Figure 3. Representative tracing of the influence of extracellular Ca²⁺ concentration on IF.

Human bronchi rings were placed in 2.39 mM Ca²⁺ buffer and the tension was set to 4.9 mN (0.5 g). After 1 hour equilibration, the buffer was rapidly replaced by 0 CaPSS resulting in rapid relaxation; this was maintained for at least 30 min at which time Ca²⁺ was sequentially added by substitution with buffer containing 0.1, 0.25, 0.5, 1.0, 2.5, 5.0 or 10.0 mM Ca²⁺. Each concentration was maintained for 20 min to attain a stable force level. Observe the graded contraction produced at each sequential Ca²⁺ addition (n = 3).