Figure 3.

Current families were obtained using a K⁺-free internal Na⁺ solution (A) and, in a different patch, following addition of 10 mM internal K⁺ (B). Holding potential was −80 mV and currents were recorded using on-line −P/n protocols for leak and capacity current subtraction. Test pulse voltages increased by 20-mV increments in A and by 10-mV increments in B. (A) In the absence of internal K⁺ ions, all outward currents are carried by Na⁺ ions. Both peak Na⁺ currents (○) and steady state outward Na⁺ currents (•) increase steeply at potentials greater than +80 mV. Inactivation becomes readily apparent only at the most positive potentials. (B) In the presence of internal K⁺ ions, peak currents (○) increase to a maximum at +10 mV, followed by a region of negative slope conductance between +20 and +70 mV. At potentials greater than +80 mV, peak currents rise steeply again, just as in A. However, end currents fall steadily at potentials greater than +10 mV (•). Symbols are connected by straight lines. Data in A and B were obtained from two different inside-out patches. All traces recorded using 5-s interpulse intervals.