Further Observations on the Regulation of KCl Absorption Across Locust Rectum Available to Purchase

Electrophysiological and tracer flux techniques were used to study regulation of KCl reabsorption across locust recta. Physiologically high K⁺ levels (100 mmol 1⁻¹) on the lumen side stimulated net ³⁶C1 flux and reduced the theoretical energy cost of anion transport under open-circuit conductions.

The stimulation of short-circuit current (I_SC, i.e. active Cl⁻ absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca²⁺. Stimulations of I_sc 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 (R_t), suggesting that chloride transport stimulating hormone (CTSH) regulates both active Cl⁻ absorption and counter-ion (K⁺) permeability.

High mucosal osmolarity or K⁺ concentration decreased I_sc. and caused a disproportionately large increase in R_t, 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_sc, apparently without affecting K⁺ permeability.