Calcium concentration, intracellular

As stated above, calcium is an extremely important cellular ion for several cellular functions. The concentration of calcium in human extracellular fluid is about 2.5 mM, while the intracellular concentration is only 100-200 nM depending on the cell type. Thus, there is 10 000-20 000 fold concentration difference between the cell interior and exterior that has to be maintained by cellular pumping mechanisms. This requires a large amount of energy. " ... 

As expected, ionomycin, a calcium ionophore, causes a sustained rise in the free intracellular concentration to approximately 450 nM (Figure 4). In this system, pardaxin induced an increase in intracellular [Ca ] only in the presence of extracellular Ca (Figure 4). These results indicate that pardaxin mediated a Ca influx but did not release Ca from intracellular stores. This influx is most probably mediated directly by pardaxin channels and possibly also indirectly by activation of the Ca channels of the chromaffin cells by the depolarization produced by the pardaxin channels (data not shown). These observations further substantiate our hypothesis 10) that transmembrane fluxes of Na and Ca are involved in the pathological action of pardaxin. 

All of these factors (ANS stimulation, blood-borne and locally produced substances) alter smooth muscle contractile activity by altering the intracellular concentration of calcium. An increase in cytosolic calcium leads to an increase in crossbridge cycling and therefore an increase in tension... 

This can be illustrated by known interactions between the cAMP and Ca2+ pathways. A first messenger that initially activates the cAMP pathway would be expected to exert secondary effects on the Ca2+ pathway at many levels via phosphorylation by PKA. First, Ca2+ channels and the inositol trisphosphate (IP3) receptor will be phosphorylated by PKA to modulate intracellular concentrations of Ca2+. Second, phospholipase C (PLC) is a substrate for PKA, and its phosphorylation modulates intracellular calcium concentrations, via the generation of IP3) as well as the activity of PKC, via the generation of DAG, and several types of CAMK. Similarly, the Ca2+ pathway exerts potent effects on the cAMP pathway, for example, by activating or inhibiting the various forms of adenylyl cyclase expressed in mammalian tissues (see Ch. 21). 

A high sodium intake and increased circulating natriuretic hormone inhibition of intracellular sodium transport, resulting in increased vascular reactivity and a rise in BP and / Increased intracellular concentration of calcium, leading to altered vascular smooth muscle function and increased peripheral vascular resistance. 

On the other hand, mercuric chloride decreased both spontaneous and evoked transmitter liberation at the frog neuromuscular junction [98] as well as the release of vasopressin from the pituitary gland [99] it was suggested that these effects are mediated via changes in the intracellular calcium ion concentration. 

Just as Class III agents can exhibit positive inotropy, some positive inotropic agents demonstrate Class III electrophysiologic activity. The increase in intracellular calcium-ion concentration produced by the inotropic... 

Figure 14-3. Signaling through protein kinase C (PKC). Activated phospholipase C cleaves the inositol phospholipid PIP2 to form both soluble (IP3) and membrane-associated (DAG) second messengers. DAG recruits PKC to the membrane, where binding of calcium ions to PKC fully activates it. To accomplish this, IP3 promotes a transient increase of intracellular concentration by binding to a receptor on the endoplasmic reticulum, which opens a channel allowing release of stored calcium ions. PIP2, phosphatidylinositol 4,5-bisphosphate DAG, diacylglycerol PLC, phospholipase C IP3, inositol trisphosphate.

Glende EA, Recknagel RO. 1991. An indirect method demonstrating that CCh-dependent hapatocyte injury is linked to a rise in intracellular calcium ion concentration. Res Common Chem Pathol Pharmacol 73 41-52. 

Dubovsky SL, Lee C, Christiano J, et al Elevated platelet intracellular calcium concentration in bipolar depression. Biol Psychiatry 29 441-450, 1991a Dubovsky SL, Lee C, Christiano J, et al Lithium lowers platelet intracellular ion concentration in bipolar patients. Lithium 2 167-174, 1991b Dubovsky SL, Murphy J, Thomas M, et al Abnormal intracellular calcium ion concentration in platelets and lymphocytes of bipolar patients. Am J Psychiatry 149 118-120, 1992a... 

Alpha receptors There are two major groups of alpha receptors, and a. Activation of postsynaptic receptors increases the intracellular concentration of calcium by activation of a phospholipase G in the cell membrane via G protein, receptor is responsible for inhibition of renin release from the kidney and for central a-adrenergically mediated blood pressure depression. 

It exerts its action by binding to receptor on surface of erythroid precursor cells. There is increase in intracellular concentration of calcium and arachidonate and changes in intracellular phosphorylation. It stimulates proliferation, maturation and haemoglobin formation by committed erythroid progenitors. 

In a series of studies, Dubovsky et al. ( 34) measured intracellular calcium ion concentrations in bipolar manic and depressed patients. They found decreases in mean concentrations in four bipolar, manic, and five bipolar, depressed, patients, in comparison with seven normothymic subjects without personal or first-degree relative histories of psychiatric disorders. Their findings were consistent with a diffuse abnormality in the mechanisms modulating intracellular calcium homeostasis. Further, this phenomenon s presence in both platelets and lymphocytes lends credence to a disruption in the cell membrane, the G-protein, or other mechanisms involved in the homeostasis of intracellular calcium ion concentrations. This may also support an extension of their findings from peripheral to neuronal tissue. 

Dubovsky SL, Murphy J, Thomas M, et al. Abnormal intracellular calcium ion concentration in platelets and lymphocytes of bipolar patients. Am J Psychiatry 1992 149 118-120. 

This antiporter (NCX) uses the sodium gradient to move calcium against its concentration gradient from the cytoplasm to the extracellular space. Extracellular concentrations of these ions are much less labile than intracellular concentrations under physiologic conditions. The sodium-calcium exchanger s ability to carry out this transport is thus strongly dependent on the intracellular concentrations of both ions, especially sodium. 

Konishi, M., Kurihara, S. and Sakai, T. (1985). Change in Intracellular Calcium Ion Concentration Induced by Caffeine and Rapid Cooling in Frog Skeletal Muscle Fibres. J Physiol 365 131-46. 

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