The subcellular distribution of peptide histidine isoleucine amide-27-like peptides in rat brain and their release from rat cerebral cortical slices in vitro.

The subcellular distribution of peptide histidine isoleucine amide (PHI)-27-like peptides (PLP) was investigated in rat cerebral cortex and whole rat brain in comparison with the distribution of vasoactive intestinal peptide (VIP). The highest content of PLP was found in the crude mitochondrial fraction (P2) and was also detected in the microsomal pellet. PLP was recovered in synaptosomes when further fractionation of P2 was performed. This distribution of PLP closely follows that of VIP and is suggestive of possible storage in vesicles at the nerve terminal. Basal release of PLP from rat cerebral cortical slices was below the detection limit of the PHI radioimmunoassay. However, depolarization by 55 mM potassium induced measurable PLP release. This release was calcium-dependent. These findings support the hypothesis that PLP could play a role in neurotransmission.