Calcium Hormone action

Ionized calcium is an important regulator of a variety of cellular processes, including muscle contraction, stimulus-secretion coupling, the blood clotting cascade, enzyme activity, and membrane excitability. It is also an intracellular messenger of hormone action. 

Regulatory role or role in hormone action Calcium, chromium, iodine, magnesium, manganese, sodium, potassium... 

Volume 102. Hormone Action (Part G Calmodulin and Calcium-Binding Proteins)... 

Petersen O.H., Petersen C.C., and Kasai H. 1994 Calcium and hormone action. Annu Rev Physiol 56,... 

Yamamoto K., Chadarevian A. and Pelligrini M. (1988) Juvenile hormone action mediated in male accessory glands of Drosophila by calcium and kinase C. Science 239, 916— 919. 

On the basis of results obtained from studies in adrenal glomerulosa, vascular smooth muscle and hepatic cells, it is evident that the major effects of All on cell function are mediated via an activation of the calcium messenger system. Furthermore, the data, although far from complete, provide convincing evidence that a temporal and spatial pattern of events underlies hormonal action. 

Phospholipase C A family of intracellular enzymes central to many signal transduction pathways via effects on Ca + and protein kinase C. Phospholipase C catalyzes the hydrolysis of phosphoinositol 4,5-bisphosphate to yield 1,4,5-inositol triphosphate and diacylglycerol. See Irvine, R.F., The enzymology of stimulated inositol lipid turnover. Cell Calcium 3, 295-309,1982 Farese, R.V., Phospholipids as intermediates in hormone action. Mol. Cell Endocrinol. 35,1-14,1984 Majerus, P.W., The production... 

CALCIUM The most abundant of the body s minerals an important component of bones and teeth important participant in regulation of many metabolic processes. When bound to the regulatory protein calmodulin, calcium helps modulate the activities of many enzymes. Calcium is important for blood clotting, neural and muscular activity, cell motility, hormone actions, and other activities. 

Early studies established the basic requirement of extracellular calcium ion for hormone-dependent alterations in cGMP contents (Schultz et al., 1973). Following this report, while many investigators attributed calcium participation in the hormone action through some sort of calmodulininvolving manner (Mittal and Murad, 1982), the exact mode or mechanism... 

Mittal, C. K. (1995). Oxygen-radicals/nitric oxide mediate calcium-dependent action of hormones on cyclic GMP system A novel concept in signal transduction. Mot. Cell. Biochem. in press. 

Calcium and phosphorus serve as structural components of bones and teeth and are thus required in relatively large quantities. Calcium (Ca ) plays many other roles in the body for example, it is involved in hormone action and blood clotting. Phosphorus is required for the formation of ATP and of phosphory-lated intermediates in metabolism. Magnesium activates many enzymes and also forms a complex with ATP. Iron is a particularly important mineral because it functions as a component of hemoglobin (the oxygen-carrying protein in the blood) and is part of many enzymes. Other minerals, such as zinc or molybdenum, are required in very small quantities (trace or ultra-trace amounts). 

Cyclic AMP Metabolism 530 Mode of Action of Cyclic AMP Calcium and Hormone Action 532 Conclusion 533... 

There are many examples in mammalian cells in which the effectuation of hormone action is associated with variations in calcium concentration in the different cellular compartments. Such hormonal actions include stimulation of corticosteroid secretion in the adrenal, the effect of parathyroid hormone on renal tubules, reabsorption and release of calcium from the bone, the effect of melanocyte hormone on melano-phores, the stimulation of smooth muscle contraction by acetylcholine and its retraction by epinephrine, the effect of epinephrine on heart contraction, etc. The role of calcium in the sequence of steps following the hormonal stimulus is often difficult to interpret. 

Factors controlling calcium homeostasis are calcitonin, parathyroid hormone(PTH), and a vitamin D metabolite. Calcitonin, a polypeptide of 32 amino acid residues, mol wt - SGOO, is synthesized by the thyroid gland. Release is stimulated by small increases in blood Ca " concentration. The sites of action of calcitonin are the bones and kidneys. Calcitonin increases bone calcification, thereby inhibiting resorption. In the kidney, it inhibits Ca " reabsorption and increases Ca " excretion in urine. Calcitonin operates via a cyclic adenosine monophosphate (cAMP) mechanism. 

Parathyroid hormone, a polypeptide of 83 amino acid residues, mol wt 9500, is produced by the parathyroid glands. Release of PTH is activated by a decrease of blood Ca " to below normal levels. PTH increases blood Ca " concentration by increasing resorption of bone, renal reabsorption of calcium, and absorption of calcium from the intestine. A cAMP mechanism is also involved in the action of PTH. Parathyroid hormone induces formation of 1-hydroxylase in the kidney, requited in formation of the active metabolite of vitamin D (see Vitamins, vitamin d). 

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

Angiotensin II binds to specific adrenal cortex glomerulosa cell receptors. The hormone-receptor interaction does not activate adenylyl cyclase, and cAMP does not appear to mediate the action of this hormone. The actions of angiotensin II, which are to stimulate the conversion of cholesterol to pregnenolone and of corticosterone to 18-hydroxycorticosterone and aldosterone, may involve changes in the concentration of intracellular calcium and of phospholipid metabolites by mechanisms similar to those described in Chapter 43. 

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