Achatina cardioexitatory peptide-1 (ACEP-1) is an undecapeptide identified from the African giant snail Achatina fulica. Structurally related peptides are known in a sea hare, Aplysia californica, and a freshwater snail, Lymnaea stagnalis. A G protein-coupled receptor for the ACEP-1 receptor has been identified in several animals.
ACEP-1 was originally isolated from the peptidic extract of the atria of Achatina fulica through the combination of fractionation with reversed-phase or cation-exchange column HPLC and bioassay on the ventricle of the animal.In Aplysia, the L5-67 gene that is specifically expressed in the left upper quadrant (LUQ) neurons of the abdominal ganglia was identified to be a precursor of an ACEP-1 related peptide.The peptide was named LUQIN.In the freshwater snail L. stagnalis, the ACEP-1 related peptide, LyCEP, was purified from the ganglia of the animal as the endogenous ligand to an orphan GPCR, GRL106.
ACEP-1 is an undecapeptide while all the other related peptides are decapeptides. ACEPs identified in mollusks share the identical C-terminal WRPQGRF-NH2 structure.
ACEP-1 and LyCEP have cardioexcitatory action on A. fulica and L. stagnalis, respectively.A major difference in the action of the two peptides is that ACEP-1 augments the beating amplitude of the ventricle but not the auricle of Achatina while LyCEP augments the beating frequency of the auricle of Lymnaea. ACEP-1 increases the phasic contractions of the penis retractor muscle and buccal muscle that were elicited by the electrical stimulation of the muscles.It also induces the spontaneous discharge of buccal B4 neurons. ACEP-1 in the B10 neuron, together with ACh, mediates an excitatory action on the radula protractor muscle.
