Fig. 2. Effects of 10^–4 mol l^–1 bumetanide on (A) fluid secretion, (B) K⁺ flux and (C) Na⁺ flux for tubules after exposure to ouabain. After exposure to 10^–4 mol l^–1 ouabain for 30 min, bumetanide was added to Malpighian tubules in the experimental group (filled bars) and the vehicle (0.1% ethanol) was added to the control group (open bars). Data are expressed as mean ± S.E.M. Asterisks indicate significant differences between flux before and after addition of bumetanide (paired t-test, P<0.05, N=11).