Ce4+-stimulated ion fluxes are responsible for apoptosis and taxol biosynthesis in suspension cultures of Taxus cells

Abstract

Ion fluxes across the plasma membrane activated by 1 mM Ce4+, cell apoptosis and taxol biosynthesis in suspension cultures ofTaxus cuspidata were studied. The extracellular pH sharply decreased upon the addition of 1 mM Ce4+, then increased gradually and exceeded the initial pH value over a time period of 12 h. The extracellular Ca2+ concentration decreased within the first 3 h after the addition of Ce4+, then gradually decreased to one third of initial value in control at about 72 h and remained unchanged afterwards. Experiments with an ion channel blocker and a Ca2+-channel blocker indicated that the dynamic changes in extracellular pH and the Ca2+ concentration resulted from the Ce4+-induced activation of H+ uptake and Ca2+ influx across the plasma membranevia ion channels. A pretreatment of the ion channel blocker initiated Ce4+-treated cells to undergo necrosis, and the prior addition of the Ca2+-channel blocker inhibited Ce4+-induced taxol biosynthesis and apoptosis. It is thus inferred that H+ uptake is necessary for cells to survive a Ce4+-caused acidic environment and is one of the mechanisms of Ce4-induced apoptosis. Furthermore, the Ca2+ influx across the plasma membrane mediated both the Ce4+-induced apoptosis and taxol biosynthesis.