Table 4.
Curve parameters for concentration–effect curves of the left atrial inotropic and the right atrial chronotropic effect in newborn piglets
| Agonist | pEC50 | α | nH |
|---|---|---|---|
| Inotropic effect | |||
| 5-HT (n=7) | 6.54±0.11 | 69.8±6.1 | 0.91±0.07 |
| Prucalopride (n=6/7) | 6.79±0.38 | 30.4±8.0 | 0.91±0.14 |
| Tegaserod (n=5/7) | 7.18±0.20 | 32.7±6.6 | 0.54±0.07 |
| R149402 (n=6/7) | 4.83±0.37 | 56.3±12.2 | 0.37±0.04 |
| R199715 (n=5/6) | 6.19±0.40 | 28.3±6.8 | 0.41±0.07 |
| Chronotropic effect | |||
| 5-HT (n=6) | 6.85±0.12 | 64.3±3.3 | 1.23±0.12 |
| Prucalopride (n=7) | 7.06±0.14 | 14.4±3.5 | 0.85±0.16 |
| Tegaserod (n=10) | 6.49±0.12 | 21.8±2.8 | 0.85±0.09 |
| R149402 (n=4/7) | 8.00±0.14 | 0.8±0.7 | 3.16±1.70 |
| R199715 (n=8/10) | 8.83±0.06 | 10.0±3.3 | 10.58±5.27 |
Inotropic experiments in left atrium were carried out in the presence of cocaine (6 μM), propranolol (0.2 μM) and IBMX (20 μM). In experiments with the spontaneously beating right atrium, propranolol was added to the organ bath in all experiments, while cocaine was only present in experiments with 5-HT. The parameters were obtained using a mixed-effects fitting procedure with the Hill equation. The values are expressed as mean±s.e.m. Only responsive atria were used to obtain curve parameters; the numbers used for fitting versus total number studied are shown within brackets. The inotropic and chronotropic results for R149402 and R199715 are shown in italic; for the inotropic results, the very low Hill slope is indicative for low, inconsistent responses and misleading fits; for the chronotropic results, the high Hill slope results from the fact that the first chronotropically active agonist concentration resulted in a nearly maximal response because of the low response in some animals.