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 corticotrop in-releasing factor (CRF)-related diuretic peptide (Acheta-DP) was inv estigated using isolated denervated foreguts from the house cricket, A cheta domesticus. Acheta-DP increased the frequency and amplitude of c ontractions of the foregut at a threshold concentration of 3.74+/-0.00 2 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 c aused a 10-fold increase in cyclic AMP production by isolated foreguts . The ability of IBMX to potentiate the myotropic activity of Acheta-D P suggests the peptide acts via a cyclic AMP-dependent mechanism, In s upport of this, forskolin produced a peptide-like response, and enhanc ed the effect of Acheta-DP. Myotropic activity was dependent on extrac ellular calcium, and was inhibited by the L-type calcium channel antag onist, nifedipine, Bay K 8644 enhanced the response of the foregut to both Acheta-DP and to dibutyryl cyclic AMP, suggesting that the physio logical response arose from calcium influx through L-type calcium chan nels, It is proposed that Acheta-DP binds to a receptor on muscle fibr e membranes activating adenylyl cyclase. The resultant increase in int racellular cyclic AMP is thought to open L-type calcium channels and t hereby stimulate gut contractions. Copyright (C) 1996 Elsevier Science Ltd