Table 4.
Twitch and Ca2+ transient characteristics of intact myocytes in the absence (Control) or presence of β-adrenergic stimulation by 70 nm isoproterenol
| A.Twith characteristics | ||||
|---|---|---|---|---|
| Group | Condition | Myocyte shortening (%) | t1/2 myocyte shortening (ms) | t1/2 myocyte relengthening (ms) |
| Euthyroid (9) | Control | 3.24 ± 0.37 | 94.5 ± 7.1 | 377.0 ± 54.0 |
| Thyroid deficient (8) | Control | 3.94 ± 0.32 | 201.7 ± 17.0* | 559.4 ± 61.5* |
| Euthyroid (9) | Iso | 19.30 ± 1.07 | 38.0 ± 2.5 | 101.5 ± 7.3 |
| Thyroid deficient (8) | Iso | 18.46 ± 0.63 | 59.4 ± 4.4* | 200.0 ± 8.0* |
| B.Ca2+ | |||||
|---|---|---|---|---|---|
| Group | Condition | Resting F340/F380 | Peak F340/F380 | t fluorescence increase (ms) | t fluorescence decay(ms) |
| Euthyroid (9) | Control | 0.125 ± 0.003 | 0.228 ± 0.007 | 30.0 ± 3.8 | 374.4 ± 27.2 |
| Thyroid deficient (8) | Control | 0.128 ± 0.005 | 0.237 ± 0.013 | 42.0 ± 4.4 | 576.0 ± 67.8* |
| Euthyroid (9) | Iso | 0.137 ± 0.006 | 0.430 ± 0.001 | 33.0 ± 1.6 | 123.0 ± 11.4 |
| Thyroid deficient (8) | Iso | 0.137 ± 0.008 | 0.455 ± 0.028 | 34.7 ± 3.0 | 232.0 ± 14.5* |
All values are expressed as means ±s.e.m., with number of myocytes given in parentheses. Iso, isoproterenol. The ratio of fura-2 fluorescence at 340 and 380 nm was used to measure changes in Ca2+ levels.
*
Significantly different from euthyroid (P < 0.05).