Reduction in calcium concentration induces exocytotic secretion of catecholamines from the adrenal medulla in the absence of extracellular ions.

Cat adrenal glands were perfused with a NaCl-free medium where all NaCl had been replaced by isotonic sucrose. Exocytotic secretion of catecholamines was evoked by a simple reduction in the concentration of Ca in the medium. The response required extracellular Ca and was blocked by Ca channel blockers. The results suggest that in the absence of most ions, Ca reduction itself increases permeability of the plasma membrane to Ca, thereby evoking secretion.