Fig. 3. The sigmoid concentration-response curves of BRL₃₇₃₄₄-mediated inhibition on V_S of BRL₃₇₃₄₄ alone (0.1-100 nmol l^-1) and of BRL ₃₇₃₄₄ plus a single concentration of SR₅₉₂₃₀ (10 nmol l^-1) on the isolated and perfused working eel heart preparation. Inhibition of contractility is expressed as a percentage of V_S [baseline=0%, peak inhibition by BRL₃₇₃₄₄ and BRL₃₇₃₄₄ plus SR₅₉₂₃₀= -100%]. The EC₅₀ values (in log mol l^-1) of BRL₃₇₃₄₄ alone was -7.68±0,12 (r²=0.98), of BRL ₃₇₃₄₄ plus SR₅₉₂₃₀ (10 nmol l^-1) was -6.6±0.55 (r²=0.96). Comparison between groups (two-way ANOVA, Duncan's test); P<0.05 (N=8).