Fig. 4. Hanes–Woolf plots (concentration of amiloride, c_Ami, versus ratio of c_Ami to the induced change in I_sc as a percentage of the control current, E_Ami) of the influence of external amiloride on the currents across split gill lamellae at a clamp voltage of 50 mV (circles; mean 100 % control current=3635±475 µA cm^–2) and on the currents across isolated cuticles at clamp voltages of 50 mV (squares; mean 100 % I_cut=28 530±4889 µA cm^–2) or 10 mV (triangles; mean 100 % I_cut=4782±910 µA cm^–2). I_cut, cuticular current. The lines correspond to linear regressions (r²>0.99 in all cases) over the entire amiloride concentration range used (1.25–200 µmol l^–1 for split gill lamellae and 0.5–100 µmol l^–1 for isolated cuticles). Values are means ± S.E.M. (N=5 in all cases).