Table 1.
Estimated concentration of SR Ca2+ release per twitch during high-frequency stimulation of toadfish swimbladder fibres (15–16°C)
| Stim no. 1 (μm) | Stim no. 2–4 (μm) | Stim no. 5–10 (μm) | Stim no. 11 20 (μm) | |
|---|---|---|---|---|
| A. Recovery O2 measurements | ||||
| (80 Hz; n = 9) | 735 ± 81 | 339 ± 100 | 252 ± 81 | 152 ± 41 |
| B. Ca2+ modelling (83.3 Hz) | ||||
| 1. Model 1 (see Fig. 6) | 683 | 222 | 180 | — |
| 2. Model 2 (see Fig. 7A) | 732 | 242 | 196 | — |
| 3. Model 3 (see Fig. 7B) | 790 | 339 | 236 | — |
| C. Ca2+ modelling (67–100 Hz) | ||||
| Model 1 (n = 5) | 701 ± 54 | — | — | — |
| Model 2 (n = 5) | 764 ± 65 | — | — | — |
| Model 3 (n = 5) | 819 ± 40 | — | — | — |
All concentrations refer to the myoplasmic water volume in the myofibrillar space (see Methods). In A, the values are means ± SD from the 9 experiments summarized in Fig. 5; to convert to μM units, results in μmoles per kg of muscle were multiplied by 3.13 (see Methods and Supplemental Material). In B, the values are from the single experiment discussed in connection with Figs. 6 and 7; the values for stimuli after the first have been averaged over the indicated number of stimuli. See Results for differences between Models 1–3. In C, the entry gives the mean ± SD for the first-stimulus release in the five experiments discussed in the last section of Results; in three of these fibres, a movement artifact prevented an accurate estimate of release for stimuli after the first. Three t tests did not reveal a statistical difference between the Ca2+ released for the first stimulus estimated by recovery oxygen measurements (A) and that estimated by Models 1, 2 or 3 (C), that is the P values (0.421, 0.507, 0.053, respectively) were greater than the significance level (adjusted to 0.017 by the Bonferroni correction for multiple comparisons).