Stimulation-dependent uptake of an extracellular marker to subcellular fractions of isolated neurohypophysial tissue.

Slices of ox neurohypophyses and groups of isolated rat neurointermediate lobes were incubated in a medium containing horseradish peroxidase (HRP) and stimulated by high K+ concentrations in the medium. After washing, the tissue was homogenized and subjected to subcellular fractionation in a Percoll/sucrose gradient. HRP was exclusively taken up by particles banding at a low density of the gradient. The HRP containing particles located to this region included vacuoles of a size comparable to secretory vesicles.