Caffeine induces periodic oscillations of Ca2+-activated K+ current in pulmonary arterial smooth muscle cells

The periodic oscillations of outward currents were studied in smooth muscle cells of the rabbit pulmonary artery. The combined stimuli of superfusion with 1 mM caffeine and depolarization of the membrane potential to 0 mV evoked periodic oscillations of outward currents with fairly uniform amplitudes and intervals. The oscillating outward currents induced by caffeine were dependent on intracellular Ca²⁺ concentration ([Ca²⁺]_i) and had a reversal potential near to the equilibrium potential for K⁺. So the oscillating outward currents are carried by K⁺ through Ca²⁺-dependent K⁺ channels (I _K(Ca)), and may reflect the oscillations of [Ca²⁺]_i. The oscillating outward currents were abolished, or their frequency reduced, by lowering external [Ca²⁺], Ca²⁺ channel blockers, or by 1 M ryanodine, indicating that: (1) there is a continuous influx of Ca²⁺ through the plasma membrane at a holding potential of 0 mV; (2) the periodic transient increases of [Ca²⁺]_i are ascribed to the rhythmic release of Ca²⁺ from ryanodinesensitive intracellular store by the mechanism of Ca²⁺-induced Ca²⁺ release (CICR). On the basis of the above results, we simulated the oscillation of [Ca²⁺]_i induced by caffeine, which is known to lower the threshold of CICR. The patterns of peak amplitude histograms of spontaneous transient outward currents (STOC) in the oscillating cells were different from those in non-oscillating cells. The amplitudes of STOC in the latter were more variable than those in the former. The oscillating outward currents were modulated by 1 M forskolin and 1 M sodium nitroprusside, but STOC were little affected. The above differences between STOC and oscillating outward currents suggest that the two currents are activated by the Ca²⁺ originating from different intracellular Ca²⁺ stores which are functionally heterogeneous.     

Neomycin inhibits K+-induced force and Ca2+ channel current in rat arterial smooth muscle

 The techniques of small vessel isometric myography and patch clamp were used to investigate the action of neomycin on K⁺-induced isometric force and voltage-gated Ca²⁺ channel currents in rat arterial smooth muscle. Neomycin and the dihydropyridine (DHP) Ca²⁺ channel antagonist (–)202–791 concentration-dependently and reversibly inhibited 40 mM K⁺-induced isometric force in rings of rat mesenteric and basilar arteries (IC₅₀ values of 70 μM and 1.2 nM, respectively, n = 10 and 4). Elevation of [Ca²⁺]_o by a factor of 2 significantly reduced the IC₅₀ values for inhibition of K⁺-induced force for both neomycin and (–)202–791 (192 μM and 3.7 nM, respectively, n = 6 and 4), but did not affect the Hill coefficient of the concentration/effect relationships. In patch-clamp experiments using freshly isolated basilar arterial myocytes, the voltage-gated inward current carried by Ba²⁺ was reversibly and concentration-dependently inhibited by neomycin (IC₅₀ 32 μM, n = 3). The concentration/effect curve for inhibition of the inward Ba²⁺ current by neomycin was significantly shifted to the right when [Ba²⁺]_o was raised from 1.8 mM to 10 mM (IC₅₀ 144 μM, n = 8). Our findings suggest that neomycin relaxes high-K⁺-induced force in rat isolated mesenteric and basilar arteries largely by inhibition of voltage-dependent and DHP-sensitive Ca²⁺ channels. Received: 1 August 1996 / Received after revision and accepted: 11 September 1996     

糖尿病胃轻瘫大鼠胃平滑肌细胞BK_(Ca)通道的变化

目的:探讨糖尿病胃轻瘫(DGP)的发病机制与胃平滑肌细胞大电导钙激活钾通道(BKCa)变化之间的关系。方法:将大鼠分为对照组和糖尿病胃轻瘫模型组。应用木瓜蛋白酶液急性酶分离大鼠胃平滑肌细胞,采用单通道膜片钳技术记录大鼠胃平滑肌细胞BKCa电流,免疫组织化学技术测定BKCa蛋白KCNMA和KCNMB1的表达。结果:大鼠胃平滑肌细胞BKCa电流的开放具有电压依赖性和胞内钙离子浓度依赖性,可被钾离子通道阻滞剂Ib TX阻断;模型组大鼠胃平滑肌细胞BKCa开放概率及开放幅度增加(P0.05),平均开放时间及平均关闭时间减少(P0.01);模型组大鼠胃平滑肌细胞KCNMB1蛋白表达增加(P0.01),KCNMA蛋白表达无明显变化。结论:DGP发病与胃平滑肌细胞BKCaβ1亚基蛋白表达上调及通道功能活动增强有关,β1亚基蛋白可能通过调节BKCa功能活动参与DGP的发生。     

Single K+ channels in membrane evaginations of smooth muscle cells

Attempts have been made to apply the patch-clamp technique to enzymatically dispersed smooth muscle cells of frog and toad stomach. The rate of successful gigaseal formation has been extremely low, but better results can be obtained when patches are taken from membrane evaginations which develop on single cells after mechanical agitation and incubation in Ca²⁺-containing solutions at 25° C. Also ball-shaped single cells formed by the confluence of membrane evaginations were found to be equally useful for patch-clamp studies. Giga-seal formation was obtained in more than 80% of all attempts. Electron micrographs indicate that the myofilaments in membrane evaginations an in ball-shaped cells are separated from the cell membrane. Channel activity in membrane patches of such myoballs or evaginations is similar to the channel activity as found in intact cells. Two types of K⁺ channels (100 and 200 pS) have been observed that can be blocked by tetraethylammonium. Channels with the conductance of 200 pS are activated by intracellular Ca²⁺. The formation of evaginations has also been observed in other cells and may help to apply the patch-clamp technique to cells contaminated with surface coats.     

Modulation of large conductance Ca2+-activated K+ channel by Gαh (transglutaminase II) in the vascular smooth muscle cell

 Among G-proteins, G_h is unique in structural differences in the GTP-binding domain and possessing transglutaminase activity. We have studied the role of G protein in modulation of large conductance Ca²⁺-activated K⁺ (Maxi-K⁺) channel by the inside-out mode of patch clamp in smooth muscle cells from superior mesenteric artery of the rabbit. When the non-hydrolyzable GTP analogue, GTPγS, was applied, the channel activity was increased about 2.5-fold. Addition of GDPβS resulted in reversal of the GTPγS effect. When the Gα_h7 antibody was applied, the GTPγS-stimulated channel activity was significantly inhibited to control level, suggesting that Gα_h is involved in activation of the Maxi-K⁺ channel in smooth muscle cells. Received: 23 September 1996 / Received after revision: 26 November 1996 / Accepted: 3 December 1996     

NADH and NAD modulates Ca2+-activated K+ channels in small pulmonary arterial smooth muscle cells of the rabbit

We have investigated the effect of NADH and NAD on the gating of large conductance Ca²⁺-activated K(K_Ca) channels in arterial smooth muscle cells isolated from small pulmonary artery(outer diameter <300μm) and ear artery, using the patch clamp technique. In the inside-out configuration, intracellularly applied 2 mM NADH inhibited the activity of K_Ca, channels in pulmonary arterial smooth muscle cells, while it had no significant effect on ear arterial smooth muscle cells. On the other hand, 2 mM NAD increased the opening of K_Ca, channels in pulmonary arterial smooth muscle cells. The effects of another intracellular redox couple, glutathione(GSH) and glutathione disulfide(GSSG) were also dependent on their redox potentials. GSH(5 mM) inhibited K_Ca. channels activity, while GSSG(5 mM) increased the activity of pulmonary arterial smooth muscle cells. It could be concluded that the modulation of K_Ca channels by intracellular redox state contributes, at least in part, to the hypoxic suppression of outward current in pulmonary arterial smooth muscle cells.     

Modulation of voltage-dependent K+ channel by redox potential in pulmonary and ear arterial smooth muscle cells of the rabbit

 It has been suggested that hypoxic pulmonary vasoconstriction (HPV) results from the depolarization that is induced by the suppression of K⁺ current in pulmonary arterial smooth muscle cells (PASMC). We tested the hypothesis that the effect of the cellular redox potential on voltage-sensitive K⁺ (Kv) current is involved in HPV as a primary sensing mechanism. Kv current in PASMC and ear arterial smooth muscle cells (EASMC) of the rabbit was recorded using the whole-cell patch-clamp technique, and the effect of redox agents [dithiothreitol, DTT and 2,2’-dithio-bis(5-nitropyridine), DTBNP] was tested. Kv current was decreased by DTT, but increased by DTBNP. DTT accelerated the inactivation kinetics, but did not affect steady-state activation and inactivation, whereas DTBNP accelerated activation kinetics. Kv current has a non-inactivating window in the range of from –40 mV to +10 mV. The resting membrane potential measured using the nystatin-perforated-patch method, however, lay between –50 mV and –30 mV and was not depolarized by 5 mM 4-aminopyridine. The membrane-impermeable oxidizing agent DTNB has no effect on Kv current, suggesting that redox modulation sites are intracellular sulphydryl groups. In EASMC, Kv current was decreased by DTT, but increased by DTBNP, indicating that the redox-potential-induced modulation of Kv current in EASMC and in PASMC is the same. It is therefore concluded that Kv current is modulated by the cellular redox potential, but that this modulation is not involved in HPV as a primary sensing mechanism. Received: 8 May 1997 / Received after revision: 20 June 1997 / Accepted: 23 June 1997     

Characterization of the ATP-inhibited K+ current in canine coronary smooth muscle cells

Intracellular adenosine triphosphate (ATP)-inhibited K⁺ currents (I _{K, ATP} ) in canine coronary artery smooth muscle cells were characterized in the wholecell configuration using the suction pipette method. Cells dialysed internally with solutions containing 5 mM ATP (ATP_i) showed little detectable whole-cell current at potentials more negative than –30 mV. However, cells dialysed with ATP_i-free solutions developed a time- and voltage-independent current which reached a maximum of 132±25 pA at –40 mV about 10 min following patch rupture. After run-up, the current showed little run-down. Concentration-dependent inhibition by ATP_i yielded an inhibition constant (K _i of 350 M and a Hill coefficient of 2.3. In ATP_i-free solutions, the large current at –40 mV was reduced by glibenclamide with aK _i of 20 nM and a Hill coefficient of 0.95. Conversely, in 1 mM ATP_i solutions, the small current at –40 mV was increased by P-1075 from 8±2 pA to 143±33 pA, with a dissociation constant (K _d) of 0.16 M and a Hill coefficient of 1.7. The effect of P-1075 was antagonized by glibenclamide. Maximal current density elicited by either ATP_i depletion or external application of the channel opener P-1075 was similar with slope conductances of 81±10 pS/pF and 76±13 pS/pF respectively in the potential range of –90 to –40 mV. External Ca²⁺ had no effect on this current. Finally, in 1 mM ATP_i, 20 and 50 M adenosine increased the current slope conductance by 36±15% and 73±10% respectively between –90 to –40 mV. TheI _{K, ATP} although very small in these cells, was extremely effective in causing membrane potential hyperpolarization.     

Effects of aging on Ca2+ signaling in murine mesenteric arterial smooth muscle cells

Pathophysiological changes in arterial smooth muscle structure and function occur with aging and there are a number of reports illustrating reductions in vascular responsiveness with aging. While much is known about arterial remodeling and functional adaptations with aging, very little is known about the biophysical adaptations in individual arterial myocytes. Cytosolic Ca2+ signaling, involving activation of L-type Ca2+ channels on the plasma membrane as well as InsP3 and ryanodine receptors on the sarcoplasmic reticulum, is integral to vascular tone and reactivity. Thus, we tested the hypothesis that aging results in reductions in the functional expression of L-type channels and temporal aspects of ryanodine receptor and InsP3 receptor Ca2+ signaling, in mesenteric arterial smooth muscle cells isolated from 6 and 30 months old C57Bl/6 mice. Comparisons of L-type current activity were made using dialyzed, whole-cell voltage-clamp techniques and Ba2+ as charge carrier. Ca2+ signaling was measured using fura-2 fluorescence microscopy techniques. Cell morphological changes were also investigated using electrophysiological and immunocytochemical approaches. The amplitudes of L-type Ca2+ currents were increased in older mice, but this was associated with membrane surface area increases of approximately 50%, due to increases in cell length not cell width. Consequently, L-type Ca2+ current densities were preserved with age, indicating functional channel expression was unchanged. In contrast, aging was associated with decrements in Ca2+ signaling in response to either ryanodine receptor stimulation by caffeine or InsP3 receptor activation with phenylephrine. These changes with aging may be related to the previously reported depression in myogenic reactivity.     

槲皮素抑制内皮素-1诱导的人脐动脉平滑肌细胞T型钙通道的表达

目的: 通过观察原代培养的人脐动脉平滑肌细胞在内皮素(ET-1)作用下对T型钙通道(TCC)的影响,进一步探讨槲皮素(Que)对心血管的保护作用。方法: 原代培养人脐动脉平滑肌细胞,经鉴定于2-3代用于实验。将细胞随机分成对照组、Que组、 模型组和实验组。对照组:不加入任何药物;Que组:加入Que 80 μmol/L培养24 h模型组:加入100 nmol/L ET-1培养24 h;实验组:加入Que培养1 h后,再加入100 nmol/L ET-1共同培养24 h,其中Que的浓度为20、40、80 μmol/L。采用RT-PCR和Western blotting检测TCC的主要亚基α_1G在mRNA和蛋白水平的表达。利用全细胞膜片钳技术,检测TCC电流(I_CaT)。结果: 模型组α_1G mRNA和蛋白的表达均强于对照组和实验组(P＜0.05),模型组I_CaT密度明显大于对照组和实验组(P＜0.01),而对照组和Que组的实验结果无明显差别(P＞0.05)。结论: ET-1诱导人血管平滑肌细胞中TCC的表达和I_CaT的增强,Que能抑制这种增强效应。这可能是Que发挥保护心血管功能的机制之一。     

Single anion-selective channel and its ion selectivity in the vascular smooth muscle cell

The properties of voltage-gated Cl channels of cultured smooth muscle cell prepared from embryonic rat aorta were studied. In the excised patch (inside-out configuration), we observed the activity of channels, opening and closing spontaneously, when the membrane potential was held at around 0 mV. The channels were active at a potential range between +10 and ?10 mV. A step change of the membrane potential from the active potential range in either a positive or a negative direction closed the channel to an apparently inactivated state. The time course of this inactivation process became faster as the amplitude of the step change was increased. Returning the membrane potential to 0 mV allowed the channel to recover from the inactivated state. The channel had at least two open conductance states. Ca ions at the cytoplasmic face were not required for the activation of the channel. Adenosine nucleotides at the same side of the membrane had no effect on channel activity. The channels were selective to anions rather than cations, and they had a large single channel conductance of 340.5±20.4 pS in symmetrical 150 mM TEA-Cl. The reversal potential of the channel was shifted by ?15.2±2.6 and 17.0±1.7 mV, when the Cl concentration at the intracellular side was changed to 75 mM or 300 mM, respectively. The permeability sequence of halides was I^?>Br^?>Cl^?>F^? (1.4∶1.3∶1.0∶0.7), whereas the conductance sequence was Cl^?>Br^?>F^?>I^? (1.00∶0.89∶0.86∶0.83). The internal dimension of the channel was estimated by measuring the permeability of various anions with different molecular cross section. We suggest that the smallest cross section of the channel pore is about 32Ų.     

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。     

丹参素对猪冠脉平滑肌细胞钙激活钾通道的作用

目的观察丹参素(DS-182)对原代培养猪冠脉平滑肌细胞钙激活钾通道(KCa)的作用,从单个钾通道水平揭示其扩冠机制。方法采用膜片钳单通道电流记录技术。结果①猪冠脉平滑肌细胞KCa的单通道电导值高,为(291.74±4.89)pS;对膜电位变化及细胞内钙离子浓度变化敏感,能被5~20 mmol/L膜内侧四乙基铵(TEA)所阻断。②在细胞贴附式膜片方式下,细胞外应用10~20μmol/L的DS-182对通道具明显的激活效应;而在内面向外式膜片方式下,细胞内应用5~30μmol/L的DS-182对通道均无明显作用。结论DS-182对通道的激活作用是非直接的,需要一系列的胞内过程。     

A newly identified Ca2+ dependent K+ channel in the smooth muscle membrane of single cells dispersed from the rabbit portal vein

We found a new type of Ca²⁺-dependent K⁺ channel in smooth muscle cell membranes of single cells of the rabbit portal vein. A slope conductance of the current was 180 pS when 142 mM K⁺ solution was exposed to both sides of the membrane (this channel was named the K_M channel, in comparison to the known K_L and K_S channels from the same membrane patch; Inoue et al. 1985). This K_M channel was less sensitive to the cytoplasmic Ca²⁺ concentration, [Ca²⁺]_i, but was sensitive to the extracellular Ca²⁺, [Ca²⁺]_o, e.g. in the outside-out membrane patch, lowering the [Ca²⁺]_o in the bath markedly reduced the open probability of this channel, and also in cell-attached configuration, lowering of the [Ca²⁺]_o using the internally perfused patch clamp electrode device reduced the opening of K_M channel. TEA⁺ (1–10 mM) reduced the amplitude of the elementary current through the K_M channel applied from each side of the membrane, but this agent inhibited the K_M channel to a greater extent when applied to the inner than to the outer surface of the membrane. Furthermore, this K_M channel had a weak voltage dependency, and the open probability of the channel remained much the same within a wide range of potential (from –60 mV to +60 mV). Whereas most Ca²⁺-dependent K⁺ channels are regulated mainly by [Ca²⁺]_i and possess a voltage dependency, these properties of the K_M channel differed from other Ca²⁺-dependent K⁺ channels. The elucidation of this K_M channel should facilitate explanations of the actions of external Ca²⁺ or TEA⁺ on the membrane potential, in the smooth muscles of the rabbit portal vein.     

Inhibitory effect of rapamycin on proliferation of human umbilical arterial smooth muscle cells

Abstract

Objective: Rapamycin has a protective cardiovascular effect and inhibits proliferation and migration of vascular smooth muscle cells. We investigated the effects of rapamycin on proliferation of cultured human umbilical arterial smooth muscle cells (HUASMCs) by determining interleukin-6 (IL-6) levels.

Materials and methods: Adherent third-generation primary-cultured HUASMCs were used in the study, and MTT assay was used to measure the effects of different rapamycin concentrations on cell proliferation at various time points (3–96?h). RT-PCR was used to measure IL-6 mRNA expression and ELISA was used to measure IL-6 protein expression.

Results: After three passages, HUASMCs displayed >90% confluence. Inhibition of cell proliferation by rapamycin was both time and dose dependent. When the action concentration of rapamycin was 100?ng·mL^–1, the inhibitory effect was strongest after 48?h (30.25?±?2.40)%, and the follow-up study was conducted after 48?h. When the action time of rapamycin was 48?h, the inhibitory effect of 150?ng·mL^–1 at the action concentration was the strongest, and the inhibitory rate was (42.88?±?3.84)%. There was no significant difference between the inhibitory effect and the action concentration of 100?ng·mL^–1 (p>.05). Moreover, low (2?ng·mL^–1), moderate (10?ng·mL^–1), and high (100?ng·mL^–1) rapamycin concentrations down-regulated both IL-6 mRNA and expression factor in a dose-dependent manner.

Discussion and conclusions: Rapamycin inhibits proliferation of HUASMCs in vitro and through down-regulation of IL-6 expression.     

Adrenomedullin and adrenotensin regulate collagen synthesis and proliferation in pulmonary arterial smooth muscle cells

To understand the pathophysiological mechanisms of pulmonary arterial smooth muscle cell (PASMC) proliferation and extracellular-matrix accumulation in the development of pulmonary hypertension and remodeling, this study determined the effects of different doses of adrenomedullin (ADM) and adrenotensin (ADT) on PASMC proliferation and collagen synthesis. The objective was to investigate whether extracellular signal-regulated kinase (ERK1/2) signaling was involved in ADM- and ADT-stimulated proliferation of PASMCs in 4-week-old male Wistar rats (body weight: 100-150 g, n=10). The proliferation of PASMCs was examined by 5-bromo-2-deoxyuridine incorporation. A cell growth curve was generated by the Cell Counting Kit-8 method. Expression of collagen I, collagen III, and phosphorylated ERK1/2 (p-ERK1/2) was evaluated by immunofluorescence. The effects of different concentrations of ADM and ADT on collagen I, collagen III, and p-ERK1/2 protein expression were determined by immunoblotting. We also investigated the effect of PD98059 inhibition on the expression of p-ERK1/2 protein by immunoblotting. ADM dose-dependently decreased cell proliferation, whereas ADT dose-dependently increased it; and ADM and ADT inhibited each other with respect to their effects on the proliferation of PASMCs. Consistent with these results, the expression of collagen I, collagen III, and p-ERK1/2 in rat PASMCs decreased after exposure to ADM but was upregulated after exposure to ADT. PD98059 significantly inhibited the downregulation by ADM and the upregulation by ADT of p-ERK1/2 expression. We conclude that ADM inhibited, and ADT stimulated, ERK1/2 signaling in rat PASMCs to regulate cell proliferation and collagen expression.     

Modulation of large conductance calcium-activated K+ channel by membrane-delimited protein kinase and phosphatase activities

Large conductance Ca²⁺-activated K⁺ channel was identified and studied in excised inside-out membrane patches of freshly dispersed smooth muscle cells from rabbit gastric antrum. The current-voltage relationship of the single channel was linear from -80 to +80 mV of pipette voltage in which single channel conductance was 249±17.8 pS (n=19) in symmetrical concentration of K⁺ (145mM) across the patch. Activity of the channel (NPo) depended not only on cytoplasmic calcium concentration but also on membrane potential. MgATP increased NPo in a dose-dependent manner and Mg²⁺ was prerequisite for the effect. Okadaic acid (l00nM), inhibitor of protein phosphatases, increased NPo further in the presence of MgATP. Therefore, it would be concluded that activity of the calcium-activated K⁺ channel in gastric smooth muscle cells was controlled by phosphorylation state of the channel protein and the state is further modulated by membrane-delimited protein kinase and protein phosphatase activities.     

Fluoxetine protects against big endothelin-1 induced anti-apoptosis by rescuing Kv1.5 channels in human pulmonary arterial smooth muscle cells

Purpose

Pulmonary Kv channels are thought to play a crucial role in the regulation of cell proliferation and apoptosis. Previous studies have shown that fluoxetine upregulated the expression of Kv1.5 and prevented pulmonary arterial hypertension in monocrotaline-induced or hypoxia-induced rats and mice. The current study was designed to test how fluoxetine regulates Kv1.5 channels, subsequently promoting apoptosis in human PASMCs cultured in vitro.

Materials and Methods

Human PASMCs were incubated with low-serum DMEM, ET-1, and fluoxetine with and without ET-1 separately for 72 h. Then the proliferation, apoptosis, and expression of TRPC1 and Kv1.5 were detected.

Results

In the ET-1 induced group, the upregulation of TRPC1 and down regulation of Kv1.5 enhanced proliferation and anti-apoptosis, which was reversed when treated with fluoxetine. The decreased expression of TRPC1 increased the expression of Kv1.5, subsequently inhibiting proliferation while promoting apoptosis.

Conclusion

The results from the present study suggested that fluoxetine protects against big endothelin-1 induced anti-apoptosis and rescues Kv1.5 channels in human pulmonary arterial smooth muscle cells, potentially by decreasing intracellular concentrations of Ca²⁺.