Skeletal muscle microvascular and interstitial PO2 from rest to contractions.

KEY POINTS: Oxygen pressure gradients across the microvascular walls are essential for oxygen diffusion from blood to tissue cells. At any given flux, the magnitude of these transmural gradients is proportional to the local resistance. The greatest resistance to oxygen transport into skeletal muscle is considered to reside in the short distance between red blood cells and myocytes. Although crucial to oxygen transport, little is known about transmural pressure gradients within skeletal muscle during contractions. We evaluated oxygen pressures within both the skeletal muscle microvascular and interstitial spaces to determine transmural gradients during the rest-contraction transient in anaesthetized rats. The significant transmural gradient observed at rest was sustained during submaximal muscle contractions. Our findings support that the blood-myocyte interface provides substantial resistance to oxygen diffusion at rest and during contractions and suggest that modulations in microvascular haemodynamics and red blood cell distribution constitute primary mechanisms driving increased transmural oxygen flux with contractions. ABSTRACT: Oxygen pressure (PO2) gradients across the blood-myocyte interface are required for diffusive O2 transport, thereby supporting oxidative metabolism. The greatest resistance to O2 flux into skeletal muscle is considered to reside between the erythrocyte surface and adjacent sarcolemma, although this has not been measured during contractions. We tested the hypothesis that O2 gradients between skeletal muscle microvascular (PO2 mv ) and interstitial (PO2 is ) spaces would be present at rest and maintained or increased during contractions. PO2 mv and PO2 is   were determined via phosphorescence quenching (Oxyphor probes G2 and G4, respectively) in the exposed rat spinotrapezius during the rest-contraction transient (1 Hz, 6 V; n = 8). PO2 mv was higher than PO2 is in all instances from rest (34.9 ± 6.0 versus 15.7 ± 6.4) to contractions (28.4 ± 5.3 versus 10.6 ± 5.2 mmHg, respectively) such that the mean PO2 gradient throughout the transient was 16.9 ± 6.6 mmHg (P < 0.05 for all). No differences in the amplitude of PO2 fall with contractions were observed between the microvasculature and interstitium (10.9 ± 2.3 versus 9.0 ± 3.5 mmHg, respectively; P > 0.05). However, the speed of the PO2 is fall during contractions was slower than that of PO2 mv (time constant: 12.8 ± 4.7 versus 9.0 ± 5.1 s, respectively; P < 0.05). Consistent with our hypothesis, a significant transmural gradient was sustained (but not increased) from rest to contractions. This supports that the blood-myocyte interface is the site of a substantial PO2 gradient driving O2 diffusion during metabolic transients. Based on Fick's law, elevated O2 flux with contractions must thus rely primarily on modulations in effective diffusing capacity (mainly erythrocyte haemodynamics and distribution) as the PO2 gradient is not increased.

Novel instrumentation to determine peel force in vivo and preliminary studies with adhesive skin barriers.

BACKGROUND/PURPOSE: Adhesive barriers secure medical devices to skin. Laboratory adhesion models are not predictive of in vivo performance. The objectives of these studies were to validate a novel peel force device, and to investigate relationships between barrier formulations, barrier width, subjective discomfort during barrier removal, and substrates. METHODS: Three hydrocolloid barrier formulations in three widths were adhered to ethylene/methyl acrylate film (EMA), VITRO-SKIN(®) and human abdominal skin. Peel force was measured using a MTS Insight™ and a cyberDERM Inc. Mini Peel Tester (CMPT). Subjects reported their discomfort. RESULTS: Peel forces were highly correlated between devices and highly dependent on substrate. Data suggested a weak direct association between peel force in vivo and discomfort. The 0.5″-wide barriers had the most precise peel forces measurements in vivo. A weak negative relationship between normalized peel force and barrier width on human skin was found. There was a strong positive relationship between peel force in vivo and on EMA, whereas no correlation was observed with VITRO-SKIN(®). CONCLUSION: The CMPT correlates with a standard instrument and can advantageously investigate adhesion in vivo. Barrier width and substrate impact the reliability and predictability of peel force measurements.

Genetic approaches to dissect plant nonhost resistance mechanisms.

Nonhost resistance (NHR) refers to the immunity of most tested genotypes of a plant species to most tested variants of a pathogen species. Thus, NHR is broad spectrum and durable in nature and constitutes a major safety barrier against invasion of a myriad of potentially pathogenic microbes in any plants including domesticated crops. Genetic study of NHR is generally more difficult compared to host resistance mainly because NHR is genetically more complicated and often lacks intraspecific polymorphisms. Nevertheless, substantial progress has been made towards the understanding of the molecular basis of NHR in the past two decades using various approaches. Not surprisingly, molecular mechanisms of NHR revealed so far encompasses pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity. In this review, we briefly discuss the inherent difficulty in genetic studies of NHR and summarize the main approaches that have been taken to identify genes contributing to NHR. We also discuss new enabling strategies for dissecting multilayered NHR in model plants with a focus on NHR against filamentous pathogens, especially biotrophic pathogens such as powdery mildew and rust fungi.

Salivary biomarkers of periodontal disease in response to treatment.

BACKGROUND: Salivary biomarkers of periodontitis were assessed longitudinally to determine response to therapy. METHODS: A 6-month case-controlled study of adults with chronic periodontitis was performed, with 33 participants receiving oral hygiene instructions (OHI) alone and 35 with scaling and root planing (SRP) combined with OHI. Saliva samples collected at week 0, 16 and 28 were analysed for interleukin (IL)-1ß, IL-8, macrophage inflammatory protein (MIP)-1α, matrix metalloproteinase-8 (MMP-8), osteoprotegerin (OPG), and tumour necrosis factor-α (TNF)-α. Clinical measures of periodontal disease were recorded at each visit. RESULTS: All parameters of periodontal health improved significantly in both groups by week 16 (p<0.0001) with the SRP group demonstrating greater benefit at week 16 and 28. Baseline OPG and TNF-α levels changed significantly at both follow-up visits (p<0.03), regardless of treatment group. IL-1ß and MMP-8 levels decreased significantly from baseline (p<0.04) in the SRP group only. OPG, MMP-8, and MIP-1α were significantly reduced in responders compared with non-responders (p=0.04, 0.01, 0.05, respectively). In receiver-operating characteristic analyses, MMP-8 produced the highest area under the curve (0.7; p=0.01). CONCLUSION: Salivary levels of IL-1ß, MMP-8, OPG, and MIP-1α reflected disease severity and response to therapy suggesting their potential utility for monitoring periodontal disease status.

An Easy and Flexible Inoculation Method for Accurately Assessing Powdery Mildew-Infection Phenotypes of Arabidopsis and Other Plants.

Reducing crop losses due to fungal diseases requires improved understanding of the mechanisms governing plant immunity and fungal pathogenesis, which in turn requires accurate determination of disease phenotypes of plants upon infection with a particular fungal pathogen. However, accurate disease phenotyping with unculturable biotrophic fungal pathogens such as powdery mildew is not easy to achieve and can be a rate-limiting step of a research project. Here, we have developed a safe, efficient, and easy-to-operate disease phenotyping system using the Arabidopsis-powdery mildew interaction as an example. This system mainly consists of three components: (i) a wooden inoculation box fitted with a removable lid mounted with a stainless steel or nylon mesh of ~50 µm pores for inoculating a flat of plants with fungal spores, (ii) a transparent plastic chamber with a small front opening for minimizing spore escape while conducting inoculation inside, and (iii) a spore-dislodging and distribution method for even and effective inoculation. The protocols described here include the steps and parameters for making the inoculation box and the plastic chamber at a low cost, and a video demonstration of how to use the system to enable even inoculation with powdery mildew spores, thereby improving accuracy and reproducibility of disease phenotyping.

Validity and reliability of a pad test model using a simulated urine leak and healthy continent females.

The objective of this study was to determine the validity and reliability of a modified pad test to assess urinary incontinence. Urine leakage was simulated using normal saline that was dosed onto super-absorbent incontinence pads, and worn by healthy continent females over two sequential 12-hour time periods. The results indicate that the two x 12-hour pad test provides a reliable assessment of urine leak in female subjects.

Salivary immunoglobulin A response to a collegiate rugby game.

Transient fluctuations in immune function after heavy exercise have been linked to an increased incidence of infection in athletes. Several parameters of immunity, including salivary immunoglobulin A (IgA), are affected by heavy exercise in the laboratory setting. However, few observations have been made during true competition. We tested the hypothesis that salivary IgA levels will be decreased after a collegiate rugby game. Saliva samples obtained from 16 men's college rugby players before and after an 80-minute regulation rugby game were analyzed for total volume, IgA, total protein content, and osmolality. Salivary IgA was expressed relative to secretion rate (s-IgA), osmolality (IgA-Osm), and total protein (IgA-Pro). No significant pregame-postgame changes in salivary IgA were observed (s-IgA: -13%, IgA-Osm: -16%, IgA-Pro: +10%). These data indicate that strenuous physical activity, such as a competitive rugby game, does not affect IgA levels. More study on the immune response to athletic competition is needed.

Dynamics of microvascular oxygen pressure during rest-contraction transition in skeletal muscle of diabetic rats.

Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (QO(2)). In control (C; n = 6) and streptozotocin-induced diabetic (D: n = 6, plasma glucose = 25.3 +/- 3.9 mmol/l and C: 8.3 +/- 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular PO(2) [Pm(O(2)), which reflects the dynamic balance between O(2) utilization (VO(2)) and QO(2)] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. Pm(O(2)) data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, Pm(O(2)) at rest was lower (C: 31.2 +/- 3.2 mmHg; D: 24.3 +/- 1.3 mmHg, P < 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 +/- 1.8 s; D: 7.6 +/- 2.1 s, P < 0.05) and with a reduced mean response time (C: 31.4 +/- 3.3 s; D: 23.9 +/- 3.1 s, P < 0.05). Pm(O(2)) exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 +/- 1.1 mmHg, P < 0.05), which was absent in C muscles. These results indicate an altered VO(2)-to-QO(2) matching across the rest-exercise transition in muscles of D rats.

Effects of prior contractions on muscle microvascular oxygen pressure at onset of subsequent contractions.

In humans, pulmonary oxygen uptake (.V(O2)) kinetics may be speeded by prior exercise in the heavy domain. This "speeding" arises potentially as the result of an increased muscle O(2) delivery (.Q(O2)) and/or a more rapid elevation of oxidative phosphorylation. We adapted phosphorescence quenching techniques to determine the.Q(O2)-to-O(2) utilization (.Q(O2)/.V(O2)) characteristics via microvascular O(2) pressure (P(O2,m)) measurements across sequential bouts of contractions in rat spinotrapezius muscle. Spinotrapezius muscles from female Sprague-Dawley rats (n = 6) were electrically stimulated (1 Hz twitch, 3-5 V) for two 3 min bouts (ST(1) and ST(2)) separated by 10 min rest. P(O2,m) responses were analysed using an exponential + time delay (TD) model. There was no significant difference in baseline and DeltaP(O2,m) between ST(1) and ST(2) (28.5 +/- 2.6 vs. 27.9 +/- 2.4 mmHg, and 13.9 +/- 1.8 vs. 14.1 +/- 1.3 mmHg, respectively). The TD was reduced significantly in the second contraction bout (ST(1), 12.2 +/- 1.9; ST(2), 5.7 +/- 2.2 s, P < 0.05), whereas the time constant of the exponential P(O2,m) decrease was unchanged (ST(1), 16.3 +/- 2.6; ST(2), 17.6 +/- 2.7 s, P > 0.1). The shortened TD found in ST(2) led to a reduced time to reach 63 % of the final response of ST(2) compared to ST(1) (ST(1), 28.3 +/- 3.0; ST(2), 20.2 +/- 1.8 s, P < 0.05). The speeding of the overall response in the absence of an elevated P(O2,m) baseline (which had it occurred would indicate an elevated.Q(O2)/.V(O2) or muscle blood flow suggests that some intracellular process(es) (e.g. more rapid increase in oxidative phosphorylation) may be responsible for the increased speed of P(O2,m) kinetics after prior contractions under these conditions.