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TISSUE-SPECIFIC REGULATORY EFFECTS OF VITAMIN D AND ITS RECEPTOR ON CALBINDIN- D28K AND CALBINDIN-D9K

DR.ANIL BATTA

The balance between calcium and vitamin D is essential inmammalian development. Calbindin-D28K (CaBP-28K) andcalbindin-D9K (CaBP-9K) are cytosolic vitamin D– dependentcalcium-binding proteins that mediate the dynamic equilibriumof vitamin D and calcium, particularly in the absorptionof intestinal calcium, in urinary calcium excretion, and inbone formation. However, the precise roles of CaBP-28K andCaBP-9K are not well understood. CaBP-9K/CaBP-28K double-knockout (KO) mice have a normal phenotype under conditionsof normal dietary intake of calcium. Conversely, whengiven a calciumdeficient diet, these double-KO mice have greaterreductions in serum calcium levels and bone length thando wild-type mice. In this review, we summarize and interpretthe body of literature regarding the relationship of vitamin Dand its receptor with CaBP-28K and CaBP-9K in mammals.Calcium is vital to the human body. Calcium ion homeostasisis necessary for cell membrane integrity, excitability of themusculoskeletal system, blood coagulation, secretion of neurotransmittersand hormones, and myocardial contraction.Maintenance of the calcium balance requires the cooperationof numerous calcium transport proteins, including transientreceptor potential vanilloid type 5 (TRPV5) , transient receptorpotential vanilloid type 6 (TRPV6) , plasma membrane Ca2+ATPase (PMCA) [5], parvalbumins (PVs) . Calbindin-D9K(CaBP-9K) , calbindin-D28K (CaBP-28K), calretinin (CR)and sodium-calcium exchanger 1 (NCX1) Of these, CaBP-9Kand CaBP-28K are the 2 so-called vitamin D–dependent calcium-binding proteins In the modulation of calcium homeostasis,vitamin D, CaBP-9K, and CaBP-28K play important rolesin the absorption of intestinal calcium, in urinary calcium excretion,and in bone formation.