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Journal of Experimental Biology 116,153-167 (1985)
Published by Company of Biologists 1985

Further Observations on the Regulation of KCl ABSORPTION ACROSS LOCUST RECTUM

J. W. HANRAHAN 1 and J. E. PHILLIPS 2

1 Department of Zoology, University of British Columbia, Vancouver, B.C. V6T 2A9, Canada; Department of Physiology, Yale University Medical School, New Haven, Conn. 06510, U.S.A.
2 Department of Zoology, University of British Columbia, Vancouver, B.C. V6T 2A9, Canada

1. Electrophysiological and tracer flux techniques were used to studyregulation of KC1 reabsorption across locust recta. Physiologically high K+levels (100 mmolI-1) on the lumen side stimulated net 36Cl flux and reduced the theoretical energy cost of anion transport under open-circuit conductions.

2. The stimulation of short-circuit current (Ibc i.e. active C- absorption) by crude corpora cardiaca extracts (CC) was not dependent on exogenous Ca2+. Stimulations of Ibc 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 Ibc and caused a disproportionately large increase in Rt, consistent with a decrease in theshunt (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 atthe end of resorptive cycles also inhibited Ibc, apparently without affecting K+ permeability.

Key words: Locust rectum, potassium chloride absorption, regulation, Locust rectum, potassium chloride absorption, regulation

Accepted on September 17, 1984






© The Company of Biologists Ltd 1985