Figure 1. Effects of SNP on standard longitudinal smooth muscle preparations of opossum oesophagus.

A, single concentration-response curve demonstrating concentration-dependent SNP-induced contraction. Curve was fitted with a Hill equation, which yielded EC₅₀= 239.6± 78.2 μm (n = 10). B, histogram of effects of niflumic acid (NA, 300 μm), 9-AC (1 mm) and nifedipine (Nif, 1 μm) on the contraction produced by SNP (300 μm). Niflumic acid, 9-AC and nifedipine abolished the SNP-induced contraction (n = 7). However, in the presence of niflumic acid (300 μm) application of 60 mm KCl produced contraction to 82.7 ± 8.7 % of control induced by 60 mm KCl (n = 3), suggesting that inhibition of SNP-induced contraction was not due to the non-specific actions of niflumic acid on L-type Ca²⁺ channels or contractile protein processes. *P < 0.05.