糖尿病大鼠输精管平滑肌收缩超反应性及钙通道特性(英文)

为了解糖尿病对输精管平滑肌功能的影响及其机理,我们比较了链脲菌素(streptozotocin)所致糖尿病大鼠及共同龄对照组大鼠输精管平滑肌对电场刺激,氯化钾,去氧肾上腺素的反应及钙通道的改变。电场刺激引起的收缩反应是单收缩之后继以连续性收缩。糖尿病组单收缩幅度较大,两组连续收缩几乎相同。1μmol/L Bay K8644使糖尿病鼠输精管产生单收缩,对照组无影响。氯化钾引起的收缩和钙内流在两组都增强,但在1 μmol/L Bay K8644存在时,糖尿病组比对照组增加明显。10μmol/L去氧肾上腺素引起的收缩可完全被0.1μmol/L硝苯啶阻断。100μmol/L新霉素在对照组可完全抑制去氧肾上腺素引起的收缩,但在糖尿病组只能部分抑制,并使单收缩增强。用钙通道拮抗剂配体[~3H]PN200-110所做的结合实验表明,对照或糖尿病组钙通道的亲和力和结合位点的数量都没有明显的不同。在输精管可溶性成分中,蛋白激酶C含量在糖尿病组是对照组的两倍。这些结果提示在没有神经病变及钙通道数量不变的情况下,氯化钾增强链脲菌素所致糖尿病大鼠输精管的收缩反应部分是由于钙通道开放的概率和蛋白激酶C活性增强所致。     

糖尿病大鼠输精管平滑肌收缩超反应性及钙通道特征

为对解糖尿病对输精管平滑肌功能的影响及其机理，我们比较了链脲菌素（streptozotocin)所致糖尿病大鼠及其同龄对照组大鼠输精管平滑肌对电场刺激，氯化钾，去氧肾上腺素的反应及钙通道的改变，电场刺激引起的收缩反应是单收缩之后继以连续性收缩，糖尿病组单收缩幅度较大，两组连续收缩几乎相同。1μmol/L Bay K8644使糖尿病鼠输精管产生单收缩，对照组无影响。氯化钾引起的收缩和钙内流在两组都强，但在1μmol/L Bay K8644存在时，糖尿病组比对照组增加明显。10μmol/L去氧肾上腺素引起的收缩可完全被0．1μmol/L硝苯啶阻断。100μmol/L新霉素在对照组可完全抑制去氧肾上腺素引起的收缩，但在糖尿病组只能部分抑制，并使单收缩增强，用钙通道拮抗剂配体[^3H]PN200-110所做的结合实验表明，对照或糖尿病组钙通道的亲和力和结合位的数量都滑有明显的不同，在输精管可溶性成分中，蛋白激酶C含量在糖尿病组是对粗的两倍。这些结果提示在没有神经病变及钙通道数量不变吓，氯化钾增强链脲菌素所致糖尿病大鼠输糖管的收缩反应部分是由于钙通道开放的概率和蛋白激酶C活性增强所致。     

突触前组胺H_1和H_3受体对豚鼠输精管交感神经冲动传递的影响(英文)

(R)-α-甲基组胺(α-MeHA)低浓度抑制,高浓度增强电场刺激诱发的离体输精管收缩。上述效应可分别被thioperamide和氯苯那敏拮抗,Pyridelethyl-amine(Pyr)能增强电场刺激诱发的输精管收缩,α-MeHA和Pyr对于直接电刺激或去甲肾上腺素(NE)诱发的输精管收缩均无影响,以上表明,豚鼠输精管交感神经末稍分布有组胺H_3和H_1两种受体,它们分别介导抑制和促进NE的释放。     

β-萘甲基6,7二甲氧基异喹啉抗实验性心律失常及对α_1和α_2受体的阻断作用

β-MBDI可明显对抗哇巴因、CaCl_2及氯仿所致的心律失常,但对乌头碱引起的心律失常无效,在剂量为0.1～30μmol/L的范围内,可剂量依赖地增加豚鼠左心房收缩力.并减慢右心房频率.在大鼠肛尾肌和输精管可分别使苯福林(Phe)、可乐定(CLN)的量效曲线平行右移,最大反应(E_(max))不变,其pA_2值分别为6.47(α_1)及5.3(α_2),说明它对肾上腺素α_1及α_2受体均有对抗作用.     

突触前组胺H1和H3受体对豚鼠输精管交感神经冲动传递的影响

（Ｒ）－α－甲基组胺低浓度抑制，高浓度增强电场刺激诱发的离体输精管收缩。上述效应可分别被ｔｈｉｏｐｅｒａｍｉｄｅ和氯苯那敏拮抗。Ｐｙｒｉｄｅｌｅｔｈｙｌａｍｉｎｅ（Ｐｙｒ）能增强电场刺激诱发的输精管收缩，α－ＭｅＨＡ和Ｐｙｒ对于直接电刺激或去甲肾上腺素诱发的输精管收缩均无影响。以上表明，豚鼠输精管交感神经末稍分布有组胺Ｈ３和Ｈ１两种受体，它们分别介导抑制和促进ＮＥ的释放。     

间硝苯啶和硝苯啶对离体大鼠心脏缺血再灌注的保护作用

用离体大鼠心脏缺血再灌注模型,观察间硝苯啶和硝苯啶对左心室顺应性及收缩性能的保护作用。缺血30min复灌10min,左心室顺应性和增长压显著降低,左心室僵硬度常数显著增加(P<0.01)。预先ip间硝苯啶(m-Nif)或硝苯啶(Nil)60μg/kg bid×2d,离体灌注时,灌流给予0.5μmol/L m-Nif或Nif,20min可防止缺血再灌注后左心室顺应性、增长压和僵硬度常数的改变。m-Nif和Nif在作用强度上无显著差异。     

粉防己碱对培养乳牛基底动脉平滑肌细胞内游离钙浓度的影响

目的：研究粉防己碱对培养乳牛基底动脉平滑肌细胞游离钙浓度（[Ca^2 ]i)的影响。方法：利用AR－CM－MIC阳离子测定系统,采用Fura 2-AM为指示剂,测量单个细胞内[Ca^2 ]i。结果：粉防己碱10－100μmol/L对培养乳牛基底动脉平滑肌细胞静息[Ca^2 ]i无明显影响。在细胞外钙为1．3mmol/L,粉防己碱可浓度依赖性地抑制KC1引起[Ca^2 ]i的升高。咖啡因10mmol/L可诱导一次[Ca^2 ]i瞬间快速升高,随后自发回复到静息水平,粉防己碱10和30μmol/L对咖啡因诱导的[Ca^2 ]i瞬间升高没有作用,但高浓度（100μmol/L）粉防己碱抑制了[Ca^2 ]i瞬间升高。在细胞外钙为1.3mmol/L,苯肾上腺素10μmol/L可引起双相[Ca^2 ]i变化,包括快速升高相和持续升高相。在细胞外钙为零,苯肾上腺素仅引起[Ca^2 ]i的快速升高相。粉防己碱可浓度依赖性地抑制苯肾上腺素引起[Ca^2 ]i快速升高相。结论：在培养乳牛基底动脉平滑肌细胞,粉防己碱可能通过影响电压依赖性和苯肾上腺素受体介导的钙通道而抑制钙内流。高浓度粉防己碱也可能影响肌浆网钙释放或钙摄取。     

肌浆网钙泵的抑制不参与过氧化氢诱导的大鼠主动脉收缩

目的:研究肌浆网钙泵抑制是否参与H_2O_2诱导的大鼠主动脉收缩反应。方法:离体主动脉环张力实验比较H_2O_2及钙泵特异性抑制剂环匹阿尼酸(CPA)缩血管效应及其信号机制的差异。结果:H_2O_2和CPA均收缩去内皮主动脉环,但H_2O_2触发快速短暂相位相收缩,而CPA诱导缓慢持续的张力相收缩。在无钙液中,仅CPA30μmol/L而非H_2O_230μmol/L预处理取消苯肾上腺素10μmol/L缩血管效应。Thap-sigargin 30μmol/L诱导最大收缩反应时,仅H_2O_2能使血管环进一步收缩。另外,P_2受体拮抗剂suramin、RB-2(各100μmol/L)以及多种酶抑制剂包括PLC、PKC、PLA_2、COX和蛋白质酪氨酸激酶均能抑制H_2O_2而非CPA诱导的缩血管效应,但2-APB50μmol/L对两者都有抑制作用。结论:肌浆网钙泵抑制不是H_2O_2收缩大鼠去内皮主动脉的机制。     

多沙唑嗪光学异构体对小鼠膀胱逼尿肌作用及作用机制研究

目的观察多沙唑嗪[(±)Dox]及其对映体[(-)Dox和(+)Dox]对小鼠离体膀胱逼尿肌的作用并分析其机制。方法采用小鼠离体膀胱条张力实验及电场刺激诱发小鼠离体膀胱条收缩实验。结果卡巴胆碱浓度依赖性诱发小鼠膀胱逼尿肌收缩,苯肾上腺素对小鼠膀胱逼尿肌无收缩作用。1μmol/L的(-)Dox、(+)Dox或(±)Dox对卡巴胆碱诱发的收缩反应均无显著影响(P>0.05),1μmol/L的Atr可完全阻断其收缩反应;(-)Dox、(+)Dox和(±)Dox对电场刺激诱发小鼠膀胱逼尿肌收缩反应无显著影响(P>0.05)。结论药物或电刺激诱发的小鼠膀胱逼尿肌收缩反应无去甲肾上腺素能成分的参与,多沙唑嗪及其对映体对其收缩反应无影响。     

河豚毒素对电刺激诱发的兔隐动脉双相血管收缩反应的作用

目的采用兔离体隐动脉环标本,建立了双相血管收缩反应模型,并分析TTX(1~100 nmol.L-1)对两种收缩成分的影响。方法兔离体隐动脉血管环张力记录法及电场刺激诱发血管收缩法。结果本实验条件下的电场刺激(电压15 V、波宽1 m s、刺激频率2~16 Hz,连续刺激时程32 s)可诱发兔离体隐动脉产生双相收缩反应,且具有频率(2~16Hz)依赖性。钠通道选择性阻滞剂TTX 3 nmol.L-1对第一相收缩反应无影响,但是明显抑制第二相收缩反应,抑制率达44%~67%;TTX的浓度增加至10 nmol.L-1时,其对4~16 Hz电刺激诱发的第一相反应的抑制率为40%~57%,而对第二相反应的抑制率达90%以上。TTX(0.1μmol.L-1)对NA(0.01~30μmol.L-1)的累积量效曲线无任何影响,但是完全抑制了电刺激诱发的动脉环双相收缩反应。胍乙啶(10μmol.L-1)完全抑制电刺激诱发的双相收缩反应,但是不抑制外源性NA的收缩反应。结论建立了电场刺激诱发兔离体隐动脉环双相收缩反应模型,该双相收缩与交感神经兴奋及其递质的释放有关。     

Ryanodine- and cyclopiazonic acid-sensitive components in human vas deferens contractions to noradrenaline

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Effect of the Ca(2+)-ATPase inhibitor, cyclopiazonic acid, on electromechanical coupling in the guinea-pig ureter.

1. We have investigated the effect of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase inhibitor, cyclopiazonic acid (CPA), on electromechanical coupling in the guinea-pig ureter. All experiments were performed in capsaicin-pretreated (10 microM for 15 min) ureters to prevent the release of sensory neuropeptides from afferent nerves. 2. In organ bath experiments, electrical field stimulation (EFS, 10 Hz for 1 s, 5 ms pulse width, 60 V) produced tetrodotoxin- (1 microM) resistant phasic contractions which were enhanced by Bay K 8644 (1 microM) and abolished by nifedipine (10-30 microM). 3. CPA (10 microM) enhanced the EFS-evoked contractions both in the absence and presence of Bay K 8644. The effect of CPA was concentration-dependent between 1 and 30 microM. The response to 10 microM CPA was biphasic: the maximal enhancement (58 +/- 3% increase) was observed within 10-20 min from CPA administration, followed by a decline to a new steady state (25 +/- 5% increase over baseline) at 50-60 min. The effect of CPA was reversed by washout. 4. Ryanodine (100 microM) produced a prompt enhancement of the EFS-evoked contractions of the guinea-pig ureter, which peaked at 42 +/- 3% increase over baseline; the co-administration of CPA (10 microM) and ryanodine (100 microM) produced a peak effect (60 +/- 8% enhancement) which was not different from that produced by CPA alone. With either ryanodine alone or ryanodine plus CPA, the enhancement of the EFS-induced contractions was biphasic, showing a time-course similar to that observed with CPA alone. Tetraethylammonium (10 mM) produced a significantly larger effect (93 +/- 13% increase over baseline) and its effect was sustained throughout the 60 min observation period. 5. In the presence of Bay K 8644, superfusion for 30 min with a low Na+ medium (60% of extracellular Na+ replaced by Li+ or choline) reduced the amplitude of EFS-evoked contractions by 20-35%. In both Li(+)- and choline-substituted media, spontaneous activity developed during superfusion with low Na+ Krebs solution which was suppressed by 10 microM nifedipine. CPA (10 microM) produced a marked enhancement of the EFS-evoked contractions in low-Na+ medium (both Li(+)- and choline-substituted) and this effect was sustained throughout the 60 min observation period.(ABSTRACT TRUNCATED AT 400 WORDS)     

大鼠血管中α_1肾上腺素受体的两种亚型

α_1肾上腺素受体(α_1受体)激动引起的大鼠离体血管收缩,在主动脉可为不可逆性α_1受体拮抗剂CEC大部分阻断,而不受钙离子拮抗剂硝苯吡啶的影响;在肾动脉不受CEC阻断,却可为硝苯吡啶大部分阻断;在肠系膜动脉与门静脉则介于两者之间。竞争性α_1受体拮抗剂WB4101的pA_2值,肾动脉>肠系膜动脉>主动脉。根据已知α_1受体两种亚型的药理特征,上述结果提示大鼠血管中的α_1受体存在两种亚型,在主动脉内以α_(1b)亚型为主,在肾动脉内以α_(1a)亚型为主,在肠系膜动脉与门静脉内两种亚型的含量较为均衡。     

Different actions in the rat prostatic and epididymal vas deferens of cyclopiazonic acid or ryanodine on noradrenaline-induced contractions

The effects of ryanodine, cyclopiazonic acid (CPA), and nifedipine on noradrenaline (NA)-induced contractions were investigated to characterize the role of the sarcoplasmic reticulum (SR) in the epididymal and prostatic parts of the rat vas deferens. In the epididymal part, NA (0.1, 1, and 100 microM) evoked marked rhythmic contractions superimposed on a tonic response. NA (100 microM) evoked biphasic tonic contractions consisting of a fast (initial) component and delayed secondary components. Nifedipine (1 microM) suppressed the rhythmic activity and the contractions to low NA concentrations and markedly reduced the components of the response to NA (100 microM). Contractions of the epididymal part to NA (0.1, 1, and 100 microM) were not blocked by ryanodine (1-30 microM) or CPA (1-30 microM). The secondary component in the response to NA (100 microM) was enhanced by CPA (> or =10 microM). Thus in the epididymal part, NA stimulates contraction predominantly by mobilizing extracellular calcium. However, a residual nifedipine-insensitive contraction to NA (100 microM) was observed and was not blocked by ryanodine (30 microM) or CPA (30 microM). In the prostatic part, NA evoked mainly tonic contractions. The response to NA (100 microM) consisted of three distinct components. Nifedipine (1 microM) reduced the contractions to low concentrations of NA (0.1 and 1 microM) and all three components of the response to NA (100 microM). Contractions of the prostatic part to low concentrations of NA (0.1 and 1 microM) were not blocked by CPA (30 microM) or ryanodine (30 microM). The components of the response to NA (100 microM) were affected differently by the drugs. Ryanodine (17-30 microM) or CPA (1-30 microM) suppressed the initial component and reduced the second component. The third component was largely unaffected by CPA but reduced by ryanodine. In the additional presence of nifedipine (1 microM), the residual components of NA (100 microM) response were markedly reduced and the contractions to low concentrations of the agonist virtually abolished. These results suggest that NA contracts the prostatic part by mobilizing both extra- and intracellular calcium. These results show that NA-induced contractions of the epididymal and prostatic parts of the rat vas deferens differ in sensitivity to ryanodine or CPA. The results suggest that, during stimulation of the epididymal part, the SR functions mainly to buffer calcium entering through nifedipine-sensitive voltage-gated calcium channels. In contrast, in the prostatic part, the SR serves mainly as a source of calcium and contributes more to contractions evoked by higher concentrations of the agonist.     

Extracellular and intracellular calcium sources mediating contractile responses of smooth muscle in bovine ovarian follicle and ovarian artery

The relative importance of extracellular and intracellular calcium sources mediating smooth muscle contraction in ovarian follicle and ovarian artery was assessed in experiments on the influence of nifedipine, D-600, amrinone, diethylstilbestrol (DES), lanthanum and/or calcium removal on contractions induced by K+ depolarization, by noradrenaline, histamine and acetylcholine. The K+-induced response was biphasic in the ovarian artery but not in the ovarian follicle. The K+-induced contraction in both preparations was greatly inhibited by nifedipine (1 microM), D-600 (10 microM) and lanthanum (2 mM). Although both phases of the responses in the ovarian artery appeared to be completely dependent on extracellular calcium, phase I was significantly more sensitive to nifedipine than phase II. Incubation in calcium-free medium for 15 min almost abolished the K+-induced contraction. Noradrenaline- and histamine-induced contractions of ovarian follicle were essentially unaffected by nifedipine (1 microM) and D-600 (10 microM) whereas the noradrenaline-induced contraction in ovarian artery was inhibited significantly by D-600 (1 and 10 microM) but not nifedipine (1 microM). In calcium-free medium containing EGTA (1 mM) the responses of ovarian follicle to noradrenaline and histamine were reduced by 26 and 22% respectively. When preparations were stimulated with noradrenaline more than one in calcium-free medium, the contraction decreased progressively compared to time-matched controls. The response was 34% of the control after 50 min in calcium-free medium containing EGTA. In the ovarian artery the response obtained (6% of control) was significantly smaller (P less than 0.05) than that in the follicle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of calcium and alpha-adrenoceptors in contractile response of chick expansor secundariorum muscle to field stimulation

1. The effects of some alpha-adrenergic agonists and antagonists on electrically-evoked contractions and tension of chick expansor secundariorum muscle (ESM), and dependence of these events on extracellular calcium was investigated.2. Both train and continuous electrical stimulation can produce regular contractions in preparations obtained from 40–60 day old chicks.3. Clonidine had a biphasic action on the contractions produced by train electrical stimulation. In concentrations ranging from 10^-8 to 3 × 10^-7 M, clonidine decreased the contraction amplitude, but in higher concentrations, it caused an increase in both the muscle tension and the contraction amplitude. These effects were reversed by application of yohimbine although yohimbine by itself had no effect on the contractions.4. Introduction of calcium free isotonic high potassium medium decreased muscle tone which was followed by further dose-dependent increase in tension, along with the addition of cumulative doses of CaCl₂ (ED₅₀ = 2.8 × 10^-3 M).5. Nifedipine reduced the amplitude of ESM contractions produced by continuous electrical stimulation in a dose dependent manner (IC₅₀ = 6.7 × 10^-7 M).6. Methoxamine induced a completely dose dependent increase in muscle tension which was dependent on extracellular calcium and was inhibited by nifedipine. In the presence of 10^-8 M nifedipine, ED₅₀ of methoxamine stimulatory effect increased from the control value of 2.2 × 10^-7 to 8.4 × 10^-7 M.7. Although BAY-K8644, a calcium channel activator, had no effect on the contraction amplitude produced by continuous electrical stimulation, the muscle tension was increased by this drug in a dose dependent manner (ED₅₀ = 2.2 × 10^-8 M).     

Guanylate cyclase regulates ileal longitudinal muscle contractions induced by neurogenic nitrergic activity in the rat

1. Nitrergic neurons regulate gastrointestinal (GI) activity and their dysfunction has been associated with various GI diseases. Nitric oxide (NO) typically relaxes GI smooth muscle, but nitrergic contractions also occur. Although guanylate cyclase is well established as mediating nitrergic GI relaxation, its role in contraction remains uncertain. 2. We used electrical field stimulation (EFS; 0.3 msec pulses, three trains of 1.2 s width, 2 Hz, at 30 s intervals) to evoke biphasic contraction–relaxation responses in rat ileum strips (longitudinal muscle–myenteric plexus preparations), mediated by the endogenous nitrergic transmitter, under non‐adrenergic, non‐cholinergic (NANC) conditions (1 μmol/L atropine and 4 μmol/L guanethidine). 3. All EFS responses were abolished by tetrodotoxin (1 μmol/L). Inhibition of NO synthase with N^ω‐nitro‐l ‐arginine‐methyl‐ester (l ‐NAME; 100 and 300 μmol/L) prevented both EFS‐evoked contractions and relaxations. l ‐Arginine (3 mmol/L) reversed l ‐NAME inhibition, primarily restoring contractions and suggesting that these require lower nitrergic transmitter levels than relaxations. 4. Pretreatment of preparations with subrelaxant concentrations of sodium nitroprusside (1 μmol/L) selectively desensitized EFS‐evoked contractions without affecting relaxations, suggesting different downstream mechanisms. Nevertheless, the selective guanylate cyclase inhibitor 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (3 and 10 μmol/L) inhibited both nitrergic contractions and relaxations, indicating that guanylate cyclase activation is required for both responses. 5. The results of the present study support the hypothesis that the endogenous nitrergic transmitter differentially regulates guanylate cyclase, leading to either contractions or relaxations depending on its concentrations, thus providing additional insight into the regulation of ileum contractility by nitrergic activity.     

Effect of Bay K 8644 and ryanodine on the refractory period,action potential and mechanical response of the guinea-pig ureter to electrical stimulation

We have investigated the effect of the dihydropyridine calcium channel agonist, Bay K 8644, and of the plant alkaloid blocker of calcium-induced calcium release (CICR) from the sarcoplasmic reticulum, ryanodine, on the refractory period, action potential and mechanical response of the guinea-pig isolated ureter to electrical stimulation. All experiments were performed in ureters pre-exposed to 10 M capsaicin to eliminate the inhibitory influence exerted by local release of sensory neuropeptides on ureteral excitability and contraction. In organ bath experiments, electrical field stimulation with parameters which produce direct excitation of ureteral smooth muscle (train of pulses at 10 Hz, 5 ms pulse width, 60 V for 1 s) produced tetrodotoxin- (1 M) resistant phasic contractions. The response to EFS was abolished by nifedipine (1 nM-3 M) and was enhanced by Bay K 8644 (1 nM-3 M). In the presence of Bay K 8644 (1 M), nifedipine (30 M) abolished the evoked contractions. Ryanodine (10–100 M) had no significant effect on the amplitude of evoked contraction. The response of the guinea-pig ureter to direct electrical stimulation of smooth muscle is characterized by a refractory period: at least 40 s interstimulus interval was required to produce a second response in all preparations tested. Bay K 8644 (1 M) markedly reduced the refractory period of the ureter and a similar effect was observed with ryanodine (100 M). To further analyze the effect of Bay K 8644 and ryanodine on the refractory period, the response of the ureter was investigated over a 10 s period of stimulation (other parameters as above). In control ureters, continuous stimulation for 10 s produced only one phasic contraction just after the beginning of the train of stimuli. In the presence of Bay K 8644 or ryanodine, more than one phasic contraction developed during a 10 s stimulation, i.e. the refractory period became shorter than the train duration. When both Bay K 8644 and ryanodine were tested on the same preparations, an additive excitatory effect was observed on the mechanical response to electrical stimulation. A slight elevation of KCI concentration (5–10 mM) reduced the refractory period of the ureter as observed with ryanodine or Bay K 8644. Application of KCI (80 mM) produced a biphasic contractile response of the ureter: a series of phasic contractions occurred first, which were then replaced by a slowly developing tonic response. Bay K 8644 (1 M) enhanced both components of the response to KCI. Ryanodine (10 and 100 M) markedly prolonged the duration of phasic contractions evoked by KCI and, at 100 M, slightly (about 25%) reduced the amplitude of tonic contraction.In sucrose gap experiments, electrical stimulation (single pulse, 40–130 V, 1–3 ms pulse duration) evoked an action potential and accompanying phasic contraction which were abolished by 1 M, nifedipine. Bay K 8644 (1 M) produced a marked prolongation of action potential duration, increased the number of spikes and enhanced contraction amplitude and duration. Ryanodine (100 M) depolarized the membrane, reduced the delay between stimulus application and onset of the action potential, shortened the action potential at 50% of repolarization and increased afterhyperpolarization, without producing marked effects on the accompanying mechanical response. KCI (5 mM) likewise produced a slight membrane depolarization and decreased latency between stimulus application and onset of the action potential but did not affect action potential duration. The combined administration of ryanodine and Bay K 8644 produced additive effects on action potential and contractions: furthermore, the contractile phase of the overall contraction-relaxation cycle was significantly prolonged by the combined administration of the two agents, an effect not observed with either drug alone. In the presence of both Bay K 8644 and ryanodine, multiple action potentials and contractions were observed during a train of pulses delivered at a frequency of 1 Hz for 12 s: when a second action potential was triggered before relaxation of the preceding contraction, a summation of the contractile response was observed. These findings demonstrate that availability of voltage-dependent L-type calcium channels is a major mechanism in determining the refractory period of the guinea-pig ureter and, consequently, can be considered as a limiting step in regulating the maximal frequency of ureteral peristalsis. Furthermore, a ryanodine-sensitive mechanism regulates the excitability and contraction-relaxation cycle of ureteral smooth muscle. The increased electrical excitability of the ureter observed in the presence of ryanodine may involve blockade of transient outward currents triggered by spontaneous calcium release from the store and consequent membrane depolarization.     

Doxorubicin-induced vasomotion and [Ca^2＋]i elevation n vascular smooth muscle cells from C57BL/6 mice

Aim:

To explore the action of doxorubicin on vascular smooth muscle cells.

Methods:

Isometric tension of denuded or intact thoracic aortic vessels was recorded and [Ca²⁺]_i in isolated aortic smooth muscle cells was measured by using Fluo-3.

Results:

Doxorubicin induced phasic and tonic contractions in denuded vessels and increased levels of [Ca²⁺]_i in single muscle cells. Treatment with 10 μmol/L ryanodine had no effect on basal tension, but it did abolish doxorubicin-induced phasic contraction. Treatment with 10 mmol/L caffeine induced a transient phasic contraction only, and the effect was not significantly altered by ryanodine, the omission of extracellular Ca²⁺ or both. Phenylephrine induced rhythmic contraction (RC) in intact vessels. Treatment with 100 μmol/L doxorubicin enhanced RC amplitude, but 1 mmol/L doxorubicin abolished RC, with an increase in maximal tension. Caffeine at 100 μmol/L increased the frequency of the RC only. In the presence of 100 μmol/L caffeine, however, 100 μmol/L doxorubicin abolished the RC and decreased its maximal tension. Treatment with 10 μmol/L ryanodine abolished the RC, with an increase in the maximal tension. In Ca²⁺-free solution, doxorubicin induced a transient [Ca²⁺]_i increase that could be abolished by ryanodine pretreatment in single muscle cells. The doxorubicin-induced increase in [Ca²⁺]_i was suppressed by nifedipine and potentiated by ryanodine and charybdotoxin.

Conclusion:

Doxorubicin not only releases Ca²⁺ from the sarcoplasmic reticulum but also promotes the entry of extracellular Ca²⁺ into vascular smooth muscle cells.     

Differential roles of ryanodine- and thapsigargin-sensitive intracellular CA2+ stores in excitation-contraction coupling in smooth muscle of guinea-pig taenia caeci

1. To explore roles of intracellular Ca(2+) stores in excitation-contraction coupling in smooth muscle, we examined the effects of ryanodine, a fixer of ryanodine receptor-Ca(2+) channels to an open state, and thapsigargin, a selective inhibitor of the Ca(2+) pump in the intracellular stores, on smooth muscle contraction in the presence and absence of extracellular Ca(2+) in guinea-pig taenia caeci. 2. In Ca(2+) -free solution, contractions induced by 0.1 mmol/L carbachol and 0.1 mmol/L histamine were reduced to approximately 65% of control by either 1 micro mol/L thapsigargin or 10 micro mol/L ryanodine. In contrast, caffeine-induced contraction was reduced to approximately 40% of control by ryanodine, but was not affected by thapsigargin. 3. In the presence of extracellular Ca(2+), thapsigargin slowly induced a large and sustained contraction. In contrast, ryanodine did not induce an apparent contraction, but increased the sensitivity of contractile responses to receptor agonists (carbachol, AHR-602 and histamine) or depolarizing high K(+) with no changes in the maximal contraction. 4. These results suggest that there are pharmacological and physiological differences between ryanodine- and thapsigargin-sensitive intracellular Ca(2+) stores in excitation-contraction coupling in smooth muscle, which may be responsible for their differential effects on the Ca(2+) -influx pathway.