Stimulation of TRPC5 cationic channels by low micromolar concentrations of lead ions (Pb2+)

Lead toxicity is long-recognised but continues to be a major public health problem. Its effects are wide-ranging and include induction of hyper-anxiety states. In general it is thought to act by interfering with Ca2+ signalling but specific targets are not clearly identified. Transient receptor potential canonical 5 (TRPC5) is a Ca2+-permeable ion channel that is linked positively to innate fear responses and unusual amongst ion channels in being stimulated by trivalent lanthanides, which include gadolinium. Here we show investigation of the effect of lead, which is a divalent ion (Pb2+). Intracellular Ca2+ and whole-cell patch-clamp recordings were performed on HEK 293 cells conditionally over-expressing TRPC5 or other TRP channels. Extracellular application of Pb2+ stimulated TRPC5 at concentrations greater than 1 μM. Control cells without TRPC5 showed little or no response to Pb2+ and expression of other TRP channels (TRPM2 or TRPM3) revealed partial inhibition by 10 μM Pb2+. The stimulatory effect on TRPC5 depended on an extracellular residue (E543) near the ion pore: similar to gadolinium action, E543Q TRPC5 was resistant to Pb2+ but showed normal stimulation by the receptor agonist sphingosine-1-phosphate. The study shows that Pb2+ is a relatively potent stimulator of the TRPC5 channel, generating the hypothesis that a function of the channel is to sense metal ion poisoning.