Transient receptor potential ion

The molecules that transduce noxious heat or cold are members of the transient receptor potential (TRP) receptor family. TRP proteins (Table 57-2) form tetra-meric nonselective cation channels within the plasma membrane, allowing sodium and calcium ion influx [4]. The TRPV3 channel is activated at temperatures between 31 and39°C, TRPV1 at43°C, and TRPV2 at 52-55°C. The heat pain threshold in humans is 43°C, suggesting that... 

Clapham, D. E., Montell, C., Schultz, G. and Julius, D. International Union of Pharmacology. XLIII. Compendium of voltage-gated ion channels transient receptor potential channels. Pharmacol. Rev. 55 591-596,2003. 

Clapham DE et al Compendium of voltage-gated ion channels Transient receptor potential channels. Pharmacol Rev 2003 55 591. [PMID 14657417]... 

Sour taste detects acids, i.e., protons. Several different sour taste receptor candidates such as acid-sensing ion channels (ASICs) (57), hyperpolarization-activated cyclic nucleotide-gated channels (HCNs) (58), and two pore domain potassium channels (K2PS) (59, 60) have been described in the past. In addition, recent research identified two members of the polycystic kidney disease (PKD) family of the transient receptor potential superfamily (TRP) as strong sour taste receptor candidates or as part thereof. Immunohistochemistry and in situ hybridization revealed the presence of the polycystic-kidney-disease-like ion channel PKD2L1 in subsets of taste receptor cells of mouse fungiform, vallate, and foliate papillae. These cells differ from... 

The carboxyl-terminal 469 amino acids of NompC resemble a class of ion channel proteins called TRP (transient receptor potential) channels. This region includes six putative transmembrane helices with a porelike region between the fifth and sixth helices. The amino-terminal 1150 amino acids consist almost exclusively of 29 ankyrin repeats (Figure 32.35). Ankyrin repeats are structural motifs formed by 33 amino acids folded into a hairpin loop followed by a helix-tum-helix. Importantly, in other proteins, regions with tandem arrays of these motifs mediate protein-protein interactions, suggesting that these arrays couple the motions of other proteins to the activity of the NompC channel. 

Calcium ions are mostly present in bones or chelated to biological molecules. In blood plasma, only 1% of the calcium ions present are unbound 78% is bound to albumin, 8% to citrate, and 13% to other plasma proteins. The free calcium ions are prevented from precipitating by plasma pyrophosphate. Calcium ions are also stored in the endoplasmic reticulum (ER), mostly chelated to ER-resident proteins and phosphatidylser-ine. Free calcium ions may be released through transient receptor potential channels to the cytosol where it activates numerous physiological processes. If the free calcium ion concentration of blood plasma falls, parathyroid hormone (PTH) is secreted by the parathyroid gland cells. PTH speeds up the transport of demineralized bone products by osteoclasts. In the kidney, it increases the excretion of phosphate and decreases the excretion of calcium. PTH also acts on kidney cells to make calcitriol from vitamin D, which induces calcium transporters in the intestine and osteoclasts. PTH mediates these effects by activating G-protein-coupled receptors in the kidney and osteoclasts. 

Vitamin D-mediated transcellular calcium transport also involves entry and extmsion. Calcium influx from the intestine or bone is propelled by a steep electrochemical gradient mediated by the superfamily of Transient Receptor Potential (TRP) ion channels noted above. TRP channel ion selectivity and mode of activation are extremely variable. Some are activated or regulated by ligands such as amino acid amines or small peptides, others by physical stimuli (e.g., heat), and still others by as yet unknown mechanisms. All TRP channels are Ca2+ and Na+ selective, but the selectivity for Ca2+ versus Na+ (Ca/Na ratio) varies enormously from >100 1, to <0.05 1. This variability has contributed to a confusing TRP channel nomenclature. 

Vitamin D is a fat soluble vitamin related to cholesterol. In the skin, sunlight spontaneously oxidizes cholesterol to 7-dehydrocholesterol. 7-Dehydrocholesterol spontaneously isomerizes to cholecalciferol (vitamin D3), which is oxidized in the liver to 25-hydroxy cholecalciferol and, under the influence of PTH in the kidney, to 1,25-dihy-droxy cholecalciferol (calcitriol), the active form of vitamin D. Vitamin D induces the expression of calcium ion transport proteins (calbindins) in intestinal epithelium, osteoclasts, and osteoblasts. Calbindins and transient receptor potential channels (TRPV) are responsible for the uptake of calcium from the diet. In children, the absence of sunlight provokes a deficiency of vitamin D, causing an absence of calbindins and inadequate blood calcium levels. Osteoid tissue cannot calcify, causing skeletal deformities (rickets). In the elderly, there is a loss of intestinal TRPV receptors and decreased calbindin expression by vitamin D. In both cases, the resultant low blood calcium levels cause poor mineralization during bone remodeling (osteomalacia). Rickets is the childhood expression of osteomalacia. Osteoclast activity is normal but the bone does not properly mineralize. In osteoporosis, the bone is properly mineralized but osteoclasts are overly active. 

The carboxyl-terminal 469 amino acids of NompC resemble a class of ion channel proteins called TRP (transient receptor potential) channels. This region includes six putative transmembrane helices with a pore-like region between the fifth and sixth helices. The amino-terminal 1150 amino acids consist almost exclu-... 

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