Effect of increasing concentrations of carteolol and xamoterol on isometric contraction parameters of guinea pig spontaneously beating atria: comparison with isoprenaline
Isometric contraction curves were analyzed for t1 (time to peak force), t2 (relaxation time), S1 (mean velocity of force development, Fc/t1), and S2 (mean velocity of relaxation, Fc/t2) values, according to Reiter (1974). Experimental conditions are described under Materials and Methods. Results are means ± S.E.M. from seven independent experiments carried out on different myocardial preparations.
Drug | t1 Value | t2 Value | S1 Value | S2 Value | ||
|---|---|---|---|---|---|---|
| ms | mg/ms | |||||
| None | 126.6 ± 4.9 | 246.3 ± 18.7 | 6.0 ± 0.5 | 3.3 ± 0.2 | ||
| Carteolol (0.1 μm) | 125.0 ± 2.9 | 250.0 ± 6.3 | 5.6 ± 1.0 | 2.8 ± 0.5 | ||
| Carteolol (1 μm) | 115.0 ± 7.6 | 226.6 ± 12.0 | 7.4 ± 0.3* | 3.8 ± 0.2 | ||
| Carteolol (10 μm) | 117.5 ± 3.2 | 215.0 ± 18.1 | 7.7 ± 0.5** | 3.9 ± 0.3 | ||
| None | 117.5 ± 2.5 | 228.2 ± 6.9 | 5.2 ± 0.4 | 3.2 ± 0.4 | ||
| Xamoterol (0.01 μm) | 108.7 ± 2.5* | 216.2 ± 4.8 | 6.1 ± 0.5 | 3.2 ± 0.4 | ||
| Xamoterol (0.1 μm) | 107.5 ± 2.8* | 218.1 ± 6.4 | 8.8 ± 0.9* | 5.7 ± 0.3*** | ||
| Xamoterol (1 μm) | 102.5 ± 2.9** | 220.0 ± 8.5 | 11.4 ± 1.2*** | 7.1 ± 0.3*** | ||
| None | 121.2 ± 2.5 | 228.7 ± 5.5 | 6.2 ± 0.5 | 3.6 ± 0.4 | ||
| Isoprenaline (2 μm) | 96.2 ± 3.7*** | 201.2 ± 6.9* | 15.9 ± 1.9*** | 7.7 ± 1.1** | ||
↵* P < 0.05; ** P < 0.01; *** P < 0.001 vs. respective control values.