Dynamics of PO2 and VO2 in resting and contracting rat spinotrapezius muscle

• Published in: Frontiers in physiology 2023-07, Vol.14, p.1172834-1172834
• Main Authors: Golub, Aleksander S., Song, Bjorn K., Nugent, William H., Pittman, Roland N.
• Format: Article
• Language: English
• Subjects: microcirculation; muscle contraction; oxygen consumption; oxygen supply; oxygen supply-demand matching; Physiology
• ISSN: 1664-042X; 1664-042X
• DOI: 10.3389/fphys.2023.1172834

This study examined changes in interstitial PO 2 , which allowed calculation of VO 2 during periods of rest, muscle contraction and recovery using an in situ rat spinotrapezius muscle preparation. The PO 2 was measured using phosphorescence quenching microscopy and the muscle VO 2 was calculated as the rate of O 2 disappearance during brief periods of muscle compression to stop blood flow with a supra-systolic pressure. The PO 2 and VO 2 measurements were made during “5 s compression and 15 s recovery” (CR) cycles. With all three stimulation frequencies, 1, 2 and 4 Hz, the fall in interstitial PO 2 and rise in VO 2 from resting values occurred within the first 20 s of contraction. The PO 2 during contraction became lower as stimulation frequency increased from 1 to 4 Hz. VO 2 was higher at 2 Hz than at 1 Hz contraction. With cessation of stimulation, PO 2 began increasing exponentially towards baseline values. After 1 and 2 Hz contraction, the fall in muscle VO 2 was delayed by one CR cycle and then exponentially decreased towards resting values. After 4 Hz stimulation, VO 2 increased for 2 cycles and then decreased. The post-contraction transients of PO 2 and VO 2 were not synchronous and had different time constants. With further analysis two distinct functional responses were identified across all stimulation frequencies having PO 2 during contraction above or below 30 mmHg. The corresponding VO 2 responses were different - for “high” PO 2 , muscle VO 2 reached high levels, while for the “low” PO 2 data set muscle VO 2 remained low. Recovery patterns were similar to those described above. In summary, local microscopic PO 2 and VO 2 were measured in resting and contracting muscle in situ and the post-contraction transients of PO 2 and VO 2 were all much slower than the onset transients.