In vitro and in vivo activation of rat hepatic stellate cells results in de novo expression of L-type voltage-operated calcium channels

Following chronic Liver injury, hepatic stellate cells (HSCs) transdifferen tiate into myofibroblast-like cells, which develop contractile properties a nd contribute to increased resistance. to blood flow. We investigated wheth er this phenotypic activation includes changes in the expression of L-type voltage-operated Ca2+ channels (VOCC), which mediate Ca2+ influx and regula te cell contraction in vascular cell types. Rat HSCs were studied in the qu iescent phenotype and after their activation in vitro (cultured on plastic for 14 days) and in vivo (isolated from rats with CCl4-induced cirrhosis). Patch-clamp studies showed Ca2+ currents through L-type VOCC in HSCs activa ted both in vitro and in vivo, whereas no currents were detected in quiesce nt HSCs. Moreover, binding studies with H-3-isradipine, a specific L-type V OCC antagonist, showed a large number of binding sites in activated HSCs, w hile no specific binding was found in quiescent HSCs. Finally, messenger RN A (mRNA) encoding L-type VOCC was not detected in quiescent HSCs as assesse d by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis, whereas it was present in activated HSCs, Stimulation of L-t ype VOCC with KCl resulted in a marked increase in [Ca2+]i followed by cell contraction in HSCs activated both in vitro and in vivo, whereas no effect s were observed in quiescent HSCs. We conclude that the activation of HSCs is associated with up-regulation of L-type VOCC that mediate Ca2+ influx an d cell contraction. These results may be relevant to the pathogenesis of po rtal hypertension.