has been reported that thrombin causes an endothelium-dependent relaxation of arteries4'15 and produces a contraction of veins that is only partially inhibited by endothelium removal.'4 Recently, thrombin has been shown to increase the intracellular inositol 1,4,5trisphosphate (InsP3) level and free [Ca'+] ([Ca2"]i) and to produce change in pHi in cultured smooth muscle cells from rat aorta.16'17 The aim of the present study was to characterize the electrophysiological effects of thrombin on

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... cular smooth muscle cells isolated from rat portal vein and to identify the mechanisms that potentially could underlie thrombin actions. Materials and Methods Cell Preparation Wistar rats (150 g) were stunned and then killed by cervical dislocation. The portal vein was cut into several pieces, incubated for 10 minutes in low-calcium (40 ,M) physiological saline solution (PSS; composition is given below), and then incubated in low-calcium PSS containing 1.4 mg/ml collagenase, 0.5 mg/ml pronase, and 1 mg/ml bovine serum albumin at 37°C for 20 minutes. After this time, the solution was removed, and the pieces of vein were incubated again in a fresh enzyme solution at 37°C for 20 minutes. Tissues were then placed in enzyme-free solution and triturated using a by guest on