Activation of rat hepatic stellate cells in culture is associated with increased sensitivity to endothelin 1.
The effect of endothelin (ET) 1 on intracellular Ca2+ transients in cultured rat hepatic stellate cells (HSCs) during transformation was studied by use of single-cell fluorescence. Regardless of the duration of HSC culture, ET-1 caused a BQ-123-sensitive but IRL-1038-insensitive elevation of [Ca2+]i, indicating the involvement of ETA but not ETB receptors. HSCs in early culture ("quiescent HSCs") were mildly responsive to ET-1: the ET-1 concentration required to obtain a [Ca2+]i transient in 50% of the cells (RC50) was 7 nmol/L, and all cells responded to ET-1 concentrations above 40 nmol/L. With culture time, -smooth muscle actin (-SMA) expression increased, as did the ET-1 sensitivity of cells, resulting in a shift of the RC50 value from 7 nmol/L to 13 pmol/L within 8 days. Independent of the duration of culture, ET-1 sensitivity was higher in -SMA-expressing cells. On the other hand, sensitivity of HSCs to produce a [Ca2+]i response to extracellular uridin 5'-triphosphate (UTP) or phenylephrine did not change during the activation process. There was no difference between quiescent and activated HSCs with respect to the sharing of intracellular Ca2+ stores, which could be mobilized by ET-1, UTP, and phenylephrine, respectively. The data suggest three conclusions. (1) A marked increase in ET-1 sensitivity of HSCs during the activation process suggests a potentiation of autocrine/paracrine stimulation. (2) HSCs are susceptible to -adrenergic and purinergic stimulation, but sensitivity to phenylephrine and UTP is not affected during the transformation process. (3) The ET-1-mobilizable Ca2+ store is contained in and is smaller than the Ca2+ pool, which is mobilized by phenylephrine or UTP.
Reinehr
R M
RM
Medizinische Einrichtungen der Heinrich-Heine-Universität, Klinik f ur Gastroenterologie, Hepatologie und Infektiologie, Düsseldorf, Germany.
Kubitz
R
R
Peters-Regehr
T
T
Bode
J G
JG
Häussinger
D
D
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004351:Drug Resistance / Q000502:physiology; D019332:Endothelin-1 / Q000494:pharmacology*; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D016257:Fura-2 / Q000493:pharmacokinetics; D007425:Intracellular Membranes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution
D019332:Endothelin-1; D005456:Fluorescent Dyes; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D002118:Calcium; D016257:Fura-2