TRPC4 forms store-operated Ca2+ channels in mouse mesangial cells

Studies were performed to identify the molecular component responsible for store-operated Ca2+ entry in murine mesangial cells (MMC). Because the canonical transient receptor potential (TRPC) family of proteins was previously shown to comprise Ca2+-selective and -nonselective cation channels in a variety of cells, we screened TRPC1-TRPC7 with the use of molecular methods and the fura 2 method to determine their participation as components of the mesangial store-operated Ca2+ (SOC) channel. Using TRPC-specific primers and RT-PCR, we found that cultured MMC contained mRNA for TRPC1 and TRPC4 but not for TRPC2, TRPC3, TRPC5, TRPC6, and TRPC7. Immunocytochemical staining of MMC revealed predominantly cytoplasmic expression of TRPC1 and plasmalemmal expression of TRPC4. The role of TRPC4 in SOC was determined with TRPC4 antisense and fura 2 ratiometric measurements of intracellular Ca2+ concentration ([Ca2+]i). SOC was measured as the increase in [Ca2+]i after extracellular Ca2+ was increased from