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Insect midgut K⁺ secretion: concerted run-down of apical/basolateral transporters with extra-/intracellular acidity

Wolfgang Zeiske^*, Heiko Meyer and Helmut Wieczorek

Department of Biology/Chemistry, Division of Animal Physiology, University of Osnabrück, 49069 Osnabrück, Germany

View larger version (19K): [in a new window]   Fig. 1. (A) Effects of apical and basolateral pH shifts on the transepithelial secretory (positive sign) K+ current. K32, standard saline (see Materials and methods); a, apical variations; b, basolateral variations. (B) Reduction in active K+ transport induced by 5 mmol l–1 basolateral Ba2+ and basolateral/apical acidification in the absence of Ba2+.

View larger version (17K): [in a new window]   Fig. 2. Percentage of the control (pH 8) K+ current (IK) after external acidification on the apical or the basolateral side. Values are shown as means + standard error of the mean (S.E.M.; N=6).

View larger version (7K): [in a new window]   Fig. 3. The effect of 20 mmol l–1 ammonium chloride, replacing sucrose iso-osmotically on the apical (a) or basolateral (b) side, on K+ current. K32, standard saline (see Materials and methods).

View larger version (13K): [in a new window]   Fig. 4. (A) The effect of 10 mmol l–1 sodium propionate (Prop) applied first apically (a) then basolaterally (b), on K+ current. K32, standard saline (see Materials and methods). (B) Percentage of control K+ current (IK) before and after treatment with 20 mmol l–1 basolateral ammonium chloride (left side, N=4) and before and after 10 mmol l–1 apical or basolateral propionate (Prop) (right side, N=4). Values are means + S.E.M.

View larger version (15K): [in a new window]   Fig. 5. (A) The effect of apical (a) or basolateral (b) sodium azide on K+ current. K32, standard saline (see Materials and methods). Azide concentrations are given in mmol l–1. (B) Percentage of control K+ current (IK) after apical or basolateral addition of 1 or 10 mmol l–1 sodium azide. Values are means + S.E.M. (N=4).

View larger version (9K): [in a new window]   Fig. 6. Inhibition of K+ current induced by basolateral acidification before and after basolateral membrane permeabilisation using nystatin. K32, standard saline (see Materials and methods); a, apical variations; b, basolateral variations.

View larger version (14K): [in a new window]   Fig. 7. (A) Establishment of a reversed (negative sign) current (abbreviated as IKrev in the text) after apical (a) permeabilisation with nystatin and its inhibition by apical or basolateral (b) acidification. K32, standard saline (see Materials and methods); Na32, all K+ in the saline replaced by Na+. (B) Percentage of control pump current (IP, left side, N=4) and reversed current (IKrev, right side, N=4) following intracellular acidification via basolateral (left side) or apical (right side) nystatin channels. Values are means + S.E.M.

View larger version (10K): [in a new window]   Fig. 8. Establishment of a reversed (negative sign) current (abbreviated as IKrev in the text) after apical (a) permeabilisation with nystatin, and the effect of 1 mmol l–1 sodium azide in K+-free basolateral (b) saline at different cell pH values. K32, standard saline (see Materials and methods); Na32, all K+ in the saline replaced by Na+.