Figure 3.

Hypoxia in atrial preparations. (A) The scheme demonstrates the experimental protocols of the experiments. Paced left atrial preparations from wild-type mice (WT), or 5-HT₄-transgenic mice (5-HT₄-TG) were allowed to equilibrate in the organ bath in buffer saturated with carbogen (=oxygenation, 5% CO₂ and 95% O₂). Then as indicated, four protocols were performed: (I.) 28 min of oxygenation followed by addition of serotonin (5-HT, 1 µM) for 2 min; (II.) 30 min of oxygenation; (III.) 28 min of oxygenation followed by addition of the 5-HT₄-antagonist GR 113808 (GR, 1 µM) for 2 min; (IV.) 10 min of hypoxia (Hyp) followed by 20 min of oxygenation. Thereafter, all conditions (I.–IV.) include the same procedure: 30 min of hypoxia (5% CO₂ and 95% N₂) and then again carbogen (reoxygenation). (B) During hypoxia, left atrial preparations lose their ability to completely relax, and an increase in diastolic tension (contractures) occurs. Under the setups serotonin (1 µM), single hypoxia and GR 113808 (1 µM), 5-HT₄-TG atria developed contractures earlier than WT atria. Roman numbers indicate the experimental protocol, and numbers at the bottom of the columns indicate the number of experiments. Data shown are means ± SEM. * p < 0.05 vs. WT.