Different profiles of Ca2+ responses to endothelin-1 and PDGF in liver myofibroblasts during the process of cell differentiation.

BACKGROUND AND PURPOSE

Hepatic stellate cells play an important role in liver fibrosis but little is known about liver myofibroblasts located around the central vein and in the portal area. In this study, intracellular Ca(2+) concentration (Ca(2+)) was measured to assess the response to endothelin-1 (ET-1), platelet derived growth factor (PDGF) and ATP in rat liver myofibroblasts.

EXPERIMENTAL APPROACH

Rat liver myofibroblasts were compared in 'quiescent' (cultured on Matrigel-coated dishes) and 'activated' (cultured on non-coated plastic dishes) conditions. Ca(2+) was measured with the fluorescent dye fura-2 and mRNA for ET-1, PDGF and their receptors by RT-PCR.

KEY RESULTS

ET-1 increased Ca(2+) in quiescent cells but not in activated cells, whereas PDGF-BB increased Ca(2+) in activated cells but not in quiescent cells. However, there was no difference between responses to ATP in quiescent or activated cells. ET-1 (in quiescent cells), PDGF-BB (in activated cells) and ATP (in both cells) all induced transient increases in Ca(2+) in the absence of extracellular Ca(2+) (with EGTA), indicating the involvement of Ca(2+) release from intracellular Ca(2+) stores. The sustained increase in Ca(2+) in the presence of external Ca(2+) in activated cells (ATP and PDGF) was significantly reduced by nicardipine, a L-type Ca(2+) channel blocker, but not in quiescent cells (ATP and ET-1).

CONCLUSIONS AND IMPLICATIONS

The different pharmacological profiles of Ca(2+)-response in quiescent and activated myofibroblasts suggest that ET-1 and PDGF contribute differently to myofibroblast activation during the process of liver fibrosis.