Figure 6. Low (0.2 mm) but not high concentrations of caffeine reverse the action of 2.0 mm tetracaine in abolishing delayed q_γ charge movements.

A, typical charge movements obtained in the presence of both 0.2 mm caffeine and 2.0 mm tetracaine. B, charge movements from a fibre studied in 5.0 mm caffeine and 2 mm tetracaine. A, fibre Z84 in the presence of both 0.2 mm caffeine and 2 mm tetracaine: temperature = 4.6 °C, R_i = 402.5 Ω cm. Initial cable constants: λ = 1.7 mm, r_i = 10046 kΩ cm⁻¹, d = 71.4 μm, r_m = 273.9 kΩ cm, R_m = 6.15 kΩ cm², C_m = 7.3 μF cm⁻². Final cable constants: λ = 1.7 mm, r_i = 8587 kΩ cm⁻¹, d = 77.3 μm, r_m = 249.8 kΩ cm, R_m = 6.06 kΩ cm², C_m = 8.8 μF cm⁻². B, fibre Z35 studied in 5.0 mm caffeine and 2.0 mm tetracaine: temperature = 5.0 °C, R_i = 379.4 Ω cm. Initial cable constants: λ = 1.8 mm, r_i = 6149.0 kΩ cm⁻¹, d = 90.7 μm, r_m = 203.9 kΩ cm, R_m = 5.82 kΩ cm², C_m = 10.0 μF cm². Final cable constants: λ = 1.6 mm, r_i = 4852.0 kΩ cm⁻¹, d = 102.1 μm, r_m = 120.31 kΩ cm, R_m = 3.86 kΩ cm², C_m = 12.1 μF cm⁻².