f = a+ g1/(1+exp((x-V1/21)/k1)) + g2/(1+exp(-(x-V1/22)/k2))
where x is the pre-pulse potential, V1/2is the mid-point potential and k is the corresponding slope factor for single Boltzmann functions. Double Boltzmann fits were used to describe the shape of the curve, not to imply the existence of separate channel populations. Numbers 1 and 2 simply indicate first and second mid-points; a along with g are fitting parameters.
Activation curves were obtained from the I-V curves by dividing the peak current at each depolarizing step by the driving force according to the equation: G= I/(Vmem- Erev) , where I is the peak current, Vmem is the membrane potential and Erev is the reversal potential. The conductance (G) was normalized against the maximum conductance (Gmax). For total and the different subtypes of Ca2+For Na+max). Activation and SSI curves were fitted with the Boltzmann equation.