Calcium plasma membrane

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. 

These cytosolic proteins contain five EF-hand domains and are able to translocate to the plasma membrane upon calcium binding [5]. In addition to the EF-hand domains, these proteins also have a hydrophobic glycine/proline-rich domain, important for their translocation to the membrane. To date five members of this... 

In addition to intracellular heme-containing proteins, big-conductance calcium-dependent K+ (BKCa) channels and calcium-spark activated transient Kca channels in plasma membrane are also tar geted by CO [3]. As well known, nitric oxide (NO) also activates BKca channels in vascular smooth muscle cells. While both NO and CO open BKCa channels, CO mainly acts on alpha subunit of BKCa channels and NO mainly acts on beta subunit of BKca channels in vascular smooth muscle cells. Rather than a redundant machinery, CO and NO provide a coordinated regulation of BKca channel function by acting on different subunits of the same protein complex. Furthermore, pretreatment of vascular smooth muscle... 

Calcium channels in the plasma membrane activated after receptor-mediated calcium release from intracellular stores. Diese channels are present in many cellular types and play pivotal roles in a multitude of cell functions. It was recently shown that Orai proteins are the pore-forming subunit of CRAC channels. They are activated by STIM proteins that sense the Ca2+ content of the endoplasmic reticulum. 

The NHR contains also the conserved Calcineurin docking site, PxlxIT, required for the physical interaction of NEAT and Calcineurin. Dephosphorylation of at least 13 serines residues in the NHR induces a conformational change that exposes the nuclear localization sequences (NLS), allowing the nuclear translocation of NEAT. Rephosphorylation of these residues unmasks the nuclear export sequences that direct transport back to the cytoplasm. Engagement of receptors such as the antigen receptors in T and B cells is coupled to phospholipase C activation and subsequent production of inositol triphosphate. Increased levels of inositol triphosphate lead to the initial release of intracellular stores of calcium. This early increase of calcium induces opening of the plasma membrane calcium-released-activated-calcium (CRAC) channels,... 

Plasma membrane channels. The most common mechanism for the movement of into smooth muscle cells Ifom the extracellular space is the electrodiffusion of Ca " ions through highly selective channels. This movement can be significant in two quite different ways. First, Ca ions carry two positive charges and, in fact, most of the inward charge movement across the plasma membrane of smooth muscle myocytes is carried by Ca. Most smooth muscle action potentials are known to be Ca " action potentials. And second, the concentration of intracellular free calcium, the second messenger, is increased by inward calcium movement. 

Calcium channels are members of the large family of proteins, including Na and channels, which become incorporated into plasma membranes, and which form intermittent aqueous pathways through which ions can move. The channels open and close. As is the case generally for membrane spanning proteins, a Ca channel is formed by a set of helical units, in this case seven, which associate to form the channel. 

Sarcoplasmic reticulum Ca -channels. In many smooth muscle cells the rise of intracellular calcium which triggers contraction comes from the flow of calcium from the SR through Ca channels. In others, the SR contributes some unknown fraction of the triggering calcium relative to the amount which comes from the extracellular space through the plasma membrane Ca -channels. There are at least two kinds of Ca -channels in the SR. 

Because of their strategic localization, astrocytes play a crucial role in maintaining the extracellular ionic homeostasis, provide energetic metabolites to neurons and remove excess of neurotransmitter in schedule with synaptic activity. In addition, the strategic location of astrocytes allows them to carefully monitor and control the level of synaptic activity. Indeed, number of papers during the last 15 years have shown that cultured astrocytes can respond to a variety of neurotransmitters with a variety of different patterns of intracellular calcium increases (Verkhratsky et al. 1998). Later on, studies performed in intact tissue preparations (acute brain slices) further established that the plasma membrane receptors can sense external inputs (such as the spillover of neurotransmitters during intense synaptic activity) and transduce them as intracellular calcium elevations, mostly via release of calcium from internal stores (Dani et al. 1992 Murphy et al. 1993 Porter and McCarthy... 

Winship IR, Plaa N, Murphy TH (2007) Rapid astrocyte calcium signals correlate with neuronal activity and onset of the hemodynamic response in vivo. J Neurosci 27 6268-6272 Wu MM, Buchanan J, Luik RM, Lewis RS (2006) Ca store depletion causes STIMl to accumulate in ER regions closely associated with the plasma membrane. J Cell Biol 174 803-813 Wyss-Coray T (2006) Inflammation in Alzheimer disease driving force, bystander or beneficial response Nat Med 12 1005-1015... 

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