Stimulation of histamine H₂ receptors activates TRPC3 channels through both phospholipase C and phospholipase D

Histamine plays an important role in many physiological functions; and a change in cytosolic Ca²⁺ ([Ca²⁺]_i) may be an early signal in these processes. In the present study, we investigated the activation mechanism of TRPC3, the Canonical Transient Receptors Potential 3 Channels, by histamine via a non-capacitative Ca²⁺ entry pathway. TRPC3 was transfected into HEK293 cells and the cells were treated with thapsigargin to deplete the intracellular Ca²⁺ stores; re-addition of Ca²⁺ initiated a capacitative Ca²⁺ entry (CCE). A subsequent application of histamine evoked another Ca²⁺ influx on top of the CCE signal only in the TRPC3-transfected HEK293 cells, indicating that histamine can activate TRPC3 via a non-capacitative Ca²⁺ entry pathway (non-CCE). This histamine-induced non-CCE was abolished by cimitidine, a histamine H₂ receptors antagonist, but not by histamine H₁ receptor antagonists pyrilamine and diphenhydramine. KT5720, a protein kinase A (PKA) inhibitor, had no effect on the histamine-induced non-CCE. This histamine-induced non-CCE was partially reduced by U73122, a phospholipase C (PLC) inhibitor, and by butan-1-ol, a phospholipase D (PLD) inhibitor. When both PLC and PLD inhibitors were simultaneously applied, the non-CCE signal was completely abolished. Taken together, our results showed, for the first time, that histamine could activate TRPC3 via histamine H₂ receptors, and both PLC and PLD participated in this process.