FIG. 6.

Measurement of channel selectivities using voltage ramps. Recombinant MOMPs from C. psittaci (a) and C. trachomatis (b) were subjected to voltage ramps (lower panel) with 250 mM KCl in the cis bilayer chamber and 50 mM KCl in the trans chamber. Positive, upgoing currents at 0 mV (i.e., in the absence of an electrical driving force) indicate a net flux of K⁺ flowing cis to trans (i.e., channels from both species are more selective for K⁺ than for Cl⁻). The reversal (equilibrium) potentials, where negative holding potentials (applied to the cis chamber; see Materials and Methods) exactly balance the chemical driving force, are indicated by arrows.