Involvement of phosphatidylinositol 4,5-bisphosphate in the desensitization of canonical transient receptor potential 5

The classic transient receptor potential channel (TRPC) is a candidate for Ca2+-permeable cation channel in mammalian cells. TRPC5 is desensitized rapidly after activation by G protein-coupled receptor. Here we investigate the mechanisms of desensitization of TRPC5 using patch-clamp recording. TRPC5 was initially activated by muscarinic stimulation using 50 mu M carbachol (CCh) and decayed rapidly in the presence of CCh (desensitization). Intracellularly-applied phosphatidylinositol 4,5-bisphosphate (PIP2) slowed the rate of desensitization. In contrast, several other phosphoinositides, including PI(3,4)P-2, PI(3,5)P-2, PI(3,4,5)P-3 and PI(4)P, had no effect on the desensitization of the TRPC5 current. This indicates that PIP2 attenuates the desensitization of the TRPC5 current in a highly selective manner. Neither wortmannin, an inhibitor of phosphatidylinositol 4-kinase, or poly-L-lysine (PLL), a scavenger of PIP2, had any effect on desensitization of the TRPC5 current. PIP2 breakdown appears to he a required step in the desensitization of TRPC5 current, but PIP2 depletion alone was insufficient for channel desensitization. TRPC5 was inhibited by cytochalasin D treatment. In mouse ileal myocytes, the desensitization of CCh-activated inward current (I-CCh) also slowed in the presence of PIP2 in recording pipettes. These results indicate that PIP2 is involved in the desensitization of TRPC5 currents.