Interstitial Po2 determination by phosphorescence quenching microscopy

Objective: This study introduces the technique of microinjection of phosphor probe into skeletal muscle tissue to determine oxygen tension (Po(2)) in the interstitium by phosphorescence quenching microscopy. Method: The spinotrapezius muscle of Wistar-Kyoto rats weighing 240-280 g was surgically isolated and underwent the microinjection procedure. We measured the spatial distribution of phosphor probe 10, 30, and 80 minutes after injection; the tissue Po(2) at sites adjacent to arteriolar and venular microvessels,and the decline in tissue Po(2) during a 3-minute period of 8-Hz contraction. Results: The phosphorescence signal from the probe was undetectable outside a 2.5-min radius from the site of injection at the 10-minute time point, increased to measurable values after 30 minutes, and was double the 30-minute intensity value after 80 minutes. When used to measure periarteriolar Po(2), the tissue microinjection technique demonstrated a nonlinear fall in tissue Po(2) with distance away from secondary arterioles (30-40 mum diameter). Conversely, perivenular tissue Po(2) increased in a nonlinear manner with distance away from secondary venules (60-70 mum diameter). The tissue Po(2) at distances of 16 mum and greater from both types of secondary microvessels was significantly different from values taken directly over the centerline of these microvessels. During muscle contraction, the Po(2) fell from a mean precontraction value of 28.3 +/- 4.9 mmHg to 8.2 +/- 0.9 mmHg at the end of the contraction period. Conclusions: These observations indicate that the microinjection technique yields values for tissue Po(2) that are in good agreement with previously published results using oxygen microclectrodes.