An essential role of PI(4,5)P^sub 2^ for maintaining the activity of the transient receptor potential canonical (TRPC)4[beta]

The transient receptor potential canonical 4 (TRPC4) channel is a Ca^sup 2+^-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 G[alpha]^sub 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 G[alpha]^sub q^ (G[alpha]^sub q^ ^sup Q209L^). A shortage of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P^sub 2^] in G[alpha]^sub q^ ^sup Q209L^ may be responsible for reduced TRPC4 activity. Here, we tested this hypothesis by using a rapamycin-inducible system that regulates PI(4,5)P^sub 2^ acutely and specifically. Our results showed that the TRPC4[beta] current was reduced by inducible G[alpha]^sub q^ ^sup Q209L^, but not by the mutants with impaired binding ability to PLC[beta]. Depletion of PI(4,5)P^sub 2^ by inducing the inositol polyphosphate 5-phosphatase to HEK293 cells that express TRPC4[beta] led to an irreversible inhibition of TRPC4[beta] currents. In contrast, inducing phosphatidylinositol 4-phosphate 5-kinase or intracellular PI(4,5)P^sub 2^ application did not activate the TRPC4[beta] current. Finally, we revealed that PI(4,5)P^sub 2^ is important in delaying the desensitization of TRPC4[beta]. Taken together, we suggest that PI(4,5)P^sub 2^ is not the activator of TRPC4[beta] activation, but it is still necessary for regulating TRPC4[beta] activation.[PUBLICATION ABSTRACT]