TRPC4 and TRPC5 are two closely related members of the mammalian transient receptor potential cation channel family that have been implicated in important physiological functions, such as growth cone guidance and smooth muscle contraction. To further unravel the role of TRPC4 and TRPC5 in these processes in vivo, detailed information about the molecular composition of native channel complexes and their association with cellular signaling networks is needed. We therefore searched a human aortic cDNA library for novel TRPC4-interacting proteins using a modified yeast two-hybrid assay. This screen identified SESTD1, a previously uncharacterized protein containing a lipid-binding SEC14-like domain as well as spectrin-type cytoskeleton interaction domains. SESTD1 was found to associate with TRPC4 and TRPC5 via the channel's calmodulin-and inositol 1,4,5-trisphosphate receptor-binding domain. In functional studies, we demonstrate that SESTD1 binds several phospholipid species in vitro and is essential for efficient receptor-mediated activation of TRPC5. Notably, phospholipid binding to SESTD1 was Ca 2؉ -dependent. Because TRPC4 and -5 conduct Ca 2؉, SESTD1-channel signaling may be bidirectional and also couple TRPC activity to lipid signaling through SESTD1. The modulation of TRPC channel function by specific lipid-binding proteins, such as SESTD1, adds another facet to the complex regulation of these channels complementary to the previously described effects of direct channel-phospholipid interaction.Seven homologous channel proteins belong to the TRPC 3 family of nonselective cation channels. Within the TRPC family, TRPC4 and TRPC5 represent a structurally distinct subgroup that is characterized by its ability to form homo-and heteromultimeric channels with each other as well as with TRPC1 (1).Moreover, TRPC4 and TRPC5 are functionally set apart from other TRPCs by their unique activation mechanism that is dependent on phospholipase C activity but does not involve the phospholipid hydrolysis product diacylglycerol (2). Further signaling pathways, including Ca 2ϩ store depletion and diverse lipid-channel interactions, were also shown to control channel function (3-7). Nevertheless, the exact principles that govern TRPC4 and -5 gating have not been finally clarified and probably depend on the cellular context.Studies in knock-out mice showed that TRPC4 plays an important role in vascular physiology. TRPC4Ϫ/Ϫ mice have markedly reduced store-and receptor-induced endothelial Ca 2ϩ entry and impaired endothelium-dependent vasorelaxation (8). Moreover, TRPC4 knock-out strongly reduced acetylcholine-activated non-selective cation currents in visceral smooth muscle cells that are involved in the regulation of gastric motility (9). Similarly, functional expression of TRPC5 has been found in several vascular tissues, including human saphenous vein (10) and rabbit arteriolar smooth muscle cells (11). In addition, both TRPC4 and TRPC5 are strongly expressed in neuronal tissue and have been assigned functions in neurotransmitter...

TRPC channels are a family of nonselective cation channels that regulate ion homeostasis and intracellular Ca2+ signaling in numerous cell types. Important physiological functions such as vasoregulation, neuronal growth, and pheromone recognition have been assigned to this class of ion channels. Despite their physiological relevance, few selective pharmacological tools are available to study TRPC channel function. We, therefore, screened a selection of pharmacologically active compounds for TRPC modulating activity. We found that the synthetic gestagen norgestimate inhibited diacylglycerol-sensitive TRPC3 and TRPC6 with IC50s of 3–5 µM, while half-maximal inhibition of TRPC5 required significantly higher compound concentrations (>10 µM). Norgestimate blocked TRPC-mediated vasopressin-induced cation currents in A7r5 smooth muscle cells and caused vasorelaxation of isolated rat aorta, indicating that norgestimate could be an interesting tool for the investigation of TRP channel function in native cells and tissues. The steroid hormone progesterone, which is structurally related to norgestimate, also inhibited TRPC channel activity with IC50s ranging from 6 to 18 µM but showed little subtype selectivity. Thus, TRPC channel inhibition by high gestational levels of progesterone may contribute to the physiological decrease of uterine contractility and immunosuppression during pregnancy.