Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0020438 (hypercalciuria)
 2,502 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the kidney aquaporin-2 (AQP2) provides a target for hormonal regulation of water transport by vasopressin. Short-term control of water permeability occurs via vesicular trafficking of AQP2 and long-term control through changes in the abundance of AQP2 and AQP3 water channels. Defective AQP2 trafficking causes nephrogenic diabetes insipidus, a condition characterized by the kidney inability to produce concentrated urine because of the insensitivity of the distal nephron to vasopressin. AQP2 is redistributed to the apical membrane of collecting duct cells through activation of a cAMP signaling cascade initiated by the binding of vasopressin to its V2-receptor. Protein kinase A-mediated phosphorylation of AQP2 has been proposed to be essential in regulating AQP2-containing vesicle exocytosis. Cessation of the stimulus is followed by endocytosis of the AQP2 proteins exposed on the plasma membrane and their recycling to the original stores, in which they are retained. Soluble N-ethylmaleimide sensitive fusion factor attachment protein receptors (SNARE) and actin cytoskeleton organization regulated by small GTPase of the Rho family were also proved to be essential for AQP2 trafficking. Data for functional involvement of the SNARE vesicle-associated membrane protein 2 in AQP2 targeting has recently been provided. Changes in AQP2 expression/trafficking are of particular importance in pathological conditions characterized by both dilutional and concentrating defects. One of these conditions, hypercalciuria, has shown to be associated with alteration of AQP2 urinary excretion. More precisely, recent data support the hypothesis that, in vivo external calcium, through activation of calcium-sensing receptors, modulates the expression/trafficking of AQP2. Together these findings underscore the importance of AQP2 in kidney pathophysiology.
 ...
PMID:Minireview: aquaporin 2 trafficking. 1615 Sep 1

Hereditary hypophosphatemic rickets with hypercalciuria results from mutations of the renal type IIc Na-P(i) cotransporter gene, suggesting that the type IIc transporter plays a prominent role in renal phosphate handling. The goal of the present study was to investigate the regulation of the type IIc Na-P(i) cotransporter by parathyroid hormone (PTH). Type IIc Na-P(i) cotransporter levels were markedly increased in thyroparathyroidectomized (TPTX) rats. Four hours after administration of PTH, type IIc transporter protein levels were markedly decreased in the apical membrane fraction but recovered to baseline levels at 24 h. Immunohistochemical analyses demonstrated the presence of the type IIc transporter in the apical membrane and subapical compartments in the proximal tubular cells in TPTX animals. After administration of PTH, the intensity of immunoreactive signals in apical and subapical type IIc transporter decreased in the renal proximal tubular cells in TPTX rats. Colchicine completely blocked the internalization of the type IIc transporter. In addition, leupeptin prevented the PTH-mediated degradation of the type IIa transporter in lysosomes but had no effect on PTH-mediated degradation of the lysosomal type IIc transporter. In PTH-treated TPTX rats, the internalization of the type IIc transporter occurred after administration of PTH(1-34) (PKA and PKC activator) or PTH(3-34) (PKC activator). Thus the present study demonstrated that PTH is a major hormonal regulator of the type IIc Na-P(i) cotransporter in renal proximal tubules.
 ...
PMID:Parathyroid hormone-dependent endocytosis of renal type IIc Na-Pi cotransporter. 2842 36

A multiplex family was identified with biochemical and clinical features suggestive of Bartter's syndrome (BS). The eldest sibling presented with developmental delay and rickets at 4 years of age with evidence of hypercalciuria and hypokalemia. The second sibling presented at 1 year of age with urinary tract infections, polyuria, and polydipsia. The third child was born after a premature delivery with a history of polyhydramnios and neonatal hypocalcemia. Following corrective treatment she also developed hypercalciuria and a hypokalemic metabolic alkalosis. There was evidence of secondary hyperreninemia and hyperaldosteronism in all three siblings consistent with BS. Known BS genes were screened and functional assays of ROMK (alias KCNJ1, Kir1.1) were carried out in Xenopus oocytes. We detected compound heterozygous missense changes in KCNJ1, encoding the potassium channel ROMK. The S219R/L220F mutation was segregated from father and mother, respectively. In silico modeling of the missense mutations suggested deleterious changes. Studies in Xenopus oocytes revealed that both S219R and L220F had a deleterious effect on ROMK-mediated potassium currents. Coinjection to mimic the compound heterozygosity produced a synergistic decrease in channel function and revealed a loss of PKA-dependent stabilization of PIP2 binding. In conclusion, in a multiplex family with BS, we identified compound heterozygous mutations in KCNJ1. Functional studies of ROMK confirmed the pathogenicity of these mutations and defined the mechanism of channel dysfunction.
...
PMID:Identification of compound heterozygous KCNJ1 mutations (encoding ROMK) in a kindred with Bartter's syndrome and a functional analysis of their pathogenicity. 2440 Jan 61