Determination of PO2 and its heterogeneity in single capillaries
Zheng, L.; Golub, A.S.; Pittman, R.N.
American Journal of Physiology 271(1 Pt 2): H365-H372
1996
ISSN/ISBN: 0002-9513 PMID: 8760194 Document Number: 457644
We have applied the phosphorescence lifetime technique (Vanderkooi, J. M., G. Maniara, T. J. Green, and D. F. Wilson. J. Biol. Chem. 262: 5476-5482, 1987) to determine oxygen tension in single capillaries of the hamster retractor muscle. Palladium meso-tetra(4-carboxyphenyl)porphine (10 mg/ml, pH 7.40, bound to bovine serum albumin) was used as the phosphorescent oxygen sensor. Our measurement system consisted of a microscope configured for epi-illumination, a strobe flash lamp, a 430-nm bandpass excitation filter, and a 630-nm cut-on emission filter. A rectangular diaphragm was used to limit the illumination field to 10 mu-m times 10 mu-m, and an end-window photomultiplier tube was used to detect the phosphorescence signal, which was then input to an analog-to-digital board in a personal computer. In vitro calibrations were carried out at 37 degree C on samples flowing through a glass capillary tube (diameter, 300 mu-m) at four different O-2 concentrations (0, 2.5, 5, and 7.5%). In vivo tests were carried out on arterioles, capillaries, and venules of the retractor muscle of anesthetized hamsters. The phosphorescent compound was administered by injection into a jugular vein (20 mg/kg). Phosphorescence decay curves were analyzed by a new model of heterogeneous oxygen distribution in the excitation/emission volume. Mean P-O-2 values and the local P-O-2 gradients within the excitation/ emission volume were calculated from phosphorescence lifetimes obtained from individual decay curves. The time course of P-O-2 obtained during 0.5-s measurement periods (5 decay curves at 0.1-s intervals) at a given site along a capillary indicated the presence of a gradient in P-O-2 within the plasma space between and near red blood cells. Similar P-O-2 gradients were also detected in arterioles and venules. Mean P-O-2 values for arterioles, capillaries, and venules over the 0.5-s observation period were 27 +- 5, 14 +- 2, and 11 +- 3 (SD) mmHg, respectively. The magnitude of the P-O-2 gradient in the arterioles, capillaries, and venules was 6 +- 1, 4 +- 1, and 2 +- 1 mmHg/mu-m, respectively.