TRPV Channels and Modulation by Hepatocyte Growth Factor/Scatter Factor in Human Hepatoblastoma (HepG2) Cells

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Using patch clamp and Ca2+ imaging techniques, we have studied Ca2+ entry pathways in human hepatoblastoma (HepG2) cells. These cells express the mRNA of TRPV1, TRPV2, TRPV3 and TRPV4 channels, but not those of TRPV5 and TRPV6. Functional assessment showed that capsaicin (10 μM), 4α-phorbol-12,13-didecanoate (4αPDD, 1 μM), arachidonic acid (10 μM), hypotonic stress, and heat all stimulated increases in [Ca2+]i within minutes. The increase in [Ca2+]i depended on extracellular Ca2+ and on the transmembrane potential, which indicated that both driving forces affected Ca2+ entry. Capsaicin also stimulated an increase in [Ca2+]i in nominally Ca2+-free solutions, which was compatible with the receptor functioning as a Ca2+ release channel. Hepatocyte growth factor/scatter factor (HGF/SF) modulated Ca2+ entry. Ca2+ influx was greater in HepG2 cells incubated with HGF/SF (20 ng/ml for 20 h) compared with non-stimulated cells, but this occurred only in those cells with a migrating phenotype as determined by presence of a lamellipodium and trailing footplate. The effect of capsaicin on [Ca2+]i was greater in migrating HGF/SF-treated cells, and this was inhibited by capsazepine. The difference between control and HGF/SF-treated cells was not found in Ca2+-free solutions. 4αPDD also had no greater effect on HGF/SF-treated cells. We conclude that TRPV1 and TRPV4 channels provide Ca2+ entry pathways in HepG2 cells. HGF/SF increases Ca2+ entry via TRPV1, but not via TRPV4. This rise in [Ca2+]i may constitute an early response of a signalling cascade that gives rise to cell locomotion and the migratory phenotype.