Fig. 3. Effects of bumetanide on basolateral membrane potential, transepithelial potential (TEP), intracellular pH and lumen pH in 10^–6 mol l^–1 5-HT stimulated Malpighian tubules. Representative simultaneous recordings of TEP (A), lumen pH (B), basolateral membrane potential (V_bl) (D) and intracellular pH (E). Downward-pointing arrows indicate impalement of the cell or lumen and upward-pointing arrows indicate the removal of the microelectrode from the cell or lumen. Tubules were exposed to 10^–5 mol l^–1 bumetanide for the period indicated by the horizontal bar. Values are means ± s.e.m. for lumen pH (C, N=7) and intracellular pH (F, N=4) before and after bumetanide treatment. The asterisk indicates a significant difference (P<0.05, Student's t-test) between control and experimental values (means + s.e.m.).