Neuropeptide Control of Ion and Fluid Transport Across Locust Hindgut

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Abstract
The anterior (ileum) and posterior (rectum) segments of locust hindgut constitute the reabsorptive part of the locust excretory system. They are functionally analogous to the proximal convoluted tubule and more distal parts, respectively, of the mammalian kidney tubule. Transport mechanisms are well understood in the rectum, and an epithelial model has been proposed. Electrogenic active absorption of Cl− at the apical membrane drives K+ transport (electrical coupling) and hence fluid transport (Jv). A partially purified neuropeptide (CTSH) from the Corpus Cardiacum (CC) stimulates KC1 transport, and therefore presumably fluid absorption via cAMP as second messenger. Another neuropeptide (purified and sequenced) from locust CC, neuroparsins, is reported to stimulate rectal Jv via the inositol triphosphate (Ca2+) system, but actions on ion transport processes are unknown There is considerable similarity of transport processes in locust ileum and rectum. A neuropeptide (ITP) acting on the ileum has been purified and partially sequenced from locust CC (storage lobe). ITP has high sequence homology with a family of crustacean neuropeptides. ITP, apparently acting via cAMP, stimulates ileal reabsorption of Cl−, K+, Na+ and fluid by several-fold. It also inhibits active H+ secretion in the ileum, a process involved in hemolymph acid-base regulation. ITP has negligibleeffects on rectal transport processes. Thus separate neuropeptides apparently control transportevents in locust ileum and rectum.

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