title: Barium modifies the concentration dependence of active potassium transport by insect midgut.
abstract: The rate of active K+ transport by the isolated lepidopteran midgut shows a rectangular hyperbolic relation to [K+] over the range 20 to 70 mM K+ in the absence of any divalent cation. Addition of Ba++ to the hemolymph (K+ uptake) side introduces a linear component to the concentration dependence, such that active K+ transport is decreased at [K+] of 55 mM or less, but increased transiently at higher [K+]. As [Ba++] is increased over the range 2 to 8 mM the linear component increases and the saturating component decreases; in 8 mM Ba++ the concentration dependence is dominated by the linear component. The effect of Ba++ cannot easily be accounted for by simple competition with K+ for basal membrane uptake sites. Similar effects might be exercised by other alkali earth cations, since the concentration dependence of active K+ transport possesses a substantial linear component in solutions containing 5 mM Ca++ and 5 mM Mg++ (the alkali earth metal concentrations of standard lepidopteran saline).
mesh_terms: D000818:Animals; D001464:Barium / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D004064:Digestive System / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D007915:Lepidoptera / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D009036:Moths / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*
chemical_list: D001464:Barium; D008274:Magnesium; D011188:Potassium; D002118:Calcium