TABLE I.
Comparison of Parameters Describing Voltage-dependent Activation of Ca2+ Current, Ca2+ Input Flux, and Permeability in γ+/+ (n = 16) and γ−/− (n = 19) Fibers
| Ca2+ current | Input flux peak | Input fluxend level | Permeability peak | Permeabilityend level | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| γ+/+ | γ−/− | γ+/+ | γ−/− | γ+/+ | γ−/− | γ+/+ | γ−/− | γ+/+ | γ−/− | |||
| V 0.5 (mV) | 0.00 ± 1.51 |
0.61 ± 1.06 |
V 0.5 (mV) | −13.16 ± 1.25 |
−13.63 ± 1.02 |
−16.69 ± 1.50 |
−16.92 ± 1.11 |
V 0.5 (mV) | −14.76 ± 1.43 |
−15.11 ± 1.00 |
−13.49 ± 1.65 |
−13.93 ± 1.05 |
| k (mV) | 5.08 ± 0.22 |
5.87 ± 0.30a |
k (mV) | 7.13 ± 0.24 |
6.79 ± 0.21 |
6.05 ± 0.23 |
5.55 ± 0.19 |
k (mV) | 6.82 ± 0.30 |
6.35 ± 0.21 |
5.90 ± 0.35 |
5.48 ± 0.22 |
| g Ca,max (S/F) | 95.02 ± 6.18 |
78.88 ± 7.32 |
a (μM·ms−1) | 121.8 ± 13.43 |
86.99 ± 11.89 |
21.21 ± 1.55 |
16.37 ± 1.84 |
a (%·ms−1) | 3.69 ± 0.31 |
3.59 ± 0.49 |
1.21 ± 0.06 |
1.26 ± 0.11 |
| V Ca (mV) | 67.05 ± 3.41 |
68.43 ± 2.35 |
b (μM·ms−1V−1) | 482.6 ± 153.2 |
497.1 ± 155.1 |
−87.58 ± 9.78 |
−58.23 ± 9.68a |
b (%·ms−1V−1) | 30.85 ± 4.51 |
29.10 ± 4.86 |
0.012 ± 0.77 |
0.052 ± 0.40 |
| Cm (nF) | 5.35 ± 0.24 |
4.22 ± 0.21a |
CaSR,50 (mM) | 2.87 ± 0.24 |
2.34 ± 0.27 |
0.81 ± 0.08 |
0.72 ± 0.12 |
|||||
| i Ca,10 (A/F) | −8.16 ± 0.56 |
−8.67 ± 0.70 |
F 50 (μM·ms−1) | 144.03 ± 17.08 |
108.83 ± 17.81 |
17.00 ± 1.36 |
13.55 ± 1.56 |
P 50 (%·ms−1) | 5.19 ± 0.43 |
4.94 ± 0.68 |
1.22 ± 0.06 |
1.26 ± 0.10 |
Voltage dependence was described by the product of a Boltzmann function (see Eq. 2) with voltage of half-maximal activation V 0.5 and voltage sensitivity k and a linear function. For flux and permeability, a and b describe the linear part (i.e., F = a + bV) of the activation curve at large voltages. a is the extrapolated value of this part at V = 0 mV. In the case of the Ca2+ current, the linear function corresponds to the open channel current–voltage relation. g Ca,max is the maximal Ca2+ conductance (normalized by linear capacitance Cm) and V Ca is the apparent reversal potential (see Eq. 1). i Ca,10 is the maximal inward current density (at +10 mV), F 50 the Ca2+ input flux at +50 mV, and P 50 the permeability at +50 mV. CaSR,50 is the estimated Ca2+ content of the SR determined in the depletion analysis for the permeability calculation using depolarizing pulses to +50 mV. It was split up into the initial value (listed under column “permeability peak”) and the value at the end of the 100-ms pulse (listed under column “permeability end level”). Errors are SEM.
P values were 0.047, 0.042, and 0.0013 for the three parameters k, b, and Cm that showed significant differences.