Hepatic Ito cells contain calcium channels: increases with transforming growth factor-beta 1.
Ito cells (fat-storing cells) have been implicated in mechanisms of liver fibrosis, and transforming growth factor-beta 1 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-beta 1 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-beta 1-treated cells. In transforming growth factor-beta 1-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-beta 1-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-beta 1-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.(ABSTRACT TRUNCATED AT 250 WORDS)
Oide
H
H
Department of Pharmacology, University of North Carolina at Chapel Hill 27599.
Thurman
R G
RG
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002478:Cells, Cultured; D002794:Choline / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D015854:Up-Regulation
D015220:Calcium Channels; D004095:Dihydropyridines; D016212:Transforming Growth Factor beta; D009568:Nitrendipine; D002794:Choline; D011188:Potassium; D002118:Calcium