Figure 5.

Ba²⁺ identifies augmentation at normal quantal content. A, B, Normalized EPP amplitudes are presented during (A) and after (B) conditioning trains for experiments with both 2 mm Ca²⁺ plus 2 mm Ba²⁺ (open circles) and 2 mm Ca²⁺ alone (filled circles). A clear augmentation component with Ba²⁺ was observed (continuous line, with τ_A = 8.9 ± 1.2 sec, A₀ = 1.8 ± 0.3; τ_D2 = 163 ± 22 sec, D2₀ = 0.32 ± 0.02). C, D, The enhancing effect of Ba²⁺ on augmentation was reversible. Normalized EPP amplitudes are shown during (C) and after (D) conditioning trains from a single experiment with 2 mm added Ba²⁺ (1), after washing out the Ba²⁺ (2), and after adding the Ba²⁺ again (3). The components after the train in part D: 1, τ_A = 15.5 ± 1.2 sec, A₀ = 3.2 ± 1.2, τ_D1 = 2.0 ± 0.9 sec, D1₀ = 0.14 ± 0.08, τ_D2 = 45.8 ± 12.9 sec, D2₀ = 0.44 ± 0.21; 2, τ_A 15.6 ± 1.4 sec, A₀ = 2.3 ± 0.3, τ_D1 = 27.8 ± 3.2 sec, D1₀ = 0.79 ± 0.02; and 3, τ_A = 11.3 ± 1.6 sec, A₀ = 2.4 ± 0.5, τ_D1 = 4.30 ± 3.0 sec, D1₀ = 0.10 ± 0.05, τ_D2 = 1240 ± 1150 sec, D2₀ = 0.44 ± 0.21. E, F, The time constants (filled circles) and magnitudes (open circles) for augmentation and the slow component of depression in six experiments with 2 mm Ca²⁺ plus 2 mm added Ba²⁺.