Fig. 2
From: The retinal pigment epithelium displays electrical excitability and lateral signal spreading
Kinetics of voltage-activated Na+ currents (INa). A Typical INa; IC, residual capacitive current; IK, the putative voltage-activated K+ current. B Average current-voltage (I–V) relationship for INa (n = 25); here and elsewhere error bars are s.d. (Additional file 2: Table S1). C Steady-state inactivation (SSI) was studied by evoking INa at 0 mV after 50 ms conditioning pre-pulses from −150 to −10 mV. D Voltage dependencies of the average peak INa (circles) and its time to peak (triangles) from SSI experiments (n = 17), and voltage dependence of the normalized peak INa conductance (n = 25, squares). SSI data were divided by the amplitude of INa after the pre-pulse to −150 mV; in the figure, average values were fitted with a sigmoidal equation. Conductance at each membrane potential V was calculated using peak INa from I–V relations as in B and equation gNa(V) = INa/(V − Erev), where ENa = 85.8 mV (Additional file 2: Table S1). E Recovery of INa from inactivation. INa was evoked and inactivated by 50-ms pre-pulses to 0 mV, after which hyperpolarizing pulses of increasing duration ranging from 0.5 to 21.0 ms were applied to recover INa; this was followed by a testing pulse to 0 mV. In these experiments, the holding potential between the trials and the recovery potential were the same. F By plotting peak INa during recovery from inactivation against the hyperpolarizing pulse duration and then fitting the data with a first-order exponential rise-to-maximum equation, recovery time constants (τrec) can be obtained; examples are from the same cell as in E. G Voltage dependence of average recovery time constants (Additional file 2: Table S1)