The TRPC1, TRPC4, and TRPC5 proteins form homotetrameric or heterotetrameric, calcium‐permeable cation channels that are involved in various disease states. Recent research has yielded specific and potent xanthine‐based TRPC1/4/5 inhibitors. Here, we investigated the possibility of xanthine‐based activators of these channels.
An analogue of the TRPC1/4/5 inhibitor Pico145, AM237, was synthesized and its activity was investigated using HEK cells overexpressing TRPC4, TRPC5, TRPC4–C1, TRPC5–C1, TRPC1:C4 or TRPC1:C5 channels, and in A498 cells expressing native TRPC1:C4 channels. TRPC1/4/5 channel activities were assayed by measuring intracellular concentration of Ca 2+ ([Ca 2+] i) and by patch‐clamp electrophysiology. Selectivity of AM237 was tested against TRPC3, TRPC6, TRPV4, or TRPM2 channels.
AM237 potently activated TRPC5:C5 channels (EC 50 15–20 nM in [Ca 2+] i assay) and potentiated their activation by sphingosine‐1‐phosphate but suppressed activation evoked by (−)‐englerin A (EA). In patch‐clamp studies, AM237 activated TRPC5:C5 channels, with greater effect at positive voltages, but with lower efficacy than EA. Pico145 competitively inhibited AM237‐induced TRPC5:C5 activation. AM237 did not activate TRPC4:C4, TRPC4–C1, TRPC5–C1, TRPC1:C5, and TRPC1:C4 channels, or native TRPC1:C4 channels in A498 cells, but potently inhibited EA‐dependent activation of these channels with IC 50 values ranging from 0.9 to 7 nM. AM237 (300 nM) did not activate or inhibit TRPC3, TRPC6, TRPV4, or TRPM2 channels.