Fat-storing cells as liver-specific pericytes. Spatial dynamics of agonist-stimulated intracellular calcium transients.

Abstract

Liver perisinusoidal fat-storing cells (FSC) show morphological and ultrastructural characteristics similar to pericytes regulating local blood flow in other organs. In the present study we have analyzed whether FSC respond to local vasoconstrictors such as thrombin, angiotensin-II, and endothelin-1 with an increase in intracellular free calcium concentration (ICa2I1I) coupled with effective cell contraction. All agonists tested induced a rapid and dose-dependent increase in ICa2`i1 followed by a sustained phase lasting several minutes in confluent monolayers of Fura-2-loaded human FSC. Pharmacological studies performed using different Ca2+ channel blockers indicated that, at least for thrombin and angiotensin-II, the sustained phase is due to the opening of voltage-sensitive membrane Ca2" channels. To analyze the temporal and spatial dynamics of Ca2" release in response to these agonists, we performed experiments on individual Fura-2-loaded human FSC using a dual wavelength, ratiometric video imaging system. The rise inICa2"], was exclusively localized to the cytoplasm, particularly in the branching processes. Increases in ICa2"1, more than fourfold were associated with a simultaneous and transient reduction of cell area indicating reversible cell contraction. Our results indicate that the Ca2"-dependent contraction of human FSC in vitro may reflect a potential role in regulating sinusoidal blood flow in vivo. (J. Clin. Invest. 1992. 90:642-646.)

Effect of Tetrandrine on Experimental Hepatic Fibrosis Induced by Bile Duct Ligation and Scission in Rats

“…Recent investigation found that voltage-operated calcium channel (VOCC) plays an important role in the regulation of hepatic stellate cells contractility which is the marked phenotype of activated hepatic stellate cells (Berlin 1995;Bataller et al 1998). Moreover, activated hepatic stellate cells have receptors for a number of vasoconstrictor substances such as endotheline, angiotensin II, vasopressin, thrombin and thromboxan A2 (Pinzani et al 1992;Sakamoto et al 1993;Kawada et al 1993;Bataller et al 1997;Rockey 1997). Therefore, it is likely that the inhibitory effect of tetrandrine on hepatic stellate cells activation, at least in part, through the blocking of calcium channels.…”

Nitrovasodilators inhibit platelet-derived growth factor-induced proliferation and migration of activated human hepatic stellate cells

“…11,12 In their activated phenotype, stellate cells are characterized by remarkable proliferative, chemotactic, and contractile properties. Particularly, contraction of activated HSCs in response to different vasoconstrictors, including endothelin 1 and thrombin, 8,13,14 has been suggested to play an important role in the contraction of developing scar tissue, and, consequently, in the progression of portal hypertension. HSC contraction is counterbalanced by vasorelaxing agents such as nitric oxide (NO), 15 which has been proposed as a regulator of sinusoidal blood flow in the normal liver.…”

“…8,31 Briefly, after a combined digestion with collagenase/ pronase, HSCs were separated from other liver nonparenchymal cells by ultracentrifugation over gradients of stractan (Cellsep isotonic solution; Larex Inc., St. Paul, MN). Extensive characterization was performed as described previously.…”

“…8,34 Human HSCs were grown to subconfluence in complete culture medium on round glass cover slips (25-mm diameter, 0.2-mm thick) for 72 hours, and then incubated for 48 hours in SFIF medium. Cells were then loaded with 10 mol/L Fura-2AM and 15% Pluronic F-127 for 30 minutes at 22°C.…”

“…In experiments evaluating changes in cell area induced by thrombin, spatial calibration was performed by measuring division on a graticule under the same optical conditions as the rest of the experiments, as reported. 8 …”