Publications

Rest-to-work and work-to-rest transients of interstitial PO2 in spinotrapezius muscle of young and old male rats

Abstract

Muscle function declines with age. Since the primary energy source for contraction is aerobic, this study investigated age-related changes in muscle oxygenation dynamics to: characterize PO2 transients during rest-work transitions, identify age-specific differences in oxygen delivery/utilization balance, and examine the relationship between interstitial and arterial oxygen tension (PO2). Interstitial PO2 was measured with a high-resolution stroboscopic phosphorescence quenching technique to map intra-contractile dynamics during changes in muscle activity-rest-to-work (RtW) and work-to-rest (WtR) in rats aged three (young) and 23 (old) months. RtW (τw) and WtR (τr) PO2 transitions had lag periods and mono-exponential time constants. In young muscles, lag was 4 s, τw = 9.0 ± 3.7 s, and τr = 15.4 ± 3.9 s. For old, lag was also 4 s with increases to τw = 15.9 ± 3.5 s and τr = 41.4 ± 8.3 s. Resting PO2's were higher for young than for old (66.7 ± 13.7 vs. 60.2 ± 13.0 mmHg; p < 0.05). Work reduced PO2 with a greater effect on old (42.5 ± 14.0 vs. 28.3 ± 16.5 mmHg; p 200 ms), which was absent in old. Further, sustained exercise in young showed a rising trend in PO2, while old remained at nadir. The missing PO2 spike in aged muscle contributes to reduced PO2 during work and may explain age-related loss of endurance.