Lijun Shi

Aerobic exercise increases BKCa channel contribution to regulation of mesenteric arterial tone by upregulating β1‐subunit

•u2002 What is the central question of this study? Calcium‐activated K channels (BK) play critical roles in regulating cellular excitability and vascular tone. Exercise‐training has beneficial effects on cardiovascular diseases which may result from an improvement of the vascular functions. However, the molecular targets and mechanisms underlying this action remain largely unknown in peripheral resistance arteries. This paper asks the question, do BK channels play a role in bringing about these changes? •u2002 What is the main finding and its importance? This investigation is the first to demonstrate that aerobic exercise training increases the contribution of BK channels to regulation of vascular tone in mesenteric arteries. We found that it is mediated by upregulation of the Beta‐1 but not alpha1‐subunit protein to increase BK channel activity.

Chronic exercise normalizes changes in Cav1.2 and KCa1.1 channels in mesenteric arteries from spontaneously hypertensive rats

Regular physical activity is an effective non‐pharmacological therapy for prevention and control of hypertension. However, the underlying mechanisms are not fully understood. Accumulating evidence shows that the elevated vascular tone in hypertension is a consequence of the ‘ion channel remodelling’ that occurs during sustained high BP. The present study investigated the effects of aerobic exercise on the electrical remodelling of L‐type Ca2+ (Cav1.2) and large‐conductance Ca2+‐activated K+ (KCa1.1) channels in mesenteric arteries (MAs) from spontaneously hypertensive rats (SHRs).

Aging decreases the contribution of MaxiK channel in regulating vascular tone in mesenteric artery by unparallel downregulation of α- and β1-subunit expression.

Vascular disease increases in incidence with age and is the commonest cause of morbidity and mortality among elderly people. Large-conductance Ca(2+)-activated K(+)(MaxiK) channel, with pore-forming α-subunit and modulatory β1-subunit, is a key regulator of vascular tone. This study explored functional and molecular evidence of MaxiK alteration with aging in the mesenteric artery(MA). Young, Middle-aged, and Old male Wistar rats were used. Selective MaxiK channel blocker (Iberiotoxin) induced a significant increase of vascular tension in MA in all three age groups. However, these effects were greatly decreased in Old animals. The amplitude and frequency of spontaneous transient outward currents were significantly decreased with aging. Single channel recording revealed that aging induced a decrease of the open probability and the mean open time, but an increase of the mean closed time of MaxiK channel. The Ca(2+)/voltage sensitivity of MaxiK was also decreased. Western blotting showed that the protein expression of MaxiK β1- and α-subunit was significantly reduced with aging, and the suppression of β1 subunits was larger than that of α subunits. These data suggest that aging decreases capability of MaxiK channel in regulating vascular tone in the MA, which may be partially mediated by unparallel downregulation of α- and β1-subunit expression.

Effect of exercise training volume on arterial contractility and BKCa channel activity in rat thoracic aorta smooth muscle cells

Large-conductance Ca2+-activated K+ (BKCa) channels play a critical role in regulating cellular excitability and vascular tone. Exercise training showed reversible beneficial effects on cardiovascular systems with an improvement of vascular functions. This study investigated the effects of exercise training volume on vascular function and BKCa channel activity in thoracic aorta smooth muscle cells (SMCs) in 20 sedentary (SED) and 40 training rats, submitted to a treadmill training protocol (20xa0m/min, 60xa0min/day, 12xa0weeks). Training rats were divided into two groups, exercising 3xa0days/week (EX1) and 5xa0days/week (EX2). Since intensity and duration of exercise were identical between training groups, the training volume was higher in EX2 than in EX1. Exercise training not only decreased heart rate, but also attenuated pressor responses induced by angiotensin II or norepinephrine (NE). The maximal vascular contraction induced by 10−5xa0M NE was significantly decreased after training. In precontracted thoracic aorta with NE (10−5xa0M), activation of the BKCa channels by NS1619 significantly decreased the tension. The sensitivity of tissue to NS619 (pD2) was significantly correlated with volume of training (SEDxa0<xa0EX1xa0<xa0EX2). Inside-out patch clamp recording on aortic SMCs showed that exercise training significantly increased the open probability, decreased the mean closed time and increased the mean open time of BKCa channels. This effect was more significant in the EX2 group than in the EX1 group. These data suggest that there is a dose effect for exercise training volume for the activation of BKCa channels in vascular SMCs, which contributes to improvement of the arterial function in thoracic aortas.

Exercise intensity-dependent reverse and adverse remodeling of voltage-gated Ca 2+ channels in mesenteric arteries from spontaneously hypertensive rats

Exercise can be regarded as a drug for treating hypertension, and the ‘dosage’ (intensity/volume) is therefore of great importance. L-type voltage-gated Ca2+ (Cav1.2) channels on the plasma membrane of vascular smooth muscle cells have a pivotal role in modulating the vascular tone, and the upregulation of Cav1.2 channels is a hallmark feature of hypertension. The present study investigated the beneficial and adverse effects of exercise at different intensities on the remodeling of the Cav1.2 channel in mesenteric arteries (MAs) of spontaneously hypertensive rats (SHRs). Moderate- (SHR-M, 18–20u2009mu2009min−1) and high-intensity (SHR-H, 26–28u2009mu2009min−1) aerobic exercise training groups were created for SHRs and lasted for 8 weeks (1u2009h per day, 5 d per week). Age-matched sedentary SHRs and normotensive Wistar–Kyoto rats (WKY) were used as controls. The mesenteric arterial mechanical and functional properties were evaluated. Moderate-intensity exercise training induced a lower systolic blood pressure and heart rate in these rats compared with sedentary SHRs. BayK 8644 and nifedipine induced vasoconstriction and dose-dependent vasorelaxation, respectively, in the mesenteric arterial rings. Moderate-intensity exercise significantly suppressed the increase in BayK 8644-induced vasoconstriction, tissue sensitivity to nifedipine, Cav1.2 channel current density and Cav1.2 α1C-subunit protein expression in MAs from SHRs. However, high-intensity exercise training aggravated all of these hypertension-associated functional and molecular alterations of Cav1.2 channels. These results indicate that moderate-intensity aerobic training may act as a drug and effectively reverse the remodeling of Cav1.2 channels in hypertension to restore the vascular function in MAs, but that high-intensity exercise exaggerates the adverse remodeling of Cav1.2 channels and worsens the vascular function.

Effects of aerobic exercise training on large-conductance Ca 2+ -activated K + channels in rat cerebral artery smooth muscle cells

PurposeLarge-conductance Ca2+-activated K+ (BKCa) channels provide a negative feedback that regulates vascular tone in the brain circulation. This study investigated the effects of aerobic exercise on gating properties of BKCa channels in rat cerebral artery.MethodsRats were subjected to moderate-intensity exercise at low (EX-3d/w) and high (EX-5d/w) training volume on a motor-driven treadmill, and compared with age-matched sedentary animals (SED). Inside–out (I/O) patch clamp recording was performed to measure gating properties of the BKCa channel.ResultsAerobic exercise induced a reduction in heart rate and body weight in both training groups. Exercise increased the channel activity, which was more pronounced in EX-5d/w than that in EX-3d/w group. Kinetic analysis revealed that (1) the contribution of short open states was elevated and the duration of both short and long open states were extended by exercising in EX-3d/w; (2) Ex-3d/w had no significant change on conformation of close states; (3) EX-3d/w increased the mean open time without changing mean closed time; (4) EX-5d/w increased both the contribution and duration of long open states; (5) EX-5d/w increased channel mean open time while decreased mean closed time.ConclusionThe results suggest that regular aerobic exercise may enhance BKCa channel activity in cerebral arterial myocytes by changing its biophysical properties, and the electrical remolding induced by exercise may be training volume-dependent.

Epigenetic regulation of L-type voltage-gated Ca 2+ channels in mesenteric arteries of aging hypertensive rats

Accumulating evidence has shown that epigenetic regulation is involved in hypertension and aging. L-type voltage-gated Ca2+ channels (LTCCs), the dominant channels in vascular myocytes, greatly contribute to arteriole contraction and blood pressure (BP) control. We investigated the dynamic changes and epigenetic regulation of LTCC in the mesenteric arteries of aging hypertensive rats. LTCC function was evaluated by using microvascular rings and whole-cell patch-clamp in the mesenteric arteries of male Wistar-Kyoto rats and spontaneously hypertensive rats at established hypertension (3 month old) and an aging stage (16 month old), respectively. The expression of the LTCC α1C subunit was determined in the rat mesenteric microcirculation. The expression of miR-328, which targets α1C mRNA, and the DNA methylation status at the promoter region of the α1C gene (CACNA1C) were also determined. In vitro experiments were performed to assess α1C expression after transfection of the miR-328 mimic into cultured vascular smooth muscle cells (VSMCs). The results showed that hypertension superimposed with aging aggravated BP and vascular remodeling. Both LTCC function and expression were significantly increased in hypertensive arteries and downregulated with aging. miR-328 expression was inhibited in hypertension, but increased with aging. There was no significant difference in the mean DNA methylation of CACNA1C among groups, whereas methylation was enhanced in the hypertensive group at specific sites on a CpG island located upstream of the gene promoter. Overexpression of miR-328 inhibited the α1C level of cultured VSMCs within 48u2009h. The results of the present study indicate that the dysfunction of LTCCs may exert an epigenetic influence at both pre- and post-transcriptional levels during hypertension pathogenesis and aging progression. miR-328 negatively regulated LTCC expression in both aging and hypertension.

Exercise Training Reverses Unparallel Downregulation of MaxiK Channel α- and β1-Subunit to Enhance Vascular Function in Aging Mesenteric Arteries

This study was designed to determine the effects of aerobic exercise training on aging-associated selective changes of the function and expression of the large-conductance Ca(2+)-activated K(+) (MaxiK) channels in mesenteric arteries. Male Wistar rats aged 19-21 months were randomly assigned to sedentary (O-SED) and exercise-trained groups (O-EX). Two-month-old rats were used as Young control. Addition of iberiotoxin (10(-8) M) increased the norepinephrine-induced arterial contraction in all three groups, with the greatest enhancement being in Young and the least in O-SED. Patch clamp study revealed the characteristics of aging on MaxiK channel function in mesenteric arteries, mainly including (a) decrease of iberiotoxin-sensitive whole-cell K(+) current, (b) decrease of open probability and Ca(2+)/voltage sensitivity of single MaxiK channel, and (c) reduction of tamoxifen-induced MaxiK activation. After exercise training, all of these changes were markedly inhibited. Western blotting revealed that the protein expression of MaxiK was significantly reduced with aging and the suppression of β1-subunit was larger than that of α-subunit, although exercise training diminished this alteration. Taken together, aerobic exercise training reverses the aging-related unparallel downregulation of MaxiK α- and β1-subunit expression on mesenteric arteries, which partly underlies the beneficial effect of exercise on restoring aging-associated reduction in mesenteric artery vasodilatory properties.

Exercise Prevents Upregulation of RyRs-BKCa Coupling in Cerebral Arterial Smooth Muscle Cells From Spontaneously Hypertensive Rats.

Objective—Regular exercise is an effective nonpharmacological means of preventing and controlling hypertension. However, the molecular mechanisms underlying its effects remain undetermined. The hypothesis that hypertension increases the functional coupling of large-conductance Ca2+-activated K+ (BKCa) channels with ryanodine receptors in spontaneously hypertensive rats (SHR) as a compensatory response to an increase in intracellular Ca2+ concentration in cerebral artery smooth muscle cells was assessed here. It was further hypothesized that exercise training would prevent this increase in functional coupling. Approach and Results—SHR and Wistar–Kyoto (WKY) rats were randomly assigned to sedentary groups (SHR-SED and WKY-SED) and exercise training groups (SHR-EX and WKY-EX). Cerebral artery smooth muscle cells displayed spontaneous transient outward currents at membrane potentials more positive than −40 mV. The amplitude of spontaneous transient outward currents together with the spontaneous Ca2+ sparks in isolated cerebral artery smooth muscle cells was significantly higher in SHR-SED than in WKY-SED. Moreover, hypertension displayed increased whole-cell BKCa, voltage-gated Ca2+ channel, but decreased KV currents in cerebral artery smooth muscle cells. In SHRs, the activity of the single BKCa channel increased markedly, and the protein expression of BKCa (&bgr;1, but not &agr;-subunit) also increased, but KV1.2 decreased significantly. Exercise training ameliorated all of these functional and molecular alterations in hypertensive rats. Conclusions—These data indicate that hypertension leads to enhanced functional coupling of ryanodine receptors–BKCa to buffer pressure–induced constriction of cerebral arteries, which attributes not only to an upregulation of BKCa &bgr;1-subunit function but also to an increase of Ca2+ release from ryanodine receptors. However, regular aerobic exercise efficiently prevents augmented coupling and so alleviates the pathological compensation and restores cerebral arterial function.

Akt modulation by miR-145 during exercise-induced VSMC phenotypic switching in hypertension.

Aims: This study investigated whether long‐term exercise can influence vascular smooth muscle cells (VSMCs) phenotypic switching in mesenteric arteries of hypertensive rats, with a focus on the modulation of protein kinase B (PKB/Akt) signaling by microRNA‐145 (miR‐145). Main methods: In the exercise intervention experiment, mesenteric arteries from 3‐month‐old spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were isolated for histological observation, phenotypic marker analysis, Akt phosphorylation quantification, and miR‐145 evaluation after being subjected to moderate‐intensity treadmill training (E) or being sedentary (C) for 8 weeks. In the transfection experiment, VSMCs were harvested to determine Akt phosphorylation and mRNA expressions of the upstream and downstream signaling molecules. Key findings: Calponin, a VSMC contractile marker, was significantly up‐regulated in SHR‐E relative to SHR‐C (P < 0.05); while osteopontin (OPN), a dedifferentiation marker, was down‐regulated in SHR‐E relative to SHR‐C (P < 0.05). Exercise significantly normalized the expression of miR‐145 and significantly enhanced Akt phosphorylation (P < 0.05). In VSMCs over‐expressing miR‐145, Akt phosphorylation was significantly decreased (P < 0.05) with inhibited mRNA of both insulin‐like growth factor 1 receptor (IGF‐1R) and insulin receptor substrate 1 (IRS‐1). In VSMCs transfected with miR‐145 inhibitor, Akt phosphorylation and mRNA of IGF‐1R and IRS‐1 were all down‐regulated. miR‐145 did not exhibit a clear effect on p70 ribosomal kinase (p70S6K), the downstream of Akt, following the transfections. Significance: Overall, exercise remodels arterioles in hypertension and induces VSMCs maintaining contractile phenotype, in which miR‐145 appears to be involved by inversely regulating Akt signaling via its upstream signals.