Exocytosis—one vesicle at a time

Localized Ca²⁺ spikes resulting from voltage-gated Ca²⁺ channels trigger membrane fusion of individual vesicles in chromaffin cells, according to Ute Becherer (Max-Planck Institute for Experimental Medicine, Göttingen, Germany), Martin Oheim (Ecole Supérieure de Physique et Chimie Industrielles, CNRS, Paris, France), and colleagues.

Ca²⁺ microdomains have been implicated in triggering hormone and transmitter release, but until now researchers have not been able to track individual vesicles and measure localized microdomain activity in the membrane to confirm the one-on-one dynamics. Oheim's team used dual-color evanescent field imaging with low affinity Ca²⁺ dyes to image near-membrane Ca²⁺ concentration and watch the fusion of individual fluorescently filled vesicles. The team finds that voltage-gated Ca²⁺ entry evokes spatially confined spikes of Ca²⁺ that trigger release of a vesicle's contents...