Figure 3. Similar I_Ca in Epi and Endo cells.

A, current–voltage relationship of I_Ca in Epi and Endo cells. Representative I_Ca traces are shown to the right (inset). B, I_Ca steady-state inactivation is shown as a plot of normalized peak current (I/I_max) as a function of conditioning potential. For the voltage dependence of activation, peak I_Ca currents at test potentials between −50 and +10 mV were converted into conductances (G = I_Ca/[test pulse potential – reversal potential of I_Ca]), normalized (G/G_max), and plotted as a function of test potential. Smooth lines represent best-fit curves to the data determined by a least-squares method using a Boltzmann equation, y = [(A₁− A₂)/1 + e(^V–V_1/2/k)], where A₁, A₂, V_1/2, and k are the initial value, final value, the voltage at which 50% of the current or conductance was observed, and the slope factor. For the steady-state inactivation of I_Ca in Epi cells A₁ = 1, A₂ = 0, V_1/2 = −25 mV and k = 5. For the steady-state inactivation of I_Ca in Endo cells A₁ = 1, A₂ = 0, V_1/2 = −24 mV and k = 6. For the conductance–voltage relationship of I_Ca in Epi cells A₁ = 0, A₂ = 1, V_1/2 = −19 mV and k = 5. For the conductance–voltage relationship of I_Ca in Endo cells A₁ = 0, A₂ = 1, V_1/2 = −16 mV and k = 5. C, summary of the parameters used to fit the conductance and steady-state inactivation relationships of I_Ca in Epi and Endo cells. *P < 0.05.