Figure 2

MC3-ISMs have a linear response to [Cl⁻] changes from 0.1 to 100 mM. (A) Continuous record of the response (V_Cl) for an MC3-ISM exposed to solutions of various [Cl⁻] from 0.001 mM to 100 mM, obtained by serial dilutions of a 100 mM NaCl solution with water. (B) Continuous record of another MC3-ISM exposed to the same nominal [Cl⁻], but obtained by mixing Cl-based and SO₄-based solutions (see Methods). The dashed lines in (A,B) represent the steady state values of the ISMs at the indicated [Cl⁻]. (C) The steady-state V_Cl is plotted as a function of a_Cl, which was calculated on the basis of the ionic strength of the test solutions (See Methods). A linear fit of V_Cl as a function of a_Cl over a range from 0.088 to 75 mM, for the dilution method, had a slope of 52.8 ± 0.63 mV/decade (n = 4, straight line).