Characteristics of the positive chronotropic and inotropic effects caused by carteolol and xamoterol in spontaneously beating atria
pD2 is the negative log of the molar concentration of agonist that produced 50% of the maximum effect [i.e., –log EC50 (M)]. Intrinsic activity (α) was calculated as the fraction of the maximum effect of the drugs compared with the maximal response (Emax) caused by isoprenaline in the same preparation. The values were obtained as explained in details under Materials and Methods. The results are presented as means ± S.E.M. and were obtained from seven experiments carried out on different myocardial preparations.
Drugs | Positive Chronotropic Effect | Positive Inotropic Effect | ||||
|---|---|---|---|---|---|---|
| Potency (pD2) | Intrinsic Activity (α) | Potency (pD2) | Intrinsic Activity (α) | |||
| Carteolol | 6.14 ± 0.12 | 0.30 ± 0.03 | 6.30 ± 0.11 | 0.26 ± 0.04 | ||
| Xamoterol | 7.41 ± 0.20a | 0.64 ± 0.04a | 7.18 ± 0.14a | 0.74 ± 0.10a | ||
↵ a P < 0.001 vs. carteolol.