Figure 3. Effect of NPPB and IAA-94 on a 45 mm K⁺ depolarization-induced isometric force.

A, 100 μm NPPB completely blocked a 45 mm K⁺ depolarization-induced isometric force. Micromolar concentrations of NPPB were added cumulatively, to gain a concentration-effect curve for the relaxation of the 45 mm K⁺ depolarization-induced isometric force (means ± s.e.m., n = 5). The passive tension was measured in the presence of 2 μm (-)202-791, a DHP antagonist, at the end of the experiment. Data were fitted to a Hill function giving an IC₅₀ of 10.0 ± 0.76 μm, and a slope of -1.28 ± 0.10. B, 200 μm IAA-94 completely relaxed a 45 mm K⁺depolarization-induced isometric force. The cumulative concentration-effect curve was fitted to a Hill function giving an IC₅₀ of 17.0 ± 1.2 μm and a slope of 0.85 ± 0.04 (means ± s.e.m., n = 4).