Fig. 3.

Bufotenin increases contractility in atrial preparations of mice overexpressing 5-HT₄ receptors. A Representative original recordings of a concentration response curve for bufotenin in an isolated electrically stimulated (1 Hz) left atrial preparation from 5-HT₄-TG and for comparison from WT. B Concentration-dependent positive inotropic effect of bufotenin in isolated electrically stimulated (1 Hz) atrial preparations from 5-HT₄-TG (circles). There were no effects of bufotenine in WT preparations (squares). Basal force of contraction amounted to 2.82 ± 0.42 mN. C Concentration-dependent effect of bufotenin on time to peak tension (TTP) and D on time of relaxation (TR) in isolated electrically stimulated (1 Hz) atrial preparations from 5-HT₄-TG (circles) and WT (squares). Basal TTP amounted to 14.86 ± 0.31 ms and basal TR amounted to 31.18 ± 1.77 ms. E Concentration-dependent effect of bufotenin on maximum and F minimum rate of tension development (dF/dt max and min) in isolated electrically stimulated (1 Hz) atrial preparations from 5-HT₄-TG (circles) and WT (squares). Basal maximum rate of tension development amounted to 174.3 ± 31.87 mN/s and basal minimum rate of tension development amounted to − 99.2 ± 16.31 mN/s. G Concentration-dependent chronotropic effect of bufotenin in isolated spontaneously beating atrial preparations from 5-HT₄-TG (circles) and WT (squares). Basal rate of contraction amounted to 310 ± 22 beats per minute. *Indicates the first significant difference versus control (Ctr = before drugs addition), #indicates the first significant difference versus 5-HT₄-TG. Numbers in brackets = number of experiments