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

Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska 68198-5850 Submitted 4 February 2004 ; accepted in final form 18 March 2004 Studies were performed to identify the molecular component responsible for store-operated Ca 2+ entry in murine mesangial cells (MMC). Because the canonical transient receptor potential (TRPC) family of proteins was previously shown to comprise Ca 2+ -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 Ca 2+ (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 Ca 2+ concentration ([Ca 2+ ] i ). SOC was measured as the increase in [Ca 2+ ] i after extracellular Ca 2+ was increased from