Table 1.
Curve parameters for the concentration–effect curves of the inotropic and lusitropic effects of 5-HT in left atrial pectinate muscles of young pigs
| Administration method | pEC50 | α | nH |
|---|---|---|---|
| Inotropic effect | |||
| Noncumulative | 6.61±0.14 | 85.5±6.5*** | 0.66±0.05 |
| Cumulative | 6.82±0.13### | 52.7±5.4### | 0.86±0.09 |
| Cumulative (IBMX) | 7.71±0.10$$$ | 88.7±5.2 | 0.93±0.07$ |
| Reduction in time to peak force (tpf) | |||
| Noncumulative | 6.38±0.13* | 71.1±6.0* | ND |
| Cumulative | 6.99±0.21 | 50.7±5.4 | ND |
| Cumulative (IBMX) | ND | ND | ND |
| Reduction in time to reach 50% relaxation (t50) | |||
| Noncumulative | 6.40±0.22 | 67.3±8.6 | ND |
| Cumulative | 6.88±0.20 | 58.9±6.0 | ND |
| Cumulative (IBMX) | ND | ND | ND |
The parameters α, pEC50 and nH were obtained from the iterative fitting procedure to the Hill equation; a mixed-effects procedure was used for the inotropic data. nH values for tpf and t50 are not shown since no animal-specific correlation was used in the fitting procedures, which can cause an underestimation of the Hill slope. Experiments were performed in the presence of propranolol (0.2 μM) and cocaine (6 μM), and 5-HT was administered noncumulatively, cumulatively or cumulatively in the presence of 20 μM IBMX. Results were expressed as the percentage increase compared to the response by isoprenaline (0.1 mM). Since the reduction in tpf and t50 by isoprenaline in the presence of IBMX was very small, normalizing the data to isoprenaline was not meaningful and no fitting procedures were performed on these data. The values are expressed as mean±s.e.m.
P<0.05
P<0.001 noncumulative versus cumulative.
P<0.001 cumulative versus cumulative (IBMX).
P<0.05
P<0.001 cumulative (IBMX) versus noncumulative, ND: not determined.