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 Ca2+ concentration ([Ca2+](i)) 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. [Ca2+] i 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 [Ca2+] (i) in quiescent cells but not in activated cells, whereas PDGF-BB increased [Ca2+] i 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 [Ca2+](i) in the absence of extracellular Ca2+ (with EGTA), indicating the involvement of Ca2+ release from intracellular Ca2+ stores. The sustained increase in [Ca2+](i) in the presence of external Ca2+ in activated cells (ATP and PDGF) was significantly reduced by nicardipine, a L-type Ca2+ channel blocker, but not in quiescent cells (ATP and ET-1). Conclusions and implications: The different pharmacological profiles of [Ca2+](i)-response in quiescent and activated myofibroblasts suggest that ET-1 and PDGF contribute differently to myofibroblast activation during the process of liver fibrosis.