Low extracellular calcium (Ca²⁺) promotes release of parathyroid hormone (PTH), which acts on multiple organs to maintain overall Ca²⁺ balance. In the distal part of the nephron, PTH stimulates active Ca²⁺ reabsorption via the adenylyl cyclase–cAMP–protein kinase A (PKA) pathway, but the molecular target of this pathway is unknown. The transient receptor potential vanilloid 5 (TRPV5) channel constitutes the luminal gate for Ca²⁺ entry in the distal convoluted tubule and has several putative PKA phosphorylation sites. Here, we investigated the effect of PTH-induced cAMP signaling on TRPV5 activity. Using fluorescence resonance energy transfer, we studied cAMP and Ca²⁺ dynamics during PTH stimulation of HEK293 cells that coexpressed the PTH receptor and TRPV5. PTH increased cAMP levels, followed by a rise in TRPV5-mediated Ca²⁺ influx. PTH (1 to 31) and forskolin, which activate the cAMP pathway, mimicked the stimulation of TRPV5 activity. Remarkably, TRPV5 activation was limited to conditions of strong intracellular Ca²⁺ buffering. Cell surface biotinylation studies demonstrated that forskolin did not affect TRPV5 expression on the cell surface, suggesting that it alters the single-channel activity of a fixed number of TRPV5 channels. Application of the PKA catalytic subunit, which phosphorylated TRPV5, directly increased TRPV5 channel open probability. Alanine substitution of threonine-709 abolished both in vitro phosphorylation and PTH-mediated stimulation of TRPV5. In summary, PTH activates the cAMP-PKA signaling cascade, which rapidly phosphorylates threonine-709 of TRPV5, increasing the channel9s open probability and promoting Ca²⁺ reabsorption in the distal nephron.

We investigated which transient receptor potential (TRP) channel is responsible for the nonselective cation channel (NSCC) activated by carbachol (CCh) in murine stomach with RT-PCR and the electrophysiological method. All seven types of TRP mRNA were detected in murine stomach with RT-PCR. When each TRP channel was expressed, the current-voltage relationship of mTRP5 was most similar to that recorded in murine gastric myocytes. mTRP5 showed a conductance order of Cs⁺> K⁺> Na⁺, similar to that in the murine stomach. With 0.2 mM GTPγS in the pipette solution, the current was activated transiently in both NSCC in the murine stomach and the expressed mTRP5. Both NSCC activated by CCh in murine stomach and mTRP5 were inhibited by intracellularly applied anti-G_q/11antibody, PLC inhibitor U-73122, IICR inhibitor 2-aminoethoxydiphenylborate, and nonspecific cation channel blockers La³⁺and flufenamate. There were two other unique properties. Both the native NSCC and mTRP5 were activated by 1-oleoyl-2-acetyl-sn-glycerol. Without the activation of NSCC by CCh, the NSCC in murine stomach was constitutively active like mTRP5. From the above results, we suggest that mTRP5 might be a candidate for the NSCC activated by ACh or CCh in murine stomach.

Background & Aims Excessive Ca²⁺ influx mediates many cytotoxic processes, including those associated with autoimmune inflammatory diseases such as acute pancreatitis and Sjögren syndrome. Transient receptor potential (canonical) channel (TRPC) 3 is a major Ca²⁺ influx channel in pancreatic and salivary gland cells. We investigated whether genetic or pharmacologic inhibition of TRPC3 protects pancreas and salivary glands from Ca²⁺-dependent damage. Methods We developed a Ca²⁺-dependent model of cell damage for salivary gland acini. Acute pancreatitis was induced by injection of cerulein into wild-type and Trpc3^−/− mice. Mice were also given the Trpc3-selective inhibitor pyrazole 3 (Pyr3). Results Salivary glands and pancreas of Trpc3^−/− mice were protected from Ca²⁺-mediated cell toxicity. Analysis of Ca²⁺ signaling in wild-type and Trpc3^−/− acini showed that Pyr3 is a highly specific inhibitor of Tprc3; it protected salivary glands and pancreas cells from Ca²⁺-mediated toxicity by inhibiting the Trpc3-mediated component of Ca²⁺ influx. Conclusions TRPC3-mediated Ca²⁺ influx mediates damage to pancreas and salivary glands. Pharmacologic inhibition of TRPC3 with the highly selective TRPC3 inhibitor Pyr3 might be developed for treatment of patients with acute pancreatitis and Sjögren syndrome.

Aberrant glutathione or Ca²⁺ homeostasis due to oxidative stress is associated with the pathogenesis of neurodegenerative disorders. The Ca²⁺-permeable transient receptor potential cation (TRPC) channel is predominantly expressed in the brain, which is sensitive to oxidative stress. However, the role of the TRPC channel in neurodegeneration is not known. Here, we report a mechanism of TRPC5 activation by oxidants and the effect of glutathionylated TRPC5 on striatal neurons in Huntington’s disease. Intracellular oxidized glutathione leads to TRPC5 activation via TRPC5 S-glutathionylation at Cys176/Cys178 residues. The oxidized glutathione-activated TRPC5-like current results in a sustained increase in cytosolic Ca²⁺, activated calmodulin-dependent protein kinase and the calpain-caspase pathway, ultimately inducing striatal neuronal cell death. We observed an abnormal glutathione pool indicative of an oxidized state in the striatum of Huntington’s disease transgenic (YAC128) mice. Increased levels of endogenous TRPC5 S-glutathionylation were observed in the striatum in both transgenic mice and patients with Huntington’s disease. Both knockdown and inhibition of TRPC5 significantly attenuated oxidation-induced striatal neuronal cell death. Moreover, a TRPC5 blocker improved rearing behaviour in Huntington’s disease transgenic mice and motor behavioural symptoms in littermate control mice by increasing striatal neuron survival. Notably, low levels of TRPC1 increased the formation of TRPC5 homotetramer, a highly Ca²⁺-permeable channel, and stimulated Ca²⁺-dependent apoptosis in Huntington’s disease cells (STHdh^Q111/111). Taken together, these novel findings indicate that increased TRPC5 S-glutathionylation by oxidative stress and decreased TRPC1 expression contribute to neuronal damage in the striatum and may underlie neurodegeneration in Huntington’s disease.

Transient receptor potential canonical (TRPC) channels mediate a critical part of the receptor-evoked Ca²⁺ influx. TRPCs are gated open by the endoplasmic reticulum Ca²⁺ sensor STIM1. Here we asked which stromal interaction molecule 1 (STIM1) and TRPC domains mediate the interaction between them and how this interaction is used to open the channels. We report that the STIM1 Orai1-activating region domain of STIM1 interacts with the TRPC channel coiled coil domains (CCDs) and that this interaction is essential for opening the channels by STIM1. Thus, disruption of the N-terminal (NT) CCDs by triple mutations eliminated TRPC surface localization and reduced binding of STIM1 to TRPC1 and TRPC5 while increasing binding to TRPC3 and TRPC6. Single mutations in TRPC1 NT or C-terminal (CT) CCDs reduced interaction and activation of TRPC1 by STIM1. Remarkably, single mutations in the TRPC3 NT CCD enhanced interaction and regulation by STIM1. Disruption in the TRPC3 CT CCD eliminated regulation by STIM1 and the enhanced interaction caused by NT CCD mutations. The NT CCD mutations converted TRPC3 from a TRPC1-dependent to a TRPC1-independent, STIM1-regulated channel. TRPC1 reduced the FRET between BFP-TRPC3 and TRPC3-YFP and between CFP-TRPC3-YFP upon stimulation. Accordingly, knockdown of TRPC1 made TRPC3 STIM1-independent. STIM1 dependence of TRPC3 was reconstituted by the TRPC1 CT CCD alone. Knockout of Trpc1 and Trpc3 similarly inhibited Ca²⁺ influx, and inhibition of Trpc3 had no further effect on Ca²⁺ influx in Trpc1^−/− cells. Cell stimulation enhanced the formation of Trpc1-Stim1-Trpc3 complexes. These findings support a model in which the TRPC3 NT and CT CCDs interact to shield the CT CCD from interaction with STIM1. The TRPC1 CT CCD dissociates this interaction to allow the STIM1 Orai1-activating region within STIM1 access to the TRPC3 CT CCD and regulation of TRPC3 by STIM1. These studies provide evidence that the TRPC channel CCDs participate in channel gating.