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The transient receptor potential canonical 4 (TRPC4) channel is a Ca²⁺-permeable nonselective cation channel in mammalian cells and mediates a number of cellular functions. Many studies show that TRPC channels are activated by stimulation of Gα_q-phospholipase C (PLC)-coupled receptors. However, our previous study showed that the TRPC4 current was inhibited by co-expression of a constitutively active form of Gα_q (Gα_q ^Q209L). A shortage of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] in Gα_q ^Q209L may be responsible for reduced TRPC4 activity. Here, we tested this hypothesis by using a rapamycin-inducible system that regulates PI(4,5)P₂ acutely and specifically. Our results showed that the TRPC4β current was reduced by inducible Gα_q ^Q209L, but not by the mutants with impaired binding ability to PLCβ. Depletion of PI(4,5)P₂ by inducing the inositol …