Rectal acid secretion in the desert locust, Schistocerca gregaria

Abstract

The role played by the rectum in haemolymph pH regulation and the epithelial transport mechanisms involved were investigated in the desert locust ( Schistocerca gregaria) both in vivo and in vitro. Injection-retrieval experiments performed with an in situ ligated rectal preparation demonstrate that the rectal epithelium is capable of generating and maintaining the low pH values observed in the rectum of the intact animal. In vitro experiments in which isolated recta were mounted as flat-sheets in Ussing chambers suggest that the acidification is due to an active H + secretory mechanism rather than selective secretion or reabsorption of either phosphate or bicarbonate. Microelectrode measurements of intracellular pH demonstrate that acid secretion occurs against electrochemical gradients of at least 79 mV at the apical membrane. The level of rectal acidification observed in vivo directly reflected the acid/base status of the animal when locusts were made acidotic by injection with 0.1 N hydrochloric acid. However, contraluminal pH had no effect on rectal acid secretion ( J H) in the in vitro preparation. This suggests that the rectum does have a pH regulatory role, but that it is modulated by some factor(s) other than haemolymph pH per se.