Cardiac regulation by endogenous small cardioactive peptides and FMRFamide-related peptides in the snail Helix aspersa.

The putative hepatopeptide pQDPFLRIamide, previously known only from its appearance in a cDNA clone from Helix aspersa, was isolated from circumoesophageal ganglia extracts and sequenced. Extracts of several tissues were fractionated by high performance liquid chromatography and the fractions analysed by radioimmunoassay (RIA). The results indicate that ten cardioactive peptides, FMRFamide, FLRFamide, six FMRFamide-related heptapeptides and two nonapeptide analogues of the small cardioactive peptides (SCPs), are present in the circumoesophageal ganglia (brain), the visceral nerve trunk (from which the cardiac nerve branches) and the aorta. The heart contains the two tetrapeptides, FMRFamide and FLRFamide, and the SCPs, but the heptapeptides were completely undetectable in this organ. The levels of tetrapeptide were high enough to allow their calcium-dependent release from the heart to be demonstrated. Immunohistochemistry revealed a diffuse SCP and FMRFamidergic innervation distributed throughout the heart. These data support the idea that, although the ten peptides are probably acting as neurotransmitters throughout most of the cardiovascular system, the heptapeptides probably also have a neurohormonal rôle on the Helix aspersa heart itself. The binding affinities of the various antisera used in these studies were examined in competitive RIAs, in non-competitive dot-blot assays or in both.