Skeletal muscle contraction-induced vasodilation in the microcirculation

The role of pannexin/purinergic signaling in intervascular communication from capillaries during skeletal muscle contraction in male Golden hamsters

We sought to determine the physiological relevance of pannexin/purinergic-dependent signaling in mediating conducted vasodilation elicited by capillary stimulation through skeletal muscle contraction. Using hamster cremaster muscle and intravital microscopy we stimulated capillaries through local muscle contraction while observing the associated upstream arteriole. Capillaries were stimulated with muscle contraction at low and high contraction (6 and 60CPM) and stimulus frequencies (4 and 40 Hz) in the absence and presence of pannexin blocker mefloquine (MEF; 10-5 M), purinergic receptor antagonist suramin (SUR 10-5 M) and gap-junction uncoupler halothane (HALO, 0.07%) applied between the capillary stimulation site and the upstream arteriolar observation site. Conducted vasodilations elicited at 6CPM were inhibited by HALO while vasodilations at 60CPM were inhibited by MEF and SUR. The conducted response elicited at 4 Hz was inhibited by MEF while the vasodilation at 40 Hz was unaffected by any blocker. Therefore, upstream vasodilations resulting from capillary stimulation via muscle contraction are dependent upon a pannexin/purinergic-dependent pathway that appears to be stimulation parameter-dependent. Our data highlight a physiological importance of the pannexin/purinergic pathway in facilitating communication between capillaries and upstream arteriolar microvasculature and, consequently, indicating that this pathway may play a crucial role in regulating blood flow in response to skeletal muscle contraction.

Uphill versus downhill high-intensity training effectiveness in preserving vascular function and exercise performance in runners who reduce their regular endurance training

Purpose

The COVID-19 restrictions have limited outdoor physical activities. High-intensity training (HIT) may be a valid indoor alternative. We tested whether an indoor HIT is effective in maintaining vascular function and exercise performance in runners who reduce their usual endurance training, and whether a downhill HIT is as effective as an uphill one for such purposes.

Methods

Sixteen runners performed the same 6-week HIT either uphill (UP, eight runners) or downhill (DOWN, eight runners). Eight runners continuing their usual endurance training acted as a control group (CON). The following data were collected before vs after our HIT: vascular conductance during rapid leg vasodilation to assess vasodilation capacity; V̇O_2max through running incremental test to exhaustion; 2000 m running time; neuromuscular indexes related to lower-limb muscle strength.

Results

Both uphill and downhill HIT failed in maintaining the pre-HIT leg vasodilation capacity compared to CON, which was, however, blunted more after uphill than downhill HIT. V̇O_2max and 2000 m time were similar after downhill HIT compared to CON, and augmented after uphill HIT compared to CON and DOWN. Indexes of lower-limb muscle strength were similar before vs after HIT and among groups.

Conclusion

Our HIT was ineffective in maintaining the pre-HIT leg vasodilation capacity compared to runners continuing their usual low-intensity endurance training, but did not lead to reductions in V̇O_2max, 2000 m time performance, and indexes related to lower-limb muscle strength. Our data show an appealing potential for preserving exercise performance with low cardiorespiratory effort via downhill running.

Capillary communication: the role of capillaries in sensing the tissue environment, coordinating the microvascular, and controlling blood flow

Historically, capillaries have been viewed as the microvascular site for flux of nutrients to cells and removal of waste products. Capillaries are the most numerous blood vessel segment within the tissue, whose vascular wall consists of only a single layer of endothelial cells and are situated within microns of each cell of the tissue, all of which optimizes capillaries for the exchange of nutrients between the blood compartment and the interstitial space of tissues. There is, however, a growing body of evidence to support that capillaries play an important role in sensing the tissue environment, coordinating microvascular network responses, and controlling blood flow. Much of our growing understanding of capillaries stems from work in skeletal muscle and more recent work in the brain, where capillaries can be stimulated by products released from cells of the tissue during increased activity and are able to communicate with upstream and downstream vascular segments, enabling capillaries to sense the activity levels of the tissue and send signals to the microvascular network to coordinate the blood flow response. This review will focus on the emerging role that capillaries play in communication between cells of the tissue and the vascular network required to direct blood flow to active cells in skeletal muscle and the brain. We will also highlight the emerging central role that disruptions in capillary communication may play in blood flow dysregulation, pathophysiology, and disease.

Chuanzhitongluo capsule ameliorates microcirculatory dysfunction in rats: Efficacy evaluation and metabolic profiles

Background: Ischemic stroke is a leading cause of mortality and disability worldwide. Microcirculatory dysfunction is the foremost hindrance for a good clinical prognosis in ischemic stroke patients. Clinical researches show that Chuanzhitongluo capsule (CZTL) has a curative effect during the recovery period of ischemic stroke, which contributes to a good prognosis. However, it is not known whether CZTL treats ischemic stroke by ameliorating microcirculation dysfunction.

Objective: In this study, we investigated the influence of CZTL on microcirculation and its underlying mechanism.

Methods: A rat model of acute microcirculatory dysfunction was established by stimuli of adrenaline and ice water. The microcirculatory damage in model rats and the efficacy of CZTL were assessed by detecting laser speckle contrast imaging, coagulation function, hemorheology, vasomotor factor and microcirculation function. The potential mechanism of CZTL action was explored by the untargeted metabolomic analysis based on ultra-performance liquid chromatography-quadrupole-time of flight-mass spectrometry.

Results: Laser speckle contrast imaging showed that model rats suffered low perfusion in ears, feet and tails, and CZTL treatment increased microcirculatory blood flow. Coagulation function detection results showed that CZTL diminished the reduction of thrombin time, prothrombin time, activated partial thromboplastin time and the elevated fibrinogen level caused by acute microcirculatory dysfunction. Furthermore, CZTL could recover the increased blood viscosity as well as the abnormal vasomotor and microcirculation function in rats with acute microcirculatory dysfunction. Metabolomics analysis indicated that CZTL might regulate sphingolipid metabolism and arachidonic acid metabolism to exert protective effects on microcirculation.

Conclusion: These results elucidated that CZTL was highly effective against microcirculatory dysfunction and its potential mechanisms related with the modulation of sphingolipid and arachidonic acid metabolic pathways. The present study provided a new perspective on the clinical application of CZTL, and it contribute to explore novel therapeutic drug against microcirculatory dysfunction.

Capillaries communicate with the arteriolar microvascular network by a pannexin/purinergic-dependent pathway in hamster skeletal muscle

We sought to determine if a pannexin/purinergic-dependent intravascular communication pathway exists in skeletal muscle microvasculature that facilitates capillary communication with upstream arterioles that control their perfusion. Using the hamster cremaster muscle and intravital microscopy, we locally stimulated capillaries and observed the vasodilatory response in the associated upstream 4A arteriole. We stimulated capillaries with vasodilators relevant to muscle contraction: 10^-6 M S-nitroso-N-acetyl-dl-penicillamine (SNAP; nitric oxide donor), 10^-6 M adenosine, 10 mM potassium chloride, 10^-5 M pinacidil, as well as a known initiator of gap-junction-dependent intravascular communication, acetylcholine (10^-5 M), in the absence and the presence of the purinergic membrane receptor blocker suramin (10^-5 M), pannexin blocker mefloquine (2 × 10^-5 M), or probenecid (5 × 10^-6 M) and gap-junction inhibitor halothane (0.07%) applied in the transmission pathway, between the capillary stimulation site and the upstream 4A observation site. Potassium chloride, SNAP, and adenosine-induced upstream vasodilations were significantly inhibited by suramin, mefloquine, and probenecid but not halothane, indicating the involvement of a pannexin/purinergic-dependent signaling pathway. Conversely, SNAP-induced upstream vasodilation was only inhibited by halothane indicating that communication was facilitated by gap junctions. Both pinacidil and acetylcholine were inhibited by suramin but only acetylcholine was inhibited by halothane. These data demonstrate the presence of a pannexin/purinergic-dependent communication pathway between capillaries and upstream arterioles controlling their perfusion. This pathway adds to the gap-junction-dependent pathway that exists at this vascular level as well. Given that vasodilators relevant to muscle contraction can use both of these pathways, our data implicate the involvement of both pathways in the coordination of skeletal muscle blood flow.NEW & NOTEWORTHY Blood flow control during increased metabolic demand in skeletal muscle is not fully understood. Capillaries have been implicated in controlling blood flow to active skeletal muscle, but how capillaries communicate to the arteriolar vascular network is not clear. Our study uncovers a novel pathway through which capillaries can communicate to upstream arterioles to cause vasodilation and therefore control perfusion. This work implicates a new vascular communication pathway in blood flow control in skeletal muscle.

Do skeletal muscle motor units and microvascular units align to help match blood flow to metabolic demand?

PURPOSE

We explore the motor unit recruitment and control of perfusion of microvascular units in skeletal muscle to determine whether they coordinate to match blood flow to metabolic demand.

METHODS

The PubMed database was searched for historical, current and relevant literature.

RESULTS

A microvascular, or capillary unit consists of 2-20 individual capillaries. Individual capillaries within a capillary unit cannot increase perfusion independently of other capillaries within the unit. Capillary units perfuse a short segment of approx. 12 muscle fibres located beside each other. Motor units consist of muscle fibres that can be dispersed widely within the muscle volume. During a contraction, where not all motor units are recruited, muscle fibre contraction will result in increased perfusion of associated capillaries as well as all capillaries within that capillary unit. Perfusion of the entire capillary unit will result in an increased blood flow delivery to muscle fibres associated with active motor unit plus approximately 11 other inactive muscle fibres within the same region. This will result in an overperfusion of the muscle resulting in blood flow in excess of the muscle fibre needs.

CONCLUSIONS

Given the architecture of the capillary units and the dispersed nature of muscle fibres within a motor unit, during submaximal contractions, where not all motor units are recruited, there will be a greater perfusion to the muscle than that predicted by the number of active muscle fibres. Such overperfusion brings into question if blood flow and metabolic demand are as tightly matched as previously assumed.

Calcium Signaling in Schwann cells

In addition to providing structural, metabolic and trophic support to neurons, glial cells of the central, peripheral and enteric nervous systems (CNS, PNS, ENS) respond to and regulate neural activity. One of the most well characterized features of this response is an increase of intracellular calcium. Astrocytes at synapses of the CNS, oligodendrocytes along axons of the CNS, enteric glia associated with the cell bodies and axonal varicosities of the ENS, and Schwann cells at the neuromuscular junction (NMJ) and along peripheral nerves of the PNS, all exhibit this response. Recent technical advances have facilitated the imaging of neural activity-dependent calcium responses in large populations of glial cells and thus provided a new tool to evaluate the physiological significance of these responses. This mini-review summarizes the mechanisms and functional role of activity-induced calcium signaling within Schwann cells, including terminal/perisynaptic Schwann cells (TPSCs) at the NMJ and axonal Schwann cells (ASCs) within peripheral nerves.

HIF-hypoxia signaling in skeletal muscle physiology and fibrosis

Hypoxia refers to the decrease in oxygen tension in the tissues, and the central effector of the hypoxic response is the transcription factor Hypoxia-Inducible Factor α (HIF1-α). Transient hypoxia in acute events, such as exercising or regeneration after damage, play an important role in skeletal muscle physiology and homeostasis. However, sustained activation of hypoxic signaling is a feature of skeletal muscle injury and disease, which can be a consequence of chronic damage but can also increase the severity of the pathology and worsen its outcome. Here, we review evidence that supports the idea that hypoxia and HIF-1α can contribute to the establishment of fibrosis in skeletal muscle through its crosstalk with other profibrotic factors, such as Transforming growth factor β (TGF-β), the induction of profibrotic cytokines expression, as is the case of Connective Tissue Growth Factor (CTGF/CCN2), or being the target of the Renin-angiotensin system (RAS).

Cross Talk with the GAR-3 Receptor Contributes to Feeding Defects in Caenorhabditis elegans eat-2 Mutants

Precise signaling at the neuromuscular junction (NMJ) is essential for proper muscle contraction. In the Caenorhabditis elegans pharynx, acetylcholine (ACh) released from the MC and M4 motor neurons stimulates two different types of contractions in adjacent muscle cells, termed pumping and isthmus peristalsis. MC stimulates rapid pumping through the nicotinic ACh receptor EAT-2, which is tightly localized at the MC NMJ, and eat-2 mutants exhibit a slow pump rate. Surprisingly, we found that eat-2 mutants also hyperstimulated peristaltic contractions, and that they were characterized by increased and prolonged Ca2+ transients in the isthmus muscles. This hyperstimulation depends on cross talk with the GAR-3 muscarinic ACh receptor as gar-3 mutation specifically suppressed the prolonged contraction and increased Ca2+ observed in eat-2 mutant peristalses. Similar GAR-3-dependent hyperstimulation was also observed in mutants lacking the ace-3 acetylcholinesterase, and we suggest that NMJ defects in eat-2 and ace-3 mutants result in ACh stimulation of extrasynaptic GAR-3 receptors in isthmus muscles. gar-3 mutation also suppressed slow larval growth and prolonged life span phenotypes that result from dietary restriction in eat-2 mutants, indicating that cross talk with the GAR-3 receptor has a long-term impact on feeding behavior and eat-2 mutant phenotypes.

Activity-Induced Increase in Achilles Tendon Blood Flow Is Age and Sex Dependent

BACKGROUND

Previous research of a young adult population identified a lower increase in Achilles tendon blood flow immediately after a running activity as a significant predictor for the development of Achilles tendinopathy (AT). Furthermore, advancing age is often mentioned as a risk factor for the development of AT, and the highest incidence for AT is reported to occur in middle-aged recreational male athletes.

PURPOSE

To investigate the effect of age, sex, and type of physical activity on the increase in Achilles tendon blood flow.

STUDY DESIGN

Controlled laboratory study.

METHODS

Blood flow measurements of 33 subjects aged 18 to 25 years and 30 subjects aged 40 to 55 years were obtained before and after 4 physical activities performed in randomized order: running, cycling, dynamic stretching, and rope skipping. Blood flow measurements of the Achilles tendon were performed before, immediately after, 5 minutes after, and 10 minutes after the physical activities. The effect of age, sex, and physical activities on the increase in blood flow was investigated with linear mixed models.

RESULTS

The results of this study identified that running, rope skipping, and cycling resulted in a significant increase in tendon blood flow ( P ≤ .001), whereas stretching did not. Prominent was the finding that the increase in blood flow after activity was significantly lower in the older population as compared with the younger population ( P < .001). Furthermore, male participants in the older group showed a significantly lower increase in tendon blood flow than did their female counterparts ( P = .019).

CONCLUSION

This study identified that sex and age significantly influence the increase in blood flow after activity, possibly explaining the increased risk for AT among middle-aged recreational athletes.

CLINICAL RELEVANCE

This study possibly identified one of the mechanisms explaining why an older male population is at increased risk for developing AT. Given that the lower increase in blood flow is an identified risk factor according to previous research, preventative measures should focus on improving this blood flow during physical activity in the physically active older male population. Registration: NCT03218605 ( ClinicalTrials.gov identifier).