慢性吸烟大鼠肺动脉平滑肌细胞钾通道Kv1.5、BKCa表达的变化

目的：观察吸烟对大鼠肺动脉平滑肌大电导的钙激活的钾通道（BK_Ca）和电压依赖性延迟整流钾通道Kv1.5蛋白和mRNA表达的影响，以阐明吸烟引起的肺血管反应性改变中钾通道表达的变化。方法：复制大鼠的慢性吸烟模型，采用HE染色、免疫组织化学染色、原位杂交等方法。结果：（1）慢性吸烟可降低大鼠肺动脉平滑肌 BK_Ca 蛋白和mRNA表达；（2）慢性吸烟可降低大鼠肺动脉平滑肌Kv1.5蛋白和mRNA表达；（3）大动脉 BK_Ca的降低程度大于Kv1.5，小动脉 BK_Ca和Kv1.5的降低程度无明显差异。结论：慢性吸烟可下调大鼠肺动脉平滑肌钾通道 BK_Ca和Kv1.5的表达水平，是导致肺血管反应性增高的机制之一。     

噻庚啶和山莨菪碱拮抗TNFα诱导的内皮细胞[Ca2+]i增高

目的：研究噻庚啶（Cyp）和山莨菪碱（Ani）对肿瘤坏死因子（TNFα）诱导单个内皮细胞内Ca²⁺浓度（[Ca²⁺]_i）变化的影响，以探TNFα介导休克和Cyp、Ani的抗休克的机制。方法：人脐静脉内皮细胞株（ECV304）接种于35 mm含2 mL DMEM培养基的组织培养盘中培养。Fluo-3/AM负载细胞，激光扫描共聚焦显微技术（LSCM）测定单个内皮细胞[Ca²⁺]_i。结果：TNFα使单个内皮细胞[Ca²⁺]_i呈剂量依赖性升高，在60 s内达到峰值，然后下降并保持在基础水平之上。共聚焦扫描图像显示细胞核区[Ca²⁺]_i升高比胞浆区明显，下降比胞浆区慢。Cyp（3×10^-5 mol/L或6×10^-5 mol/L）、Ani（2×10^-5 mol/L或4×10^-5 mol/L）均能显著抑制由TNFα（1.2×10^-9 mol/L）诱导的单个内皮细胞[Ca²⁺]_i升高。结论：TNFα诱导内皮细胞[Ca²⁺]_i升高可能是TNFα介导休克的重要机制；Cyp和Ani抑制TNFα诱导的[Ca²⁺]_i升高可能是其抗休克作用的机制之一。     

一氧化氮在失血性休克再灌注损伤中的作用及牛磺酸的影响

目的:探讨一氧化氮(NO)在失血性休克再灌注损伤中的作用及牛磺酸的影响。方法:新西兰种兔24只随机分为3组(n=8):对照组、休克组、牛磺酸治疗组。采用失血性休克-再灌注损伤模型。连续观察休克前、休克1.5h、再灌注1h、2h、3h时血浆一氧化氮合酶(NOS)活性、一氧化氮代谢产物(NO^-₂／NO^-₃)含量、超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量、乳酸脱氢酶(LDH)活性的动态变化。结果:①休克组再灌注各时限血浆NOS活性、NO^-₂／NO^-₃含量、MDA含量、LDH活性显著高于休克前及休克1.5h;SOD活性显著低于休克前及休克1.5h。②休克组再灌注3h时心、肺组织NOS活性、NO^-₂／NO^-₃含量、MDA含量显著高于对照组;SOD活性显著低于对照组。③牛磺酸(40mg·kg^-1, iv)可减轻再灌注各时限上述指标的变化。④血浆、心肺组织中NO^-₂／NO^-₃含量与MDA含量均呈正相关。结论:NO介导了休克再灌注损伤, 大量释放的NO参与休克再灌注损伤的脂质过氧化反应, 牛磺酸的拮抗作用可能与减少NO的生成、抗脂质过氧化有关。     

慢性低氧对肺动脉内皮及平滑肌细胞急性低氧时胞浆游离钙变化的影响

目的和方法:以Fura-2/AM荧光指示剂负载,检测常氧(PO2213kPa)及慢性低氧[PO2(53±07)kPa]培养的大鼠肺内动脉平滑肌细胞及猪肺动脉内皮细胞胞浆游离钙的水平及其对急性低氧刺激反应的变化。结果:慢性低氧条件培养的第6代肺内动脉平滑肌细胞在急性低氧时[Ca²⁺]_i升高的程度明显降低(P<0.05);而慢性低氧条件培养的第5代肺动脉内皮细胞对急性低氧引起的[Ca²⁺]_i升高程度明显增加(P<0.05)。结论:慢性低氧可以减弱肺内动脉平滑肌细胞对急性低氧所致[Ca²⁺]_i升高的反应而增强肺动脉内皮细胞低氧性[Ca²⁺]_i升高的反应。这可能在慢性低氧时肺血管对低氧的反应性降低中起重要作用。     

拉马克啉对缺氧培养的肺动脉内皮及平滑肌细胞的影响及其机制探讨

目的:探讨三磷酸腺苷(ATP)敏感钾通道开放剂拉马克啉(Lev)对缺氧条件下培养的肺动脉内皮(PAEC)及平滑肌细胞(PASMC)的影响及其可能的作用机制。方法:分析Lev对缺氧条件下培养的PAEC及PASMC的[Ca²⁺]_i、上清液中NO^-₂及ET-1水平、细胞内PKC_α、eNOS、iNOS及PDGF-B的mRNA和蛋白质水平及PASMC增殖和凋亡的影响及其作用的细胞内机制。结果:①Lev可降低缺氧时PASMC及PAEC上清液中ET-1及细胞内PKC_α、iNOS及PDGF-B的mRNA和蛋白质水平,可降低PASMC[Ca²⁺]_i,抑制PASMC增殖,促其凋亡(P均<0.05),而对PAEC[Ca²⁺]_i及PASMC、PAEC上清液中NO^-₂水平及细胞内eNOS的mRNA和蛋白质水平无明显影响(P均>0.05)。②Lev下调缺氧时PASMC及PAEC上清液中ET-1水平及PASMC增殖的机制涉及抑制缺氧时PKC_α信号通道的功能活性。结论:Lev可减轻缺氧对PAEC及PASMC的某些不利影响,其作用的部分机制涉及下调缺氧时PAEC及PASMC内PKC_α信号通道的功能活性和降低PASMC的[Ca²⁺]_i,而与eNOS-NO信号通道无关。     

雌激素通过KATP通道影响大鼠肠系膜动脉的反应性

目的: 观察雌激素对大鼠肠系膜动脉平滑肌ATP敏感性钾离子通道 (K_ATP 通道)mRNA表达的影响,探讨K_ATP通道在雌激素调节大鼠肠系膜血管反应性中的作用。方法: 雌性SD大鼠48只,体重(100±10) g,随机分为假手术组(sham)、卵巢切除组(Ovx)和卵巢切除后补充雌激素组(Ovx +E)。采取实时荧光定量PCR检测大鼠肠系膜动脉中K_ATP通道mRNA的表达;观察各组大鼠肠系膜动脉对去甲肾上腺素(NE)升压效应的反应性。结果: 与sham组相比,Ovx组大鼠肠系膜动脉K_ATP 通道的Kir6.1及SUR2B亚单位mRNA表达减少(P<0.05),而Ovx+E组则表达增加(P<0.05)。与sham组相比,Ovx组大鼠的血管反应性明显增加(P<0.05),Ovx+E组无明显差异。给予K_ATP通道阻滞剂格列本脲后,sham组和Ovx+E组的动脉反应性增加(P<0.05),Ovx组无明显变化(P>0.05),此时3组间比较无明显差异(P>0.05)。结论: 雌激素可能通过上调肠系膜动脉平滑肌细胞K_ATP通道的表达来降低动脉对去甲肾上腺素升压效应的反应性。     

失血性休克大鼠血管平滑肌收缩功能变化研究

目的：研究失血性休克后大鼠胸主动脉血管平滑肌收缩功能变化并初步探讨其可能机制。方法：采用生物张力换能器及生理记录仪等技术体外测定失血性休克大鼠在休克后2 h、4 h VSM环对去甲肾上腺素（NE）、苯肾上腺素（PE）、咖啡因（caffeine）及氯化钾（KCl）等的收缩反应张力。结果：VSM环在休克后2 h、4 h对NE的最大反应张力分别为对照组的76.17%和66.50%；休克2 h后对高浓度（大于20 mmol/L）K⁺ 和20 mmol/L caffeine的反应张力明显下降；休克后4 h对 3×10^-6 mol/L PE的反应张力亦显著下降。结论：失血性休克后大鼠VSM收缩功能下降，反应性降低，其初步机制可能部分与休克后VSM细胞胞外钙内流及胞内钙释放功能下降等有关。     

K+通道在正常与慢性低氧大鼠低氧性肺血管收缩反应中的作用

目的:探讨K⁺通道在慢性低氧致低氧性肺血管收缩反应降低中的作用。方法:采用离体肺灌流实验,研究4-AP(4-aminopyridine,电压依赖性K⁺通道-Kv阻滞剂)、TEA(tetraethylamonium,Ca²⁺激活性K⁺通道-K_Ca阻滞剂)、GLIB(glibenclamide,ATP敏感性K⁺通道-K_ATP阻滞剂)对正常与慢性低氧大鼠肺血管低氧反应的影响。结果:4-AP、TEA均可使正常大鼠肺动脉基础压上升,且使其肺血管低氧反应明显增强;对于慢性低氧大鼠,其肺血管对低氧反应明显低下,4-AP、TEA升肺动脉基础压的作用明显低于对照鼠肺,GLIB也呈现升高肺动脉基础压力作用,4-AP、TEA、GLIB均可使肺血管低氧反应大大增强,增强的比例明显大于正常对照组。结论:在离体灌流鼠肺HPV中,Kv、K_Ca的开放起调节作用,大鼠经慢性低氧后,肺血管反应性明显降低,可能与Kv、K_Ca、K_ATP在HPV中的调节作用相对增强有关。     

尿激酶和链激酶对大鼠血小板功能的影响

目的：观察尿激酶（UK）和链激酶（SK）是否能直接激活血小板。方法：在体外制备大鼠血小板，以血小板聚集、血小板释放丙二醛（MDA）及5-羟色胺（5-HT）、血小板内游离钙（[Ca²⁺]_i）为指标，观察UK和SK对血小板的直接作用；在体内观察它们对电刺激诱导大鼠动脉形成血栓的影响。结果：在体外2×10⁶ U/L的UK与SK对凝血酶及ADP诱导的血小板聚集、对凝血酶诱导的血小板释放MDA含量、5-HT含量和血小板[Ca²⁺]_i无明显影响。在体内4×10⁴ U/kg的UK和SK对电刺激诱导的大鼠动脉血栓形成有一定的抑制作用。结论：UK和SK不能直接激活血小板。     

内源性血管紧张素Ⅱ对大鼠血管钙化的作用

目的:在大鼠血管钙化模型上观察内源性血管紧张素II(AngⅡ)对大鼠血管钙化的影响。方法:用VitD₃皮下注射和尼古丁灌胃诱导大鼠血管钙化模型。测定血管组织中钙含量、[⁴⁵Ca²⁺]聚集及碱性磷酸酶活性作为观察钙化的指标。结果:钙化血管组织中钙含量,[⁴⁵Ca²⁺]摄入及碱性磷酸酶活性分别高于对照组。血管组织中的血管紧张素原mRNA、血浆和血管AngⅡ含量均高于对照组水平。血管紧张素转换酶抑制剂卡托普利和AngⅡ受体AT₁阻断剂洛沙坦处理的大鼠血管内钙含量、[⁴⁵Ca²⁺]聚集及碱性磷酸酶活性显著低于单纯钙化组。卡托普利处理的钙化大鼠血浆和动脉中AngⅡ含量、动脉中血管紧张素原mRNA的含量也显著低于钙化组水平。结论:钙化大鼠血浆和血管组织中AngⅡ水平上调,卡托普利和洛沙坦可减轻大鼠血管钙化程度。     

缺血预处理对失血性休克大鼠血管反应性及钙敏感性的影响

目的：观察缺血预处理对失血性休克血管反应性和钙敏感性的影响。方法：通过观察不同缺血预处理方法对失血性休克大鼠存活时间和24 h存活率的影响,选择最适缺血预处理方法。在体实验,观察缺血预处理对失血性休克大鼠肠系膜上动脉（SMA）血管管径对去甲肾上腺素（NE）收缩反应性和NE升压反应的影响;离体实验,应用离体血管环张力测定技术,观察缺血预处理对失血性休克后大鼠SMA环血管反应性和钙敏感性的影响。结果：确定最适缺血预处理方法为：夹闭腹主动脉1 min,开放5 min,重复3次,2 h后复制失血性休克模型,这种方法可显著增加失血性休克大鼠的存活时间和24 h存活率。在体实验,缺血预处理可显著增加休克晚期NE的升压效应和在体SMA对NE的收缩反应（P<0.01）。离体实验,与失血性休克对照组比较,缺血预处理组SMA在休克早期(休克即刻)对NE的收缩反应性和钙敏感性明显下降（P<0.05）,但与正常对照组比较无显著差异（P>0.05）;在休克后期（休克2 h、3 h、4 h）,缺血预处理组SMA对NE的收缩反应性和钙敏感性显著增加（P<0.05）,且与正常对照组比较无显著差异（P>0.05）。结论：缺血预处理可能通过改善血管钙敏感性发挥对休克后期血管反应性的保护效应。     

Myosin light chain kinase is necessary for post-shock mesenteric lymph drainage enhancement of vascular reactivity and calcium sensitivity in hemorrhagic-shocked rats

Vascular hyporeactivity is an important factor in irreversible shock, and post-shock mesenteric lymph (PSML) blockade improves vascular reactivity after hemorrhagic shock. This study explored the possible involvement of myosin light chain kinase (MLCK) in PSML-mediated vascular hyporeactivity and calcium desensitization. Rats were divided into sham (n=12), shock (n=18), and shock+drainage (n=18) groups. A hemorrhagic shock model (40±2 mmHg, 3 h) was established in the shock and shock+drainage groups. PSML drainage was performed from 1 to 3 h from start of hypotension in shock+drainage rats. Levels of phospho-MLCK (p-MLCK) were determined in superior mesenteric artery (SMA) tissue, and the vascular reactivity to norepinephrine (NE) and sensitivity to Ca²⁺ were observed in SMA rings in an isolated organ perfusion system. p-MLCK was significantly decreased in the shock group compared with the sham group, but increased in the shock+drainage group compared with the shock group. Substance P (1 nM), an agonist of MLCK, significantly elevated the decreased contractile response of SMA rings to both NE and Ca²⁺ at various concentrations. Maximum contractility (E_max) in the shock group increased with NE (from 0.179±0.038 to 0.440±0.177 g/mg, P<0.05) and Ca²⁺ (from 0.515±0.043 to 0.646±0.096 g/mg, P<0.05). ML-7 (0.1 nM), an inhibitor of MLCK, reduced the increased vascular response to NE and Ca²⁺ at various concentrations in the shock+drainage group (from 0.744±0.187 to 0.570±0.143 g/mg in E_max for NE and from 0.729±0.037 to 0.645±0.056 g/mg in E_max for Ca²⁺, P<0.05). We conclude that MLCK is an important contributor to PSML drainage, enhancing vascular reactivity and calcium sensitivity in rats with hemorrhagic shock.     

Effects of aerobic exercise training on large-conductance Ca2+-activated K+ channels in rat cerebral artery smooth muscle cells

Purpose

Large-conductance Ca²⁺-activated K⁺ (BK_Ca) 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 BK_Ca channels in rat cerebral artery.

Methods

Rats 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 BK_Ca channel.

Results

Aerobic 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.

Conclusion

The results suggest that regular aerobic exercise may enhance BK_Ca channel activity in cerebral arterial myocytes by changing its biophysical properties, and the electrical remolding induced by exercise may be training volume-dependent.     

Involvement of large conductance Ca2+-activated K+ channel in laminar shear stress-induced inhibition of vascular smooth muscle cell proliferation

The large conductance Ca²⁺-activated K⁺ (BK_Ca) channel in vascular smooth muscle cell (VSMC) is an important potassium channel that can regulate vascular tone. Recent work has demonstrated that abnormalities in BK_Ca channel function are associated with changes in cell proliferation and the onset of vascular disease. However, until today there are rare reports to show whether this channel is involved in VSMC proliferation in response to fluid shear stress (SS). Here we investigated a possible role of BK_Ca channel in VSMC proliferation under laminar SS. Rat aortic VSMCs were plated in parallel-plate flow chambers and exposed to laminar SS with varied durations and magnitudes. VSMC proliferation was assessed by measuring proliferating cell nuclear antigen (PCNA) expression and DNA synthesis. BK_Ca protein and gene expression was determined by flow cytometery and RT-PCR. The involvement of BK_Ca in SS-induced inhibition of proliferation was examined by BK_Ca inhibition using a BK_Ca specific blocker, iberiotoxin (IBTX), and by BK_Ca transfection in BK_Ca non-expressing CHO cells. The changes in [Ca²⁺]_i were determined using a calcium-sensitive dye, fluo 3-AM. Membrane potential changes were detected with a potential-sensitive dye, DiBAC₄(3). We found that laminar SS inhibited VSMC proliferation and stimulated BK_Ca channel expression. Furthermore, laminar SS induced an increase in [Ca²⁺]_i and membrane hyperpolarization. Besides in VSMC, the inhibitory effect of BK_Ca channel activity on cell proliferation in response to SS was also confirmed in BK_Ca-transfected CHO cells showing a decline in proliferation. Blocking BK_Ca channel reversed its inhibitory effect, providing additional support for the involvement of BK_Ca in SS-induced proliferation reduction. Our results suggest, for the first time, that BK_Ca channel mediates laminar SS-induced inhibition of VSMC proliferation. This finding is important for understanding the mechanism by which SS regulates VSMC proliferation, and should be helpful in developing strategies to prevent flow-initiated vascular disease formation.     

阻断肠淋巴液回流提升失血性休克大鼠的血管反应性和钙敏感性

目的:观察肠淋巴管结扎或肠淋巴液引流对失血性休克(HS)大鼠血管反应性与钙敏感性的影响,探讨肠淋巴液在休克血管低反应性中的作用。方法:72只Wistar雄性大鼠随机均分为sham组(仅手术)、shock组(复制HS模型)、shock+ligation组(复制HS模型,行肠淋巴管结扎)、shock+drainage组(复制HS模型,行肠淋巴液引流)。记录所有动物在不同时点给予去甲肾上腺素(NE 3μg/kg)后平均动脉血压(MAP)的变化;维持低血压40 mmHg 3 h后,制备肠系膜上动脉(SMA)血管环(均n=36)。采用离体血管环张力测定技术,观察SMA血管环对NE反应性以及钙敏感性[梯度Ca2+、与血管紧张素Ⅱ(AngⅡ)、胰岛素(Ins)分别孵育]的变化。结果:Shock组在休克即刻和0.5 h△MAP显著高于sham组,在1.5 h、2 h、2.5 h、3 h均显著降低;shock+ligation和shock+drainage组在休克即刻、0.5 h、1 h时△MAP显著高于sham组,在2.5 h和3 h时显著降低;shock+ligation和shock+drainage组在休克0.5 h后多个时点的△MAP均显著高于shock组。Shock、shock+ligation和shock+drainage组SMA血管环对NE的反应性和Ca2+的敏感性均显著低于sham组;shock+ligation和shock+drainage组SMA血管环对NE的反应性和Ca2+的敏感性均高于shock组。SMA与AngⅡ或Ins孵育后,shock、shock+ligation和shock+drainage组血管反应性和钙敏性均显著低于sham组,且shock+ligation和shock+drainage组均显著高于shock组。结论:以肠淋巴管结扎或肠淋巴液引流阻断休克肠淋巴液回流,均可提高HS大鼠的血管反应性,其机制与提高钙敏感性有关。     

Ca2+-dependent large conductance K+ currents in thalamocortical relay neurons of different rat strains

Mutations in genes coding for Ca²⁺ channels were found in patients with childhood absence epilepsy (CAE) indicating a contribution of Ca²⁺-dependent mechanisms to the generation of spike-wave discharges (SWD) in humans. Since the involvement of Ca²⁺ signals remains unclear, the aim of the present study was to elucidate the function of a Ca²⁺-dependent K⁺ channel (BK_Ca) under physiological conditions and in the pathophysiological state of CAE. The activation of BK_Ca channels is dependent on both voltage and intracellular Ca²⁺ concentrations. Moreover, these channels exhibit an outstandingly high level of regulatory heterogeneity that builds the basis for the influence of BK_Ca channels on different aspects of neuronal activity. Here, we analyse the contribution of BK_Ca channels to firing of thalamocortical relay neurons, and we test the hypothesis that BK_Ca channel activity affects the phenotype of a genetic rat model of CAE. We found that the activation of the β₂-adrenergic receptor/protein kinase A pathway resulted in BK_Ca channel inhibition. Furthermore, BK_Ca channels affect the number of action potentials fired in a burst and produced spike frequency adaptation during tonic activity. The latter result was confirmed by a computer modelling approach. We demonstrate that the β₂-adrenergic inhibition of BK_Ca channels prevents spike frequency adaptation and, thus, might significantly support the tonic firing mode of thalamocortical relay neurons. In addition, we show that BK_Ca channel functioning differs in epileptic WAG/Rij and thereby likely contributes to highly synchronised, epileptic network activity.     

K+ channel modulation in arterial smooth muscle

Potassium channels play an essential role in the membrane potential of arterial smooth muscle, and also in regulating contractile tone. Four types of K⁺ channel have been described in vascular smooth muscle: Voltage-activated K⁺ channels (K_V) are encoded by the Kv gene family, Ca²⁺-activated K⁺ channels (BK_Ca) are encoded by the slogene, inward rectifiers (K_IR) by Kir2.0, and ATP-sensitive K⁺ channels (K_ATP) by Kir6.0 and sulphonylurea receptor genes. In smooth muscle, the channel subunit genes reported to be expressed are: Kv1.0, Kv1.2, Kv1.4–1.6, Kv2.1, Kv9.3, Kvβ1–β4, slo α and β, Kir2.1, Kir6.2, and SUR1 and SUR2. Arterial K⁺ channels are modulated by physiological vasodilators, which increase K⁺ channel activity, and vasoconstrictors, which decrease it. Several vasodilators acting at receptors linked to cAMP-dependent protein kinase activate K_ATP channels. These include adenosine, calcitonin gene-related peptide, and β-adrenoceptor agonists. β-adrenoceptors can also activate BK_Ca and K_V channels. Several vasoconstrictors that activate protein kinase C inhibit K_ATP channels, and inhibition of BK_Ca and K_V channels through PKC has also been described. Activators of cGMP-dependent protein kinase, in particular NO, activate BK_Ca channels, and possibly K_ATP channels. Hypoxia leads to activation of K_ATP channels, and activation of BK_Ca channels has also been reported. Hypoxic pulmonary vasoconstriction involves inhibition of K_V channels. Vasodilation to increased external K⁺ involves K_IR channels. Endothelium-derived hyperpolarizing factor activates K⁺ channels that are not yet clearly defined. Such K⁺ channel modulations, through their effects on membrane potential and contractile tone, make important contributions to the regulation of blood flow.     

BK<Subscript>Ca</Subscript> and K<Subscript>V</Subscript> channels limit conducted vasomotor responses in rat mesenteric terminal arterioles

Intracellular Ca²⁺ signals underlying conducted vasoconstriction to local application of a brief depolarizing KCl stimulus was investigated in rat mesenteric terminal arterioles (<40 μm). Using a computer model of an arteriole segment comprised of coupled endothelial cells (EC) and vascular smooth muscle cells (VSMC) simulations of both membrane potential and intracellular [Ca²⁺] were performed. The “characteristic” length constant, λ, was approximated using a modified cable equation in both experiments and simulations. We hypothesized that K⁺ conductance in the arteriolar wall limit the electrotonic spread of a local depolarization along arterioles by current dissipation across the VSMC plasma membrane. Thus, we anticipated an increased λ by inhibition of voltage-activated K⁺ channels. Application of the BK_Ca channel blocker iberiotoxin (100 nM) onto mesenteric arterioles in vitro and inhibition of BK_Ca channel current in silico increased λ by 34% and 32%, respectively. Similarly, inhibition of K_V channels in vitro (4-aminopyridine, 1 mM) or in silico increased λ by 41% and 21%, respectively. Immunofluorescence microscopy demonstrated expression of BK_Ca, Kv1.5, Kv2.1, but not Kv1.2, in VSMCs of rat mesenteric terminal arterioles. Our results demonstrate that inhibition of voltage-activated K⁺ channels enhance vascular-conducted responses to local depolarization in terminal arterioles by increasing the membrane resistance of VSMCs. These data contribute to our understanding of how differential expression patterns of voltage-activated K⁺ channels may influence conducted vasoconstriction in small arteriolar networks. This finding is potentially relevant to understanding the compromised microcirculatory blood flow in systemic vascular diseases such as diabetes mellitus and hypertension.     

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

Large-conductance Ca²⁺-activated K⁺ (BK_Ca) 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 BK_Ca channel activity in thoracic aorta smooth muscle cells (SMCs) in 20 sedentary (SED) and 40 training rats, submitted to a treadmill training protocol (20 m/min, 60 min/day, 12 weeks). Training rats were divided into two groups, exercising 3 days/week (EX1) and 5 days/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^?5 M NE was significantly decreased after training. In precontracted thoracic aorta with NE (10^?5 M), activation of the BK_Ca channels by NS1619 significantly decreased the tension. The sensitivity of tissue to NS619 (pD2) was significantly correlated with volume of training (SED < EX1 < EX2). 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 BK_Ca 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 BK_Ca channels in vascular SMCs, which contributes to improvement of the arterial function in thoracic aortas.     

Ghrelin signalling in guinea-pig femoral artery smooth muscle cells

Aim: Our aim was to study the new signalling pathway of ghrelin in the guinea‐pig femoral artery using the outward I_K as a sensor. Methods: Whole‐cell patch‐clamp experiments were performed on single smooth muscle cells, freshly isolated from the guinea‐pig femoral artery. The contractile force of isometric preparations of the same artery was measured using a wire‐myograph. Results: In a Ca²⁺‐ and nicardipine‐containing external solution, 1 mmol L^?1 tetraethylammonium reduced the net I_K by 49 ± 7%. This effect was similar and not additive to the effect of the specific BK_Ca channel inhibitor iberiotoxin. Ghrelin (10^?7 mol L^?1) quickly and significantly reduced the amplitudes of tetraethylammonium‐ and iberiotoxin‐sensitive currents through BK_Ca channels. The application of 5 × 10^?6 mol L^?1 desacyl ghrelin did not affect the amplitude of the control I_K but it successfully prevented the ghrelin‐induced I_K decrease. The effect of ghrelin on I_K was insensitive to selective inhibitors of cAMP‐dependent protein kinase, soluble guanylyl cyclase, cGMP‐dependent protein kinase or a calmodulin antagonist, but was effectively antagonized by blockers of BK_Ca channels, phosphatidylinositol‐phospholipase C, phosphatidylcholine‐phospholipase C, protein kinase C, SERCA, IP₃‐induced Ca²⁺ release and by pertussis toxin. The ghrelin‐induced increase in the force of contractions was blocked when iberiotoxin (10^?7 mol L^?1) was present in the bath solution. Conclusions: Ghrelin reduces I_K(Ca) in femoral artery myocytes by a mechanism that requires activation of Gα_i/o‐proteins, phosphatidylinositol phospholipase C, phosphatidylcholine phospholipase C, protein kinase C and IP₃‐induced Ca²⁺ release.