Isometric twitch-tension parameters at basal conditions (30°C, 2 mM [Ca2+]out, 1-Hz stimulation rate) and in the presence of 10−6 M isoproterenol or high extracellular calcium (8 mM [Ca2+]out).
| Parameter | Atrial trabeculae | Ventricular trabeculae | ||||
| Basal conditions | WT (n = 12) | R4496C (n = 10) | P value | WT (n = 12) | R4496C (n = 11) | P value |
| Peak tension (mN/mm2) | 11.3 ± 1.3 | 12.9 ± 2.4 | NS | 26.0 ± 4.4 | 26.8 ± 4.5 | NS |
| Time to peak (ms) | 44.9 ± 2.4 | 44.7 ± 1.7 | NS | 63.4 ± 4.2 | 64.9 ± 3.7 | NS |
| Time to 50% relaxation (ms) | 24.1 ± 1.1 | 24.8 ± 2.2 | NS | 42.3 ± 1.7 | 46.1 ± 1.8 | NS |
| Isoproterenol | ||||||
| Peak tension (mN/mm2) | 49.3 ± 8.3 | 22.9 ± 6.4 | <0.01 | 66.3 ± 12.4 | 41.8 ± 8.5 | <0.05 |
| Time to peak (ms) | 39.3 ± 4.4 | 37.7 ± 3.7 | NS | 43.7 ± 3.6 | 44.9 ± 3.7 | NS |
| Time to 50% relaxation (ms) | 17.5 ± 2.1 | 18.1 ± 2.2 | NS | 22.3 ± 1.9 | 23.1 ± 1.8 | NS |
| High extracellular calcium | ||||||
| Peak tension (mN/mm2) | 47.2 ± 8.6 | 25.2 ± 5.6 | <0.05 | 65.4 ± 12.2 | 49.1 ± 9.0 | <0.05 |
| Time to peak (ms) | 47.6 ± 3.3 | 48.4 ± 2.6 | NS | 64.1 ± 3.6 | 64.5 ± 4.1 | NS |
| Time to 50% relaxation (ms) | 25.8 ± 2.7 | 27.1 ± 3.1 | NS | 45.3 ± 4.8 | 46.5 ± 2.3 | NS |
| Parameter | Atrial trabeculae | Ventricular trabeculae | ||||
| Basal conditions | WT (n = 12) | R4496C (n = 10) | P value | WT (n = 12) | R4496C (n = 11) | P value |
| Peak tension (mN/mm2) | 11.3 ± 1.3 | 12.9 ± 2.4 | NS | 26.0 ± 4.4 | 26.8 ± 4.5 | NS |
| Time to peak (ms) | 44.9 ± 2.4 | 44.7 ± 1.7 | NS | 63.4 ± 4.2 | 64.9 ± 3.7 | NS |
| Time to 50% relaxation (ms) | 24.1 ± 1.1 | 24.8 ± 2.2 | NS | 42.3 ± 1.7 | 46.1 ± 1.8 | NS |
| Isoproterenol | ||||||
| Peak tension (mN/mm2) | 49.3 ± 8.3 | 22.9 ± 6.4 | <0.01 | 66.3 ± 12.4 | 41.8 ± 8.5 | <0.05 |
| Time to peak (ms) | 39.3 ± 4.4 | 37.7 ± 3.7 | NS | 43.7 ± 3.6 | 44.9 ± 3.7 | NS |
| Time to 50% relaxation (ms) | 17.5 ± 2.1 | 18.1 ± 2.2 | NS | 22.3 ± 1.9 | 23.1 ± 1.8 | NS |
| High extracellular calcium | ||||||
| Peak tension (mN/mm2) | 47.2 ± 8.6 | 25.2 ± 5.6 | <0.05 | 65.4 ± 12.2 | 49.1 ± 9.0 | <0.05 |
| Time to peak (ms) | 47.6 ± 3.3 | 48.4 ± 2.6 | NS | 64.1 ± 3.6 | 64.5 ± 4.1 | NS |
| Time to 50% relaxation (ms) | 25.8 ± 2.7 | 27.1 ± 3.1 | NS | 45.3 ± 4.8 | 46.5 ± 2.3 | NS |
Values are expressed as means ± SEM. The p-value is estimated by the Student’s t test. The number in parentheses is the number of preparations. Time to peak is the time from stimulus to peak contraction. Time to 50% relaxation is the time from peak to 50% decay of force.