Fig. 4.
Both heartbeat frequency and contraction amplitude in the whole heart preparation changed in a dose-dependent manner in the presence of myosuppressin. Pooled data from preparations exposed to concentrations of myosuppressin ranging from 10−6 to 10−9 mol l−1 showed that heart rate decreased (A) and contraction amplitude increased (B), with larger effects at higher concentrations. Threshold for cycle frequency, defined as the concentration needed to produce a change significantly different from zero, was between 10−8 and 10−9 mol l−1; threshold for changes in amplitude was between 10−7 and 10−8 mol l−1. *Significantly different from zero, one-sample, two-tailed t-test, P<0.05. N=6, 6, 11, 14 for 10−9, 10−8, 10−7 and 10−6 mol l−1 myosuppressin applications. Error bars represent standard errors.