Fig. 1.

Barium applied to the basolateral membrane of the Drosophila melanogaster renal tubule decreases transepithelial potential difference and transepithelial K⁺ flux. A: transepithelial potential difference was measured in isolated perfused wild-type tubules (wBerlin, n = 4) at baseline, after the application of peritubular 2 mM barium, and after washout. Transepithelial potential difference was reversibly decreased after barium administration. The time to initial effect after changing the bath to the barium-containing bath was 4 ± 1 min. The time to maximal effect after changing the bath to the barium-containing bath was 11 ± 2 min. There was no signification difference between “before” and “recovery” transepithelial potentials. B: transepithelial K⁺ flux (pmol/min per tubule) was measured in wild-type (wBerlin) tubules using the Ramsay assay and ion-specific electrodes. K⁺ flux was measured for 1 h before drug addition (baseline) and in the same tubules for 1 h after the addition of 2 mM barium or vehicle (n = 7–8 tubules/condition). There was an increase in K⁺ flux after vehicle addition, whereas the addition of barium resulted in a decrease in K⁺ flux. All values shown in this and subsequent figures are means ± SE. *P < 0.05, ***P < 0.001.