抄録
The concentration-sensitive Na+ channel (NaC; c:concentration) works as a Na+ sensor and it opens when [Na+]o changes. The present study was carried out to clarify the function of the NaC as one of the regulating factors in cell growth, using rat C6 glioma cells, since they have NaC in quantity. The image analysis of Na+ dynamics, using a Na+ indicator (SBFI) and ARGUS-50 (Hamamatsu Photonics), revealed an elevation of [Na+]i when [Na+]o was raised from normal (140 mM) to 190 mM. This increase was augmented when Na+ efflux was suppressed by inhibitors of the Na+ pump (ouabain) or of the Na+/K+/Cl− cotransporter (bumetanide). Osmolarity alteration was not important because addition of mannitol to the external solution did not introduce any changes in [Na+]i. The expression of immediate early gene egr-1, measured by the real-time PCR method, was reduced when [Na+]o was raised or when [Na+]i was elevated by a Na+ ionophore, monensin (Cell Biol Int 29:261-268, 2005). These procedures suppressed the rate of cell proliferation. When the expression of NaC was selectively inhibited by RNA interference (RNAi) techniques, both [Na+]i and the growth rate of C6 cells were less affected by [Na+]o changes, indicating that NaC was involved in cell growth (by controlling gene expression through introduction of Na+ into the cell). It is concluded that Na+ ions enter C6 glioma cells mainly through NaC, and Na+ ions regulate cell growth by controlling expression of proliferation-related genes. [J Physiol Sci. 2006;56 Suppl:S112]
