Fig. 2. Single and combined effects of barium (Ba; 5 mmol l^–1) and bumetanide (Bu; 100 µmol l^–1) on transepithelial ion secretion in isolated Malpighian tubules of the yellow fever mosquito. After the usual initial 30 min control period, fluid secreted by the tubules was removed for analysis with an electron microprobe, and barium and/or bumetanide was added to the peritubular Ringer solution. Fluid secreted under experimental conditions was collected at the end of the experiment, 25–70 min after introducing the agent of interest to the peritubular Ringer bath. Data are expressed as % of control. N=7 for C and Ba; N=6 for Bu and Ba+Bu. For numeric data, see Table 1. Asterisks indicate significant differences (P<0.05). Effects of bumetanide alone are previously published data (Hegarty et al., 1991).