Characterization of gastrin-releasing peptide immunoreactivity in distinct storage particles in guinea pig myenteric and Torpedo electromotor neurones.
Using high resolution centrifugal density-gradient separation of cytoplasmic extracts of guinea pig myenteric plexus and Torpedo electric tissue, we have succeeded in isolating fractions of storage particles rich in gastrin-releasing peptide (GRP). In extracts of myenteric plexus and gradients derived therefrom, the 10-amino acid GRP peptide (GRP-10) was the sole form present; this was bimodally distributed in the gradients, one peak copurifying with Golgi membranes and apparently consisting of immature storage particles, the other with other synaptophysin-rich neuropeptide-containing particles. In extracts of electric organ, a tissue rich in cholinergic electromotor nerve terminals, and gradients derived therefrom, GRP-like immunoreactivity behaved in gel permeation and reversed phase high performance liquid chromatography like the 27-amino acid peptide (GRP-27). About half of the immunoreactivity sedimented in the centrifugal gradient to a region rich in particles containing vasoactive intestinal polypeptide-like immunoreactivity; the remainder was recovered in a very dense region of the gradient containing larger membrane fragments, including synaptosomes. The electromotor nerves and cell bodies also contained GRP-27-like immunoreactivity in relatively high concentration as did the Torpedo gut. It is concluded that this GRP-like peptide is packaged in dense storage particles in the electromotor neurones.