Ca²⁺-triggers massive exocytosis in Chinese hamster ovary cells

We have tracked the cell surface area of CHO cells by measuring the membrane capacitance, C(m). An increase in cytosolic [Ca²⁺], [Ca²⁺](i), increased the cell surface area by 20-30%. At micromolar [Ca²⁺](i) the increase occurred in minutes, while at 20 μM or higher [Ca²⁺](i) it occurred in seconds and was transient. GTPγS caused a 3% increase even at 0.1 μM [Ca²⁺](i). We conclude that CHO cells, previously thought capable only of constitutive exocytosis, can perform Ca²⁺-triggered exocytosis that is both massive and rapid. Ca²⁺-triggered exocytosis was also observed in 3T3 fibroblasts. Our findings add evidence to the view that Ca induces exocytosis in cells other than known secretory cells.