Figure 510

The calcium-ion sensing receptor (CaSR). The CaSR is a guanosine triphosphate (GTP) or G-protein-coupled polypeptide receptor. The human CaSR has approximately 1084 amino acid residues. The CaSR mediates the effects of Ca on parathyroid and renal tissues. CaSR also can be found in thyroidal C cells, brain cells, and in the gastrointestinal tract. The CaSR allows Ca to act as a first messenger on target tissues and then act by way of other second-messenger systems (eg, phospholipase enzymes and cyclic adenosine monophosphate). Within parathyroid cells, hypercalcemia increases CaSR-Ca binding, which activates the G-protein. The G-protein then activates the phospholipase C-|3-1-phosphatidylinosi-tol-4,5-biphosphate pathway to increase intracellular Ca, which then decreases translation of parathyroid hormone (PTH), decreases PTH secretion, and increases PTH degradation. The CaSR also is an integral part of Ca homeostasis within the kidney. The gene for CaSR is located on human chromosome 3q13 [3,4,7,14-16]. PKC—protein kinase C; HS—hydrophobic segment; NH2—amino terminal. (From Hebert and Brown [4]; with permission.)

0 0

Post a comment