Adaptation of Ion Channels in the Microcirculation to Exercise Training

Functional and structural adaptations of the coronary macro- and micro-vasculature to regular aerobic exercise by activation of physiological, cellular and molecular mechanisms: Esc Working Group on Coronary Pathophysiology & Microcirculation Position Paper

Regular aerobic exercise (RAEX) elicits several positive adaptations in all organs and tissues of the body, culminating in improved health and well-being. Indeed, in over half a century, many studies have shown the benefit of RAEX on cardiovascular outcome in terms of morbidity and mortality. RAEX elicits a wide range of functional and structural adaptations in the heart and its coronary circulation, all of which are to maintain optimal myocardial oxygen and nutritional supply during increased demand. Although there is no evidence suggesting that oxidative metabolism is limited by coronary blood flow (CBF) rate in the normal heart even during maximal exercise, increased CBF and capillary exchange capacities have been reported. Adaptations of coronary macro- and microvessels include outward remodeling of epicardial coronary arteries, increased coronary arteriolar size and density, and increased capillary surface area. In addition, there are adjustments in the neural and endothelial regulation of coronary macrovascular tone. Similarly, there are several adaptations at the level of microcirculation, including enhanced smooth muscle dependent pressure-induced myogenic constriction and upregulated endothelium-dependent flow-/shear-stress-induced dilation, increasing the range of diameter change. Alterations in the signaling interaction between coronary vessels and cardiac metabolism have also been described. At the molecular and cellular level, ion channels are key players in the local coronary vascular adaptations to RAEX, with enhanced activation of influx of Ca2+ contributing to the increased myogenic tone (via voltage gated Ca2+ channels) as well as the enhanced endothelium-dependent dilation (via TRPV4 channels). Finally, RAEX elicits a number of beneficial effects on several hemorheological variables that may further improve CBF and myocardial oxygen delivery and nutrient exchange in the microcirculation by stabilizing and extending the range and further optimizing the regulation of myocardial blood flow during exercise. These adaptations also act to prevent and/or delay the development of coronary and cardiac diseases.

Vascular cell transcriptomic changes to exercise training differ directionally along and between skeletal muscle arteriolar trees

EXT-induced arteriolar adaptations in skeletal muscle are heterogeneous because of spatial variations in muscle fiber type composition and fiber recruitment patterns during exercise. The purpose of this report is to summarize a series of experiments conducted to test the hypothesis that changes in vascular gene expression are signaled by alterations in shear stress resulting from increases in blood flow, muscle fiber type composition, and fiber recruitment patterns. We also report results from a follow-up study of Ankrd23, one gene whose expression was changed by EXT. We expected to see differences in magnitude of changes in gene expression along arteriolar trees and between/among arteriolar trees but similar directional changes. However, transcriptional profiles of arterioles/arteries from OLETF rats exposed to END or SIT reveal that EXT does not lead to similar directional changes in the transcriptome among arteriolar trees of different skeletal muscles or along arteriolar trees within a particular muscle. END caused the most changes in gene expression in 2A arterioles of soleus and white gastrocnemius with little to no changes in the FAs. Ingenuity Pathway Analysis across vessels revealed significant changes in gene expression in 18 pathways. EXT increased expression of some genes (Shc1, desert hedgehog protein (Dhh), adenylate cyclase 4 (Adcy4), G protein-binding protein, alpha (Gnat1), and Bcl2l1) in all arterioles examined, but decreased expression of ubiquitin D (Ubd) and cAMP response element modulator (Crem). Many contractile and/or structural protein genes were increased by SIT in the gastrocnemius FA, but the same genes exhibited decreased expression in red gastrocnemius arterioles. Ankrd23 mRNA levels increased with increasing branch order in the gastrocnemius arteriolar tree and were increased 19-fold in gastrocnemius muscle FA by SIT. Follow-up experiments indicate that Ankrd23 mRNA level was increased 14-fold in cannulated gastrocnemius FA when intraluminal pressure was increased from 90 and 180 cm H2O for 4 hours. Also, Ankrd23^-/- mice exhibit limited ability to form collateral arteries following femoral artery occlusion compared to WT mice (angioscore WT=0.18±0.03; Ankrd23^-/- =0.04±0.01). Further research will be required to determine whether Ankrd23 plays an important role in mechanically induced vascular remodeling of the arterial tree in skeletal muscle.

Physical activity-induced remodeling of vasculature in skeletal muscle: role in treatment of type 2 diabetes

This manuscript summarizes and discusses adaptations of skeletal muscle vasculature induced by physical activity and applies this understanding to benefits of exercise in prevention and treatment of type 2 diabetes (T2D). Arteriolar trees of skeletal muscle are heterogeneous. Exercise training increases capillary exchange and blood flow capacities. The distribution of vascular adaptation to different types of exercise training are influenced by muscle fiber type composition and fiber recruitment patterns that produce different modes of exercise. Thus training-induced adaptations in vascular structure and vascular control in skeletal muscle are not homogeneously distributed throughout skeletal muscle or along the arteriolar tree within a muscle. Results summarized indicate that similar principles apply to vascular adaptation in skeletal muscle in T2D. It is concluded that exercise training-induced changes in vascular gene expression differ along the arteriolar tree and by skeletal muscle fiber type composition. Results suggest that it is unlikely that hemodynamic forces are the only exercise-induced signals mediating the regulation of vascular gene expression. In patients with T2D, exercise training is perhaps the most effective treatment of the many related symptoms. Training-induced changes in the vasculature and in insulin signaling in the muscle fibers and vasculature augment glucose and insulin delivery as well as glucose uptake. If these adaptations occur in a sufficient amount of muscle mass, exposure to hyperglycemia and hyperinsulinemia will decrease along with the risk of microvascular complications throughout the body. It is postulated that exercise sessions in programs of sufficient duration, that engage as much skeletal muscle mass as possible, and that recruit as many muscle fibers within each muscle as possible will produce the greatest benefit. The added benefit of combined resistance and aerobic training programs and of high-intensity exercise programs is not simply "more exercise is better".

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Influence of Vascular Oxidative Stress and Inflammation on the Development and Progression of Atherosclerosis

Cardiovascular disease (CVD) risk factors such as hypertension, diabetes, dyslipidemia, smoking, physical inactivity, and obesity increase production of vascular reactive oxygen species (ROS), which results in a reduction of bioavailable nitric oxide and ultimately endothelial dysfunction and endothelial cell activation. ROS appears to mediate the inflammatory pathways that participate in the development and progression of atherosclerosis. There are numerous markers of oxidative stress and inflammation available for assessing the therapeutic response to interventions, but few are currently recommended for clinical use. Exercise training improves endothelial function via several mechanisms, including increased endothelial nitric oxide synthase—nitric oxide (eNOS-NO)— mediated production, increased activity and amount of antioxidants, attenuated ROS production, and an apparent reduction in systemic inflammation, possibly related to an increase in myokines resulting from skeletal muscle activation. Dietary antioxidant supplementation may improve endothelial function, oxidative stress, and inflammation, but much controversy exists regarding the use of antioxidant supplementation in primary and secondary CVD prevention. The purpose of this article is to review the contribution of vascular oxidative stress and activation of the inflammatory pathways in the pathogenesis of CVD and to review common methods used in clinical research to assess vascular oxidative stress and inflammation in response to therapeutic lifestyle interventions.

Gender influences coronary L-type Ca(2+) current and adaptation to exercise training in miniature swine

Endurance exercise training increases smooth muscle L-type Ca(2+) current density in both resistance and proximal coronary arteries of female miniature swine. The purpose of the present study was to determine 1) whether gender differences exist in coronary smooth muscle (CSM) L-type Ca(2+) current density and 2) whether endurance training in males would demonstrate a similar adaptive response as females. Proximal, conduit (approximately 1.0 mm), and resistance [~200 microm (internal diameter)] coronary arteries were obtained from sedentary and treadmill-trained swine of both sexes. CSM were isolated by enzymatic digestion (collagenase plus elastase), and voltage-gated Ca(2+)-channel current (I(Ca)) was determined by using whole cell voltage clamp during superfusion with 75 mM tetraethylammonium chloride and 10 mM BaCl(2). Current-voltage relationships were obtained at test potentials from -60 to 70 mV from a holding potential of -80 mV, and I(Ca) was normalized to cell capacitance (pA/pF). Endurance treadmill training resulted in similar increases in heart weight-to-body weight ratio, endurance time, and skeletal muscle citrate synthase activity in male and female swine. I(Ca) density was significantly greater in males compared with females in both conduit (-7.57 +/- 0.58 vs. -4.14 +/- 0.47 pA/pF) and resistance arteries (-11.25 +/- 0.74 vs. -6.49 +/- 0.87 pA/pF, respectively). In addition, voltage-dependent activation of I(Ca) in resistance arteries was shifted to more negative membrane potentials in males. Exercise training significantly increased I(Ca) density in both conduit and resistance arteries in females (-7.01 +/- 0.47 and -9.73 +/- 1.13 pA/pF, respectively) but had no effect in males (-8.61 +/- 0.50 and -12.04 +/- 1.07 pA/pF, respectively). Thus gender plays a significant role in determining both the magnitude and voltage dependence of I(Ca) in CSM and the adaptive response of I(Ca) to endurance training.