Figure 6.

STIM1 regulates TRPC5 but it is not obligatory for channel function. (a) STIM1 interacts with TRPC5. HEK cells were transfected with GFP–TRPC5 alone (C5); C5+ Flag–TRPC3 (C5+C3) and C5+ Flag–TRPC6 (C5+C6) and the extracts were used to immunoprecipitate native STIM1 and probe for coimmunoprecipitation of TRPC5. Note that STIM1 interacts with TRPC5 and the interaction is not affected by TRPC3 or TRPC6. (b) High levels of TRPC5 (four times more cDNA) were transfected in HEK cells treated with scrambled siRNA or with STIM1 siRNA. The current was measured in response to stimulation with carbachol, and then in response to activation of TRPC5 by La³⁺ in the same cells. Representative I/V curves are shown. (c) Histogram indicating the mean ± s.e.m. of the current density recorded in five experiments of cells expressing low or high levels of TRPC5 and treated with scrambled (control) or STIM1 siRNA. The cells were stimulated with carbachol and then activated with La³⁺. Note that knockdown of STIM1 inhibits receptor-mediated activation of TRPC5 irrespective of expression levels and that knockdown of STIM1 has no effect on activation of TRPC5 by La³⁺ in the same cells.