Characteristics and mechanism of enzyme secretion and increase in [Ca2+]i in Saikosaponin(I) stimulated rat pancreatic acinar cells

This investigation was to reveal the characteristics and mechanism of enzyme secretion and increase in [Ca2+]i stimulated by saikosaponin(I) (SA(I)) in rat pancreatic acini. Pancreatic acini were prepared from male Wistar rats. Isolated acinar cells were suspended in Eagle's MEM solution. After adding drugs, the incubation was performed at 37 degrees for a set period of time. Amylase of supernatant was assayed using starch-iodide reaction. Isolated acinar single cell was incubated with Fura-2/AM at 37 degrees, then cells were washed and resuspended in fresh solution and attached to the chamber. Cytoplasm [Ca2+]i of a single cell was expressed by fluorescence ratio F340/F380 recorded in a Nikon PI Ca2+ measurement system. Rate course of amylase secretion stimulated by SA(I) in rat pancreatic acini appeared in bell-like shape. The peak amplitude increased depended on SA(I) concentration. The maximum rate responded to 1 x 10(-5)mol/L SA(I) was 13.1-fold of basal and the rate decreased to basal level at 30 min. CCK-8 receptor antagonist Bt(2)-cGMP markedly inhibited amylase secretion stimulated by SA(I) and the dose-effect relationship was similar to that by CCK-8. [Ca2+]i in a single acinar cell rose to the peak at 5 min after adding 5 x 10(-6)mol/L SA(I) and was 5.1-fold of basal level. In addition, there was a secondary increase after the initial peak. GDP could inhibit both the rate of amylase secretion and rising of [Ca2+]i stimulated by SA(I) in a single pancreatic acinar cell. SA(I) is highly efficient in promoting the secretion of enzymes synthesized in rat pancreatic acini and raising intracellular [Ca2+]i. Signaling transduction pathway of SA(I) involves activating special membrane receptor and increase in cytoplasm [Ca2+]i sequentially.