Ultrastructural changes associated with K+-evoked peptide secretion from a neurohemal organ of the crab, Cardisoma carnifex.

Electron-microscopic comparison of K+-stimulated and unstimulated crab sinus glands reveals significant differences in neurosecretory terminal morphology. Sinus glands exposed to elevated K+ saline for increasing periods of time show increasing numbers of exocytotic release profiles, vacuoles, and multilamellate bodies, and a decrease in the number of microvesicles within 10 micron of release sites. These morphological changes are well correlated with secretion of red-pigment-concentrating hormone, as determined by bioassay of perfusate from the individual preparations.