Toxic effects of the ionosphere A23187 on Chara

Abstract

Internodal cells of Chara coralina were treated with the weakly acidic ionosphere A23187 in order to examine the effects of high calcium influx on cytoplasmic processes. A23187 at concentrations of 24–40 mmol m −3 increased the influx of 45Ca by 10–20-fold, and caused large increases in the total cytoplasmic Ca 2+ content. The effects of the ionophore were similar at both pH 5 and at pH 8 although the various responses were considerably slower at high pH. In solutions containing Ca 2+ at a concentration of 0.5 mol m −3, increased calcium influx was correlated with reductions in the rate of protoplasmic streaming, strong acidification of the cytoplasm and a lowering of the ATP concentration. However, the effect on ATP concentration and protoplasmic streaming were greater when A23187 was applied in the absence of Ca 2+. This indicates that, at least in Chara, the physiological effect of A23187 are not due to increased influx of Ca 2+ across the plasma membrane. It was concluded that in view of the slow responses to A23187 these effects probably resulted from accumulation of the ionophore in organelle membranes resulting in the disruption of energy transduction and/or intracellular Ca 2+ homeostasis. In view of the widespread use of A23187, we feel that there are good reasons to be circumspect in the interruption of the physiological effects of this ionophore.