A self‐limiting regulation of vasoconstrictor‐activated TRPC3/C6/C7 channels coupled to PI(4,5)P2‐diacylglycerol signalling

Key points  •  From brain to digestive tract, electro-chemical signals are broadly utilized to control the activity of the organs; however, the formation of such signals is very varied in each cell and still unknown in many cells. •  In this study, we found a novel mechanism for forming an electrical signal, produced by channels of the transient receptor potential canonical (TRPC) family of channels, which allow the permeation of ions such as sodium and calcium and are opened by the actions of hormones such as adrenaline and noradrenaline. •  Such hormones can activate an enzyme (phospholipase C) by which PI(4,5)P2, a member of the membrane lipid ‘phosphoinositide’, is degraded: the degradation of PI(4,5)P2 to produce an agonist (diacylglycerol) involved in the opening of TRPC channels, while the degradation itself is surprisingly critical to the closing of these channels. •  As a result of such a self-limiting effect via membrane lipid degradation, TRPC channels can produce a unique electro-chemical signal which is tightly bound to the arrangement of membrane lipid and hormones. •  Differential sensitivity for PIP2 of TRPC Abstract  Activation of transient receptor potential (TRP) canonical TRPC3/C6/C7 channels by diacylglycerol (DAG) upon stimulation of phospholipase C (PLC)-coupled receptors results in the breakdown of phosphoinositides (PIPs). The critical importance of PIPs to various ion-transporting molecules is well documented, but their function in relation to TRPC3/C6/C7 channels remains controversial. By using an ectopic voltage-sensing PIP phosphatase (DrVSP), we found that dephosphorylation of PIPs robustly inhibits currents induced by carbachol (CCh), 1-oleolyl-2-acetyl-sn-glycerol (OAG) or RHC80267 in TRPC3, TRPC6 and TRPC7 channels, though the strength of the DrVSP-mediated inhibition (VMI) varied among the channels with a rank order of C7 > C6 > C3. Pharmacological and molecular interventions suggest that depletion of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is most likely the critical event for VMI in all three channels. When the PLC catalytic signal was vigorously activated through overexpression of the muscarinic type-I receptor (M1R), the inactivation of macroscopic TRPC currents was greatly accelerated in the same rank order as the VMI, and VMI of these currents was attenuated or lost. VMI was also rarely detected in vasopressin-induced TRPC6-like currents in A7r5 vascular smooth muscle cells, indicating that the inactivation by PI(4,5)P2 depletion underlies the physiological condition. Simultaneous fluorescence resonance energy transfer (FRET)-based measurement of PI(4,5)P2 levels and TRPC6 currents confirmed that VMI magnitude reflects the degree of PI(4,5)P2 depletion. These results demonstrate that TRPC3/C6/C7 channels are differentially regulated by depletion of PI(4,5)P2, and that the bimodal signal produced by PLC activation controls these channels in a self-limiting manner.