Abstract
ABSTRACT The kinetics of 36C1 fluxes across cAMP-stimulated, short-circuited locust rectum were studied. Raising external K+ from 0 to 100 mM increased both Kt and Vmax for net Cl transport by four- to six-fold. Hill plots of indicated non-cooperative Cl interactions. The sequence for cation stimulation of 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 fourfold increase in transepithelial K diffusion (PK ). Neither cAMP stimulation of 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 was less than 10% of the during cAMP exposure under Isc conditions, but equalled at open-circuit.
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