9317784 Harrison Regulation of pH is one of the most critical aspects of organismal homeostasis. Although acid-base status affects a wide variety of cellular processes, including enzyme catalysis, ionic balance, membrane transport, and hormone-receptor interactions, our knowledge of this aspect of insect physiology is quite limited. Previous research by Dr. Harrison has shown that locusts regulate extracellular pH quite closely, and that acid- base loads resulting from diet, starvation, or injections of HCl are excreted. A major goal of the proposed research is to determine the specific region(s) of the alimentary canal/hindgut complex responsible for the regulated excretion of acid-base loads. This research will also test whether changes in the secretion of acid-base by the midgut can be directly induced by changes in acid-base status. It is generally assumed (in insects and mammals) that excretion of ammonium is functionally equivalent to acid excretion. However, this assumption has never been tested directly in insects, and recently has been extensively debated for mammals. The proposed study will test whether ammonium excretion by the hindgut of locusts is functionally equivalent to acid secretion in a simple, direct manner. Together, these experiments will provide the first organismal model of the most important mechanisms of long-term acid-base regulation in insects. ***
