Structure and function of the molluscan myoactive tetradecapeptides

Area of Science:

• * Neurobiology and Pharmacology
• * Molluscan Physiology

Background:

• * Myoactive peptides are crucial for regulating muscle and neuronal activity in invertebrates.
• * Specific peptides like Achatina excitatory peptide 2 (AEP2), Achatina excitatory peptide 3 (AEP3), and Fusinus excitatory peptide 4 (FEP4) are known to affect muscle contractions.

Purpose of the Study:

• * To investigate the effects of AEP2, AEP3, and FEP4 on selected molluscan muscles and neurons.
• * To determine the relative potencies of these peptides in different muscle types.
• * To elucidate the mechanism of action, particularly concerning cholinergic transmission.

Main Methods:

• * Electrophysiological recordings and muscle tension measurements were performed.
• * Experiments utilized penis retractor and radula retractor muscles of *Achatina fulica* (pulmonate gastropod).
• * Radula protractor and retractor muscles of *Fusinus ferrugineus* (prosobranch gastropod) were also studied, along with buccal ganglionic neuron B4.

Main Results:

• * All three peptides (AEP2, AEP3, FEP4) enhanced tetanic contractions in *Achatina fulica* muscles, with potency order AEP2 > AEP3 > FEP4.
• * FEP4 was most potent in enhancing contractions in *Fusinus ferrugineus* muscles, with greater effect on the protractor than the retractor.
• * AEP2 induced rhythmic activity in the cholinergic motoneuron B4 of *Achatina fulica*.

Conclusions:

• * Myoactive tetradecapeptides significantly influence muscle contractility in mollusks.
• * The studied peptides, particularly AEP2 and FEP4, demonstrate differential potency across species and muscle types.
• * Evidence suggests these peptides primarily modulate cholinergic transmission in molluscan neuromuscular systems.