Figure 3.

Simulation of the effect of leakage current through the patch microelectrode seal resistance in a cell which expresses a realistic combination of time independent or background currents: (i) a nonlinear K⁺ current, I_K1, (ii) a Na⁺/K⁺ pump current, I_NaK and (iii) a Na⁺ current, I_bNa. (A) shows the current-voltage relations for each of I_K1, I_NaK and I_bNa. (B) shows the patch electrode total current, I_e, as a function of membrane potential, for three different values of seal resistance R_s. Note that for R_s = 30 GΩ there are three zero-current potentials: −77, −36 and −4.5 mV (black dots). For R_s = 8 GΩ, the zero-current membrane potentials are −61 and −2.5 mV. At R_s = 3 GΩ, zero current only occurs when the membrane potential depolarizes to V_m = −1 mV. (C) shows the relationship between V_o and R_s for the three-conductance cell model in (A). For R_s ≥ 8 GΩ, the cell exhibits 3 distinct values of V_o, while for R_s < 8 GΩ, there is only one, very deoplarized value. There is a very sharp “discontinuity” in the V_o-vs.-R_s relation in the vicinity of R_s = 8 G. The dotted line represents the true value of resting potential at −85 mV.