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Journal of Experimental Biology 111,201-223 (1984)
Published by Company of Biologists 1984

KCl Transport Across an Insect Epithelium: Characterization of K-Stimulated Cl Absorption and Active K Transport

J. W. HANRAHAN ¹ and J. E. PHILLIPS ²

¹ Department of Zoology, University of British Columbia, Vancouver, B.C. Canada V6T2A9; Department of Physiology, Yale University School of Medicine, 333 Cedar St, New Haven, Conn. 06510, U.S.A.
² Department of Zoology, University of British Columbia, Vancouver, B.C. Canada V6T2A9

The kinetics of ³⁶C1 fluxes across cAMP-stimulated, short-circuited locust rectum were studied. Raising external K⁺ from 0 to 100 mM increased both K_t and V_max for net Cl transport (J_net^Cl) by four- to six-fold. Hill plots of J_net^Cl indicated non-cooperative Cl interactions. The sequence for cation stimulation of J_net^Cl was K > Rb > Cs > Na > NH₄ . Low levels of K were stimulatory only when added to the mucosal side. Cyclic AMP (cAMP) caused a small active absorption of K, although this was minor compared to the four-fold increase in transepithelial K diffusion (P_K). Neither cAMP stimulation of J_net^K nor of PK was sensitive to Cl removal, suggesting that K-stimulated Cl absorption and K transport are not mediated by the same co-transport mechanism. Potassium is the counter-ion for electrogenic Cl transport because J_net^K was less than 10% of the J_net^K during cAMP exposure under I_sc conditions, but J_net^K equalled J_net^Cl at open-circuit.

Key words: Chloride absorption, K-stimulated Cl transport, cAMP, electrogenic chloride transport

Accepted on February 29, 1984