Figure 11.

TTX-R sodium current use dependence elicited by action potential waveforms. A, top, Single action potentials recorded from two DRG neurons applied as voltage commands at 1 Hz, from a holding potential of -60 or -70 mV. Solid line, Short-duration action potential recorded with internal solution containing the following (in mm): 140 K-methanesulfonate, 13.5 NaCl, 1.6 MgCl₂, 0.09 EGTA, 9 HEPES, 0.9 glucose, 14 Tris-creatine PO₄, 4 MgATP, and 0.3 Tris-GTP, pH 7.4. Dashed line, Long-duration action potential recorded with the same internal solution as above, with 140 mm K-aspartate replacing K-methanesulfonate. In both cases, the external solution was Tyrode's solution. A, Bottom, Peak inward current elicited during action potential waveforms (applied in the same cell), was normalized to the initial value and plotted against sweep number. Filled triangles, The degree of TTX-R sodium current use dependence in this cell during 30 msec steps to 0 mV, applied at 1 Hz from a holding potential of -60 mV. The internal solution contained the following (in mm): 140 K-aspartate, 13.5 NaCl, 1.6 MgCl₂, 0.09 EGTA, 9 HEPES, 14 Tris-creatine PO₄, 4 MgATP, and 0.3 Tris-GTP, pH 7.4. The external solution contained the following (in mm): 150 NaCl, 4 KCl, 2 CaCl₂, 2 MgCl₂, 10 HEPES, 10 glucose, and 5 TEA-Cl, pH 7.4 with 300 nm TTX.