| [ Summary ] |
Calcium (Ca2+) plays important roles. Therefore, total body Ca2+ homeostasis is maintained by the coordinated regulation of intestinal absorption, renal reabsorption and bone metabolism. The apical Ca2+ entry pathway for the epithelial Ca2+ transport, which is regulated by PTH and/or 1,25-vitamin D3, is thought to be essential for this regulation. Recently, molecular candidates for these pathways have been identified. TRPV5 plays a critical role in renal final Ca2+ reabsorption. TRPV5 KO mice have been shown to exhibit impaired Ca 2+ reabsorption, compensatory Ca2+ absorption in the intestine and reduced bone thickness. On the other hand, TRPV6 has been shown to play a role in small intestinal Ca 2+ absorption. Genetic analysis has suggested that the TRPV6 gene is correlated with hypercalciuria and renal calcium stone formation caused by an increased Ca2+ absorption in the small intestine. Conversely, TRPV6 KO mice exhibited impaired intestinal Ca2+ absorption, resulting in secondary hyperparathyroidism with reduced bone mineral density. These facts suggest the critical roles of TRPV5/6 in total body Ca2+ homeostasis. |