The side effects are headache, edema, and dizziness. 

Sodium C rbon te. Sodium carbonate softens water by forming insoluble calcium carbonate with calcium ions in hard water. Carbonate can also reduce calcium levels by ion pairing, although the benefit to detergency is questionable. Buildup of calcium carbonate on machine and fabrics, which can occur with time, is undesirable. Sodium carbonate [497-19-8] does not provide any suspending action. It does, however, provide alkalinity to the wash hquor and is an effective alkah. 

Calcium ion enters the system not ordy in the form of water hardness but also in the form of calcium salts contained in the sod. Other heavy-metal ions such as aluminum and ferric iron may also be present in the sod, and must be removed by an appropriate budder to achieve good sod removal. Effective budders for cotton washing are those for which the calcium dissociation constant, expressed as or —logif -, is >4 and preferably >7 (33). 

Figure 5.1 Effect of oxygen concentration on corrosion of mild steel in slowly moving water containing 165 ppm CaCl2 48-hour test, 25°C. [Courtesy of H. H. Uhlig, D. N. Triadis, and M. Stern, Effect of Oxygen, Chlorides, and Calcium Ion on Corrosion Inhibition of Iron by Polyphosphates, J. Electrochem. Soc. 102, p. 60 (1955). Reprinted with permission by The Electrochemical Society, Inc. ]...

Temperature of the system When inhibitors are used in the 0-100°C range it is usually found that higher concentrations become necessary at the higher temperatures Other inhibitors can lose their effectiveness altogether as the temperature is raised. A prime example of this is the polyphosphate type of inhibitor. This is effective in circulating systems at temperatures below about 40°C, but at higher temperatures reversion to orthophosphate can occur and this species is ineffective at the concentrations at which it will then be present. If calcium ions are present, additional loss of inhibitor will occur due to calcium phosphate precipitation. 

FIGURE 2.19 Potentiation and modulation of response through control of cellular processes, (a) Potentiation of inotropic response to isoproterenol in guinea pig papillary muscle by the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). Ordinates percent of maximal response to isoproterenol. Abscissa percent receptor occupancy by isoproterenol (log scale). Responses shown in absence (open circles) and presence (filled circles) of IBMX. Data redrawn from [7], (b) Effect of reduction in calcium ion concentration on carbachol contraction of guinea pig ileum. Responses in the presence of 2.5 mM (filled circles) and l.5mM (open circles) calcium ion in physiological media bathing the tissue. Data redrawn from [8],... 

Another major second messenger in cells is calcium ion. Virtually any mammalian cell line can be used to measure transient calcium currents in fluorescence assays when cells are preloaded with an indicator dye that allows monitoring of changes in cytosolic calcium concentration. These responses can be observed in real time, but a characteristic of these responses is that they are transient. This may lead to problems with hemi-equilibria in antagonist studies whereby the maximal responses to agonists may be depressed in the presence of antagonists. These effects are discussed more fully in Chapter 6. 

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