Effects of calcium on the mechanical properties of the capsule wall of isolated nematocysts from Calliactis polypus

Abstract Effects of Ca 2+ on the mechanical properties of the capsule wall of nematocysts isolated from acontia of the sea anemone Calliactis polypus were examined. Ca 2+ affected the position but not the slope of the regression line of the relative volume on the osmotic pressure of the external solution. The Young's modulus of the capsule wall was on the order of 1 GPa. The present results suggest that Ca 2+ changes the osmotic properties of the intracapsular fluid rather than the mechanical properties of the capsule wall.