Fig. 7.

SYWKQCAFNAVSCFamide significantly increase the amplitude, but not the frequency, of spontaneous heartbeat in Homarus americanus. (A) Pooled data from 16 preparations show that SYWKQCAFNAVSCFamide significantly increased the amplitude of heart contractions (t-test, P=0.015). However, it had no consistent effect on heartbeat frequency. (B) The extent of increase was larger in preparations with initially low amplitudes, suggesting that the effect of the peptide is to some extent state dependent. (C) It is probable that the lack of significance for frequency change is due, at least in part, to a state-dependent effect of the peptide, where the rate of heartbeat was increased when the baseline frequency was low, but decreased when baseline rate was high.