Electrical field stimulation-induced response of the rat gastric fundus longitudinal muscle strips after serial administration of atropine, DA-9701, N-nitro-L-arginine (L-NNA), MRS2500 and tetrodotoxin (TTX). (A, B) When atropine was added, peak and nadir did not show significant change (by Wilcoxon signed ranks test). (C, D) When DA-9701 (0.5, 5, 25 and 50 μg) was added in the presence of atropine, peak and nadir did not show significant dose-dependent change (Kruskal Wallis test for testing differences in EFS-induced contractile responses for different DA-9701 doses). (E) Subsequent addition of L-NNA, MRS2500 and TTX in the presence of atropine and DA-9701 (50 μg) did not affect peak (compared with previous value by Wilcoxon signed ranks test). (F) Subsequent addition of L-NNA in the presence of atropine and DA-9701 (50 μg) decreased nadir by inhibiting relaxation, while addition of MRS2500 and TTX in the presence of atropine, DA-9701 (50 μg) and L-NNA did not affect nadir further (*P < 0.05, compared with previous value by Wilcoxon signed ranks test).