Figure 4.

Time course of hypoxia in left atrial preparations. (A–C) The force of contraction in% of control (Ctr = initial force at the beginning of the experiment) during the time of oxygenation and hypoxia is presented. After the addition of serotonin (5-HT, 1 μM, protocol I), the relative force was greatly increased in 5-HT₄-TG and reached initial values again after hypoxia and reoxygenation (A). Preconditioning (protocol IV) as short hypoxia for 10 min was not beneficial (B). Under the condition of single hypoxia (protocol II), force decline was faster in TG left atria than in WT (C). WT = wild-type mice, 5-HT₄-TG=5-HT₄-transgenic mice. Data shown are means ± SEM. * p < 0.05 vs. WT.