Recent observations, however, don t show secretion as a passive event. It s almost explosive. Scientists report that vesicles suddenly take on large amounts of water, expanding as much as 600 fold. And rather than diffusing into the outside environment, the target substance is forcefully shot from the cell. Where the classical model falls short in explaining such findings, a gel phase-transition gives a clear perspective.
Vesicles are more than a watery soup surrounded by a membrane.
They also contain a group of polymers in which the substance to be secreted is embedded. The polymers have a high negative charge and water molecules attach in organized layers. But that matrix can be condensed by certain ions that bind the polymer strands together and force the water out. As water molecules rush to form organized layers, the cross-binding ions are shot out of the cell. Almost without exception, those cross-binding ions are the very substances to be secreted.