Hepatic ito cells contain calcium channels: Increases with transforming growth factor‐β 1

Ito cells (fat‐storing cells) have been implicated in mechanisms of liver fibrosis, and transforming growth factor‐β1 is a key factor that stimulates collagen production by Ito cells. Moreover, Ito cells are reported to possess contractile proteins and to contract with ligands. We recently reported the presence of L‐type voltage‐operated Ca2+ channels in Kupffer cells. In this study, we examined whether Ito cells contain Ca2+ channels and also evaluated the effect of transforming growth factor‐β1 on Ca2+ channels. Cytosolic free calcium concentration was measured in individual cultured Ito cells with the fluorescent Ca2+ indicator dye fura‐2. Partial replacement of extracellular Na+ with K+ caused an increase in cytosolic free calcium, presumably as a result of transmembrane Ca2+ influx. Basal cytosolic free calcium levels were around 40 to 50 nmol/L in both control and transforming growth factor‐β1—treated cells. In transforming growth factor‐β1—treated cells, cytosolic free calcium increased in response to K+ at values as low as 10 mmol/L, whereas untreated cells did not respond. Half‐maximal increases in cytosolic free calcium in transforming growth factor‐β1—treated cells were observed with 63 ± 6 mmol/L K+. With 100 mmol/L K+, intracellular free calcium increased around fourfold above basal values in transforming growth factor‐β1—treated cells but was only increased about twofold in untreated controls. We conclude that this increase in cytosolic free calcium occurs by way of voltage‐operated calcium channels; it did not occur in the absence of extracellular calcium and cannot be explained by Na+/Ca2+ exchange mechanisms. The influx of Ca2+ was only about one third as large on subsequent depolarizations and was not sensitive to the dihydropyridine‐type calcium channel agonist BAY K 8644. In contrast, Ca2+ influx was inhibited by the dihydropyridine‐type calcium channel blocker nitrendipine. These data indicate that Ito cells contain voltage‐operated Ca2+ channels. Furthermore, transforming growth factor‐β1 activates or up‐regulates these Ca2+ channels.(HEPATOLOGY 1994;20:1009‐1014)