The contraction of hepatic stellate (Ito) cells stimulated with vasoactive substances

Abstract

We have studied the contractility of liver sinusoidal stellate (Ito) cells stimulated with endothelin 1, nitric-oxide donors and eicosanoids. Contraction and relaxation of stellate cells were detected by the use of a silicone-rubber method that revealed the traction forces exerted by these cells. Endothelin 1 was a strong elicitor for stellate-cell contraction. 78, 55, 59 and 56% of stellate cells were contracted 2.5, 5, 10 and 20 min, respectively, after exposure to 10 nM endothelin 1. The effect of endothelin 1 was dose dependent and still detectable at an endothelin 1 concentration of 100 pM. Concomitantly, an endothelin-dependent formation of inositol phosphates was apparent; values of Insp, InsP₂, and InsP₃ were 881±99%, 1965±368%, and 791±120% of control, respectively, 20 min after addition of 10 nM endothelin 1. In addition, endothelin 1 caused a transient increase of [Ca²⁺]_i in stellate cells from a basal value of 121±9 nM to maximal 1015±86nM. These endothelin-1 effects were much stronger than those of the thromboxane-A₂ analogue U46619 and of prostaglandin F_2a. In contrast, IIoprost, prostaglandin E₂, and sodium nitroprusside promoted stellate-cell relaxation; for example, 82, 83 and 71% of stellate cells relaxed 5, 10, and 20 min, respectively, after addition of 500μM sodium nitroprusside to contracted cells. Prostaglandin E₂ and Iloprost led to elevation of cAMP levels in stellate cells from a basal value of 9.2±0.8 pmol/well to 55.1±8.0 and 122.2±12.2 pmol/well 10 min after addition of prostaglandin E₂ (5μM), and Iloprost (5μM), respectively, in the presence of 3-isobutyl-1-methylxanthine (0.5 mM). However, sodium nitroprusside was a trigger for cGMP accumulation. Intracellular cGMP increased from a basal value of 0.9±0.007 pmol/well 13.4±6.7 pmol/well 10min after addition of 500 μM sodium nitroprusside into the medium. It is interesting that Iloprost and sodium nitroprusside also induced the disappearance of actin stress fibers in contracted cells; F-actin stress fibers became less numerous and de-aggregated; more than 90% of stellate cells were void of stress fibers after 10 μM Iloprost treatment for 30 min. Thus, endothelin 1, eicosanoids and sodium nitroprusside are able to modulate the contractility of stellate cells. The effect of endothelin 1 and prostaglandin F_2a seems to be mediated by inositol-phosphate formation and increase of the intracellular Ca²⁺ level, that of Iloprost and prostaglandin E₂ by cAMP. cGMP may be a second messenger for the action of sodium nitroprusside.