CONTRACTION OF HUMAN HEPATIC STELLATE CELLS ACTIVATED IN CULTURE - A ROLE FOR VOLTAGE-OPERATED CALCIUM CHANNELS

Background/Aims: Voltage-operated calcium channels are essential for t he regulation of vascular tone and are potential targets for vasodilat ing agents. They regulate calcium entry and thereby cell contraction i n vascular cell types. Hepatic stellate cells in the activated phenoty pe have contractile properties and could participate in the regulation of sinusoidal blood flow Thus, this study was aimed at investigating the presence of voltage-operated calcium channels in human hepatic ste llate cells activated in culture and the effects of their stimulation on intracellular calcium concentration ([Ca2+](i)) and cell contractil ity, Methods: Binding studies using [H-3]-nitrendipine were performed to demonstrate the presence of voltage-operated calcium channels. Volt age-operated calcium channels were stimulated by causing cell membrane depolarization either by electrical field stimulation or extracellula r high potassium. [Ca2+](i) and cell contraction mere measured in indi vidual cells loaded with fura-2 using a morphometric method with an ep ifluorescence microscope coupled to a charge-coupled device-imaging sy stem. Results: Binding studies demonstrated the existence of voltage-o perated calcium channels in human activated hepatic stellate cells (7. 1+/-1.4x10(4) sites/cell with a lid of 2.1+/-0.1 nM). Both electrical field stimulation and potassium chloride-induced cell depolarization r esulted in a;marked and prolonged increase in [Ca2+](i) followed by in tense cell contraction, The degree of cell contraction correlated with the intensity of calcium peaks, Removal of extracellular calcium or p reincubation of cells with nitrendipine, a specific antagonist of volt age-operated calcium channels, completely blocked the effects on [Ca2](i) and cell contraction, whereas preincubation of cells with BayK-86 44, a specific agonist of voltage-operated calcium channels, increased calcium peaks and contraction. Conclusion: Activated human hepatic st ellate cells have a large number of voltage-operated calcium channels, the activation of which is associated with an increase in [Ca2+](i) f ollowed by marked cell contraction. Voltage-operated calcium channels probably play an important role in the regulation of activated hepatic stellate cells contractility.