Inhibition of TRPC4/5 Channel Is Effective in Protecting against Histamine-Induced Hyperpermeability by Blocking Ca2+ Influx in Lung Microvascular Endothelial Cells

Dysfunction of lung microvascular endothelium is a major feature in the pathobiology of pulmonary edema and hypoxic respiratory failure. Histamine induces lung microvascular endothelial barrier disruption and hyperpermeability upon evoking intracellular CA²⁺ ([CA²⁺]_i) dynamics via binding to its receptors. Transient receptor potential canonical (TRPC) channels are CA²⁺-permeable channel and stimulated by the agonists of G-protein-coupled receptors (GPCR). Here, we assessed histamine induced [CA²⁺]_i increases in human lung microvascular endothelial cells (HLMVEC) by using live cell CA²⁺ imaging. We found that histamine increased [CA²⁺]_i was maintained at a static elevated level after a transient peak. The elevated CA²⁺ plateau was vanished when extracellular CA²⁺ was removed, indicating CA²⁺ influx from extracellular mediated the histamine-induced CA²⁺ plateau. TRPC4/5 channels antagonists, ML204 (10 µM) and HC070 (1 µM), significantly inhibited the CA²⁺ plateaus, which was not influenced by Pyr3 or larixyl, the antagonists of TRPC3/6. Furthermore, ML204 or HC070 effectively suppressed the permeability response to histamine in HLMVEC. Our results indicated that histamine-induced CA²⁺ influx may be mediated by TRPC4/5 channels and the antagonist of the channel significantly improved histamine-induced HLMVEC dysfunction.