Figure 2. Strength–duration curves in skinned EDL fibres in various conditions.

A, mean (±s.e.m.) threshold field strength for pulses of indicated width in fibres with Cl⁻ present (•) or absent (^); n = 6 in both cases, with fibres dissected alternately from contralateral muscles bathed with or without Cl⁻. B, threshold field strength data for fibres with Cl⁻ present, before (•) and after (^) addition of 100 μm 9-AC (n = 4). C, similar data with Cl⁻ present in fibres obtained from muscles pre-treated with 100 nm phorbol 12,13-dibutyrate, before (▵) and after (∇) addition of 100 μm 9-AC (n = 5). Where Cl⁻ was present the intracellular bathing solution contained 3 mm Cl⁻. In many instances the error bar is smaller than the symbol. Curves show the least-squares fits of eqn (1). R is in V cm⁻¹ and σ in ms, respectively. A, 3 mm Cl⁻: 15.2 ± 4.0 and 1.66 ± 0.54 (r²= 0.989); 0 mm Cl⁻: 6.3 ± 4.4 and 3.17 ± 2.49 (r²= 0.986). B, 3 mm Cl⁻: 16.4 ± 1.1 and 1.18 ± 0.13 (r²= 0.999); 3 mm Cl⁻+ 100 μm 9-AC: 10.6 ± 1.0 and 1.39 ± 0.21 (r²= 0.998). C, 12.0 ± 2.1 and 1.24 ± 0.28 (r²= 0.994).