SKA-31 decreases the spontaneous phasic contractions in a concentration-dependent manner in guinea pig DSM isolated strips. A, representative recordings showing the concentration-response inhibitory effects for SKA-31 (10 nM-10 μM) on the DSM spontaneous phasic contractions. B, representative recordings depicting the concentration-response inhibitory effects for SKA-31 (10 nM-10 μM) on the DSM spontaneous phasic contractions in the presence of apamin (1 μM). C, representative recordings showing the concentration-response effects for SKA-31 (10 nM-10 μM) on the DSM spontaneous phasic contraction in the presence of TRAM-34 (1 μM). SKA-31 was added in increasing concentrations every 10 min to the bath solution. All recordings were performed in the presence of TTX (1 μM). D, concentration-response curves for the inhibitory effects of SKA-31 alone (■) and after preincubation with 1 μM apamin (▾) or 1 μM TRAM-34 (▴). X-axis in D is log transformation of SKA-31 molar concentration. SKA-31 decreased the spontaneous phasic contraction amplitude, muscle force integral, phasic contraction frequency, and duration in a concentration-dependent manner (n = 10; N = 8). Preincubation of DSM isolated strips with 1 μM apamin significantly decreased the inhibitory effects of SKA-31 and caused a significant inhibition of the concentration-response curves (n = 9; N = 8; **, P < 0.01; *, P < 0.05). TRAM-34 (1 μM) did not block the inhibitory effect of SKA-31 (n = 7; N = 7; P > 0.05). Data are means ± S.E.M.