AUTHOR=Golub Aleksander S. , Song Bjorn K. , Nugent William H. , Pittman Roland N. 

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

JOURNAL=Frontiers in Physiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2023.1172834

DOI=10.3389/fphys.2023.1172834

ISSN=1664-042X

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