Expression of Na⁺/Ca²⁺ exchangers in mouse osteoclasts and their functional role during bone resorption

Abstract

The plasma membrane Na⁺/Ca²⁺ exchangers (NCXs) are bi-directional transporter that catalyzes the exchange of Na⁺ for Ca²⁺ depending on the electrochemical gradients. Mammalian NCX forms a multigene family comprising NCX 1, NCX 2 and NCX 3. However, the expression and functional role of NCXs in mammalian osteoclasts are still unknown. The aim of present study is to clarify the expression of NCX and their functional role during bone resorption in mouse osteoclasts. We examined the expression of NCX using RT-PCR, immunocytochemical and Western blotting methods. The activation of NCX during bone resorption were assessed by measurement of intracellular Ca²⁺ concentration ([Ca²⁺]_i) using fura-2 and the effect of NCX inhibitors on pit formation assay. Mouse osteoclasts were expressed NCX 1 and 3, not NCX 2 using RT-PCR, Western blotting and immunocytochemical methods. There are some isoforms in mouse osteoclasts; NCX 1.3 and 1.4 in NCX 1 and NCX 3.5 in NCX 3. Under the measurement of [Ca²⁺]_i, low or free extracellular sodium increased [Ca²⁺]_i in osteoclasts. The [Na⁺]_o free-induced [Ca²⁺]_i i increase was inhibited by NCX inhibitors. The NCX inhibitors also decreased in pit area resorbed by osteoclasts in dose dependent manner. These results suggest that NCXs are expressed in mouse osteoclasts and act as Ca²⁺ regulation during bone resorption. [J Physiol Sci. 2006;56 Suppl:S159]