Involvement of Phosphatidylinositol 4,5-Bisphosphate in the Desensitization of Canonical Transient Receptor Potential 5

Abstract

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 μM 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)P₂, PI(3,5)P₂, PI(3,4,5)P₃ 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 be 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.