Biomedical subjects

Aleksander S Golub

Publications and source records attributed to Aleksander S Golub.

6 recordsLinked to original sources

PubMed2005

Erythrocyte-associated transients in PO2 revealed in capillaries of rat mesentery.

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-micros pulses of light, concentrated by a x100 objective, onto a spot 0.9 microm in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.

Animals↗

PubMed2005

Rate of decrease of PO2 from an arteriole with arrested flow.

When flow to a region is arrested, the amount of oxygen contained within the stationary blood decreases at a rate dependent on the oxygen utilization of the surrounding tissue. We used phosphorescence quenching microscopy to measure arteriolar PO2 in the mesentery of male Sprague-Dawley rats. Flow was quickly stopped (< 1 s) by occluding the microvessels using an inflatable Saran bag attached to the microscope objective. The rate of decline in PO2 following occlusion yielded a calculated initial flux of oxygen out of the vessel lumen of 8.0 x 10(-7) ml O2 cm(-2) sec(-1). An upper limit on the oxygen consumption of the arteriolar wall was calculated by assuming that all of the oxygen in the lumen was consumed by the wall at the initial rate. This value was 2.5 x 10(-3) ml O2 cm(-3) sec(-1) and is an overestimate since the oxygen consumption of the nearby parenchymal cells was neglected. The calculated maximum oxygen consumption of the wall is more than an order of magnitude smaller than that reported previously for arterioles in the rat mesentery (6.5 x 10(-2) ml O2 cm(-3) sec(-1)). We conclude that oxygen consumption of the arteriolar wall is similar to previous values for other vascular tissues.

Animals↗

PubMed2005

Effect of oxygen consumption by measuring method on PO2 transients associated with the passage of erythrocytes in capillaries of rat mesentery.

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-mus pulses of light, concentrated by a x100 objective, onto a spot 0.9 mum in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.

Animals↗

PubMed2003

Thermostatic animal platform for intravital microscopy of thin tissues.

We describe a novel temperature-controlled, all-on-board design platform for intravital microscopy of thin tissues in small laboratory animals. The apparatus uses transparent heaters and miniature controllers to control independently the temperature of the tissue pedestal and animal heating pad, as well as the animal core temperature. The system ensures a uniform temperature for a thin tissue placed on the surface of a transparent window and maintenance of the animal's core temperature without overheating. This platform provides an alternative to warm superfusion solution for in vivo microscopy, under circumstances where a well-controlled temperature is required. All components of the apparatus are commercially available, inexpensive and reliable, thereby simplifying its assembly. The platform is convenient for use with trans- and epi-illumination and does not interfere with movement of the microscope stage.

Animals↗

PubMed2002

Recovery of radial PO(2) profiles from phosphorescence quenching measurements in microvessels.

Work by previous investigators has indicated that a substantial amount of oxygen diffuses from the precapillary circulation. These losses imply that there should be radial gradients of oxygen tension (PO(2)) in arterioles, leading to a non-uniform distribution of oxygen within these microvessels. We have employed the phosphorescence quenching method to measure oxygen, allowing us to evaluate the heterogeneity of PO(2) inside short segments of microvessels. The phosphorescence decay curve contains information about the distribution of oxygen within the excited volume and the distribution can be represented as a histogram, by decomposing the decay curve into several components with weights proportional to the volume fraction of plasma with different PO(2), under the condition of a high signal-to-noise ratio. Furthermore, the histogram can be converted into a radial profile of PO(2), based on the assumptions of a circular vascular lumen, axisymmetric distribution of oxygen and monotonic PO(2) profile. Albumin-bound Pd-porphyrin phosphor was infused into the circulation of hamsters and excited by flash illumination at 10 Hz, with a square region of excitation light just covering the entire lumen, (i.e. width of region equaled luminal diameter) of microvessels in the hamster mesentery. A set of 50 curves (5 s of data) was averaged to obtain a decay curve with low noise. Curves were analyzed with the above histogram procedure, and this analysis allowed us to distinguish between PO(2) values originating from intra and extravascular subvolumes. The intravascular PO(2) in these microvessels was very heterogeneous, which could be explained by the existence of significant radial PO(2) gradients. The radial PO(2) gradients were estimated to be approximately 1 mmHg/microm.

Animals↗

PubMed2002

Interstitial PO(2) 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-mm 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 microm diameter). Conversely, perivenular tissue PO(2) increased in a nonlinear manner with distance away from secondary venules (60-70 microm diameter). The tissue PO(2) at distances of 16 microm 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 microelectrodes.

Animals↗