Myotropic activity of Acheta diuretic peptide on the foregut of the house cricket, Acheta domesticus (L)

The myotropic activity and mode of action of an endogenous corticotropin-releasing factor (CRF)-related diuretic peptide (Acheta-DP) was investigated using isolated denervated foreguts from the house cricket, Acheta domesticus. Acheta-DP increased the frequency and amplitude of contractions of the foregut at a threshold concentration of 3.74+/-0.002 nM. The response to the peptide was unaffected by tetrodotoxin (TTX), and is likely to be a direct action on the muscle cells. Acheta-DP caused a 10-fold increase in cyclic AMP production by isolated foreguts. The ability of IBMX to potentiate the myotropic activity of Acheta-DP suggests the peptide acts via a cyclic AMP-dependent mechanism, In support of this, forskolin produced a peptide-like response, and enhanced the effect of Acheta-DP. Myotropic activity was dependent on extracellular calcium, and was inhibited by the L-type calcium channel antagonist, nifedipine, Bay K 8644 enhanced the response of the foregut to both Acheta-DP and to dibutyryl cyclic AMP, suggesting that the physiological response arose from calcium influx through L-type calcium channels, It is proposed that Acheta-DP binds to a receptor on muscle fibre membranes activating adenylyl cyclase. The resultant increase in intracellular cyclic AMP is thought to open L-type calcium channels and thereby stimulate gut contractions. Copyright (C) 1996 Elsevier Science Ltd