Vitamin D upregulates expression of ECaC1 mRNA in semicircular canal

The low luminal Ca 2+ concentration of mammalian endolymph in the vestibular labyrinth is required for normal balance. We found transcripts in primary cultures of semicircular canal duct (SCCD) epithelial cells from neonatal rats representing a complete transport system for transepithelial absorption of Ca 2+ that is comprised of the epithelial Ca 2+ channels ECaC1 (CaT2, TRPV5) and ECaC2 (CaT1, TRPV6), calbindin (calbindin-D9k, calbindin-D28k), Na +/Ca 2+ exchanger (NCX1, NCX2, and NCX3), and plasma membrane Ca 2+-ATPase (PMCA1, PMCA3, and PMCA4) by RT-PCR. Further, vitamin D receptor was also expressed in SCCD and it was found by quantitative RT-PCR that incubation for 24 h with 1,25-dihydroxyvitamin D 3 upregulated the expression of ECaC1, calbindin-D9k, and calbindin-D28k. These observations provide evidence for the first time of an ECaC-based Ca 2+ transport system in SCCD that could maintain the low Ca 2+ concentration in vestibular endolymph.