Table 2.
MHC I and IIa single muscle fibre activation threshold (pCa10), Ca2+ sensitivity (pCa50), force–Ca2+ slope (Hill coefficient, n), Sr2+ sensitivity (pSr50) and differential sensitivity ( = pCa50– pSr50, Δ) in young and old men prior to and after 2 weeks of immobilisation
| Young men | Old men | |||
|---|---|---|---|---|
| MHC I | Pre (n = 40) | Post (n = 35) | Pre (n = 44) | Post (n = 34) |
| pCa10 | 6.23 ± 0.04 | 6.30 ± 0.07 | 6.31 ± 0.05 | 6.22 ± 0.04a |
| pCa50 | 5.90 ± 0.03 | 5.92 ± 0.04 | 5.96 ± 0.04 | 5.93 ± 0.03a |
| n | 3.35 ± 0.20 | 3.15 ± 0.26 | 3.17 ± 0.16 | 3.58 ± 0.19a |
| Pre (n = 33) | Post (n = 33) | Pre (n = 41) | Post (n = 32) | |
| pSr50 | 6.27 ± 0.03 | 6.27 ± 0.03 | 6.34 ± 0.01 | 6.32 ± 0.02a,e |
| Δ50 | −0.37 ± 0.02 | −0.36 ± 0.02 | −0.38 ± 0.03 | −0.38 ± 0.01a |
| MHC IIa | Pre (n = 40) | Post (n = 28) | Pre (n = 15) | Post (n = 16) |
| pCa10 | 6.08 ± 0.03b | 6.01 ± 0.04a,b | 6.00 ± 0.06b | 5.92 ± 0.06b |
| pCa50 | 5.86 ± 0.02b | 5.79 ± 0.02a,b | 5.78 ± 0.05b | 5.73 ± 0.05b |
| n | 4.80 ± 0.25b | 5.77 ± 0.63a,b | 4.67 ± 0.47b | 7.36 ± 1.26b |
| Pre (n = 36) | Post (n = 21) | Pre (n = 13) | Post (n = 12) | |
| pSr50 | 5.72 ± 0.02b | 5.69 ± 0.03a,b | 5.67 ± 0.04b | 5.53 ± 0.10b,e |
| Δ50 | 0.14 ± 0.02b | 0.12 ± 0.02b | 0.14 ± 0.03b | 0.26 ± 0.07b,d |
Number of fibres is given in parentheses.
a
Different from prior to immobilisation
b
different from MHC I
c
immobilisation-induced change different from that observed in MHC I
d
different from young
e
immobilisation-induced change different from that observed in young.
The listed values are based on the mean values obtained for each given fibre.