Isolation of pigmented granules involved in extra-retinal photoreception in Aplysia californica neurons.

Many neurons in the ganglia of Aplysia californica contain pigmented, membrane-bound granules (lipochondria), which are thought to mediate the light response of some of the neurons, including the giant cell of the abdominal ganglion. A method of isolating the lipochondria by centrifugation of ganglia homogenates has now been developed. Electron microscopy was used to demonstrate that most of the lipochondria remain morphologically intact. As shown by X-ray microanalysis, isolated lipochondria contain the same elements, including calcium, as do lipochondria in intact giant cells. The calcium can be released into the medium by treatment of the organelles with the Ca2+ ionophore A23187. It appears that the lipochondria of Aplysia ganglia are similar in their morphology, elemental content and susceptibility to the ionophore. Two pigments were isolated from the lipochondria, and chromatography and spectrophotometric studies indicated that they are beta-carotene and a "retinol-like" compound.