Further Observations on the Regulation of Kc1 Absorption across Locust Rectum

1. Electrophysiological and tracer flux techniques were used to study regulation of KC1 reabsorption across locust recta. Physiologically high K levels (100 mmol I") on the lumen side stimulated net Cl flux and reduced the theoretical energy cost of anion transport under open-circuit conductions. 2. The stimulation of short-circuit current (I^, i.e. active C\~ absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca. Stimulations of I^ were greatly enhanced in the presence of theophylline, indicating that the rate of synthesis of cAMP is increased by CC extracts. High CC levels lowered transepithelial resistance (Rt), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl~ absorption and counter-ion (K) permeability. 3. High mucosal osmolarity or K concentration decreased I,,, and caused a disproportionately large increase in Rt, consistent with a decrease in the shunt (K) conductance. Measurements of relative mucosal-to-serosal membrane resistance confirmed that high mucosal K levels reduced apical membrane conductance. Lowering mucosal pH to values observed in vivo at the end of resorptive cycles also inhibited I,,-, apparently without affecting K permeability.