Purinergic modulation of pacemaker Ca2+ activity in interstitial cells of Cajal

Purinoceptors are widely distributed throughout the body, and are thought to have important contributions to numerous functions. In this study, we characterised the contribution of purinoceptors to the mechanisms underlying spontaneous rhythmicity of the gastro-intestinal tracts. Using cell cluster preparations (100-200 microm diameter) obtained from murine ileum, we measured spontaneous intracellular Ca2+([Ca2+]i) oscillations in the presence of nifedipine, as an index of pacemaker [Ca2+]i activity in interstitial cells of Cajal (ICCs, c-Kit-immunopositive cells), the pacemaker cells for gastrointestinal motility. This small preparation also contained smooth muscle and enteric neurones. Using various purinoceptor agonists and an antagonist, we characterised both TTX-sensitive and insensitive modulations of pacemaker [Ca2+]i activity in ICCs. Continuous application of either ATP, ATPgammaS, suramin or alpha,beta-methylene ATP (alpha,beta-meATP) suppressed pacemaker [Ca2+]i activity. The inhibitory effect of alpha,beta-meATP was completely abolished by a prior application of TTX. On the other hand, even in the presence of TTX, continuous application of 2-methylthio ATP (2-MeSATP) at concentrations greater than 30 microM caused a prompt rise followed by a slow decline of the baseline [Ca2+]i, and pacemaker [Ca2+]i oscillations were gradually suppressed during the decline. Neither UTP nor alpha,beta-meATP at high concentrations (30-100 microM) produced a similar [Ca2+]i response. These results suggest that the TTX-resistant, direct purinergic modulation of pacemaker [Ca2+]i activity in ICCs is mediated via P2X purinoceptors distinct from those involved in TTX-sensitive modulation. The slow decline may be attributed to desensitisation of these purinoceptors. The possible involvement of other purinoceptors is also discussed.     

先天性肠闭锁Cajal间质细胞和突触素的研究

目的　探讨Cajal间质细胞(ICCs)和突触素与肠闭锁手术、术后肠动力障碍的关系。方法　采用Envision法免疫组织化学技术,对 30 例先天性肠闭锁(IA)盲端近端和远端肠标本及 4例正常对照标本,分别观察 ICCs和突触的形成情况。结果　在 IA组,ICCs和突触素在盲端近、远端的分布与正常对照组相比显著减少,ICCs网络被破坏。近端改变范围在8 cm左右,远端改变局限在1~2 cm,且随着远离闭锁盲端,上述指标有增加趋势。在对照组,ICCs大量分布于肠肌丛,并相互联接形成网络,肌间神经丛可见大量突触素表达。结论　先天性肠闭锁盲端近端和远端肠管有ICCs分布和突触形成的异常,手术中要尽量切除病变肠管,以免造成术后肠功能障碍。     

厚朴汁炙远志炮制品对胃问质细胞活力影响的探讨

目的：探索研究不同剂量厚朴汁炙远志炮制品对胃间质细胞活力的影响。方法：将实验分成空白组、远志组、厚朴组、厚朴汁炙远志高、中、低剂量组、远志配厚朴1：2组七个不同剂量组对培养的胃间质细胞进行干预,24h后采用四唑盐比色实验（MTT法）,考察厚朴炮制远志的水煎液及其含药血清对胃间质细胞活力的影响。结果：厚朴汁炙远志炮制品水煎液对胃间质细胞活力的影响结果显示,与单味生远志20g·kg^-1组比较,空白组、单味厚朴10g·kg^-1组、炮制高剂量30g·kg^-1组、远志配厚朴1：2（30g·kg^-1）组的胃间质细胞OD值均显著增高（F=2．750,P=0．024）;厚朴汁炙远志炮制品含药血清对胃间质细胞活力的影响结果显示,炮制高剂量30g·kg^-1组、远志配厚朴1：2（30g·kg^-1）组的含药血清的胃间质细胞OD值均显著高于空白组（F=10．22,P=0．000）;且单味厚朴10g·kg^-1。组、炮制高剂量30g·kg^-1。组、远志配厚朴1：2组（30g·kg^-1）的OD值均显著高于单味远志组（F=10．22,P〈0．05）。结论：远志有抑制胃动力起搏细胞活性趋势,单味厚朴组、厚朴汁炙远志炮制品组、远志配厚朴1：2组均能极显著促进胃间质细胞活力,从而促进胃动力,故推测厚朴能通过促进胃问质细胞的活力,在配伍和炮制过程中降低远志对胃间质细胞造成的伤害,而达到缓解胃肠动力障碍的目的。     

通腑化瘀汤对术后肠梗阻大鼠肠组织COX-2及Cajal间质细胞表达的影响

目的建立术后肠梗阻大鼠模型,观察通腑化瘀汤对术后肠梗阻大鼠肠组织环氧化酶-2(Cyclooxygenase-2,COX-2)及Cajal间质细胞(Interstitial cells of Cajal,ICC)表达的影响,评估肠粘膜损伤程度,为临床更好地防治术后肠梗阻提供有效的治疗方剂和理论依据。方法取健康雄性SD大鼠45只,随机分为通腑化瘀汤组(药物组)、生理盐水对照组(对照组)、空白组,药物组和对照组给予开腹手术建立术后肠梗阻模型,手术后6、16 h时间点分别给予通腑化瘀汤药液和生理盐水各0.8 m L灌胃,空白组不给予手术处理。处死前取大鼠小肠远端距盲肠约5 cm的肠组织,采用HE染色显微镜下观察肠粘膜损伤情况;免疫组织化学方法检测c-kit蛋白(ICC特异性标志物)和COX-2蛋白的平均光密度值。结果对照组与空白组相比,COX-2表达显著提高(P<0.05),c-kit表达显著降低(P<0.05),肠黏膜损伤程度较重;药物组与对照组相比,COX-2表达显著降低(P<0.05),c-kit表达显著提高(P<0.05),损伤的肠粘膜得到一定程度修复。结论通腑化瘀汤能够减少术后肠梗阻小肠组织COX-2的表达,改善ICC形态并提高ICC数量,抑制炎症反应,对受损伤的肠粘膜起到保护作用。     

心房肽Ⅲ对哺乳动物心肌电及机械活动的影响

本文报告APⅢ对豚鼠心乳头状肌动作电位、收缩力及犬心浦氏纤维Isi的作用。APⅢ于0.1～100nM浓度依赖性地增强豚鼠心乳头状肌的等长收缩张力及延长其APD_(90)和ERP。10nM时作用最明显,F_c提高27.6％,APD_(90)和ERP分别延长23和25ms。对动作电位的其它参数没有明显影响。其正性肌力、延长APD_(90)和ERP等作用,于给药后3 min开始,10 min达最大,维持时间可达30 min。APⅢ 30nM对使犬心浦氏纤维Isi增加18.6％。结果表则,APⅢ对哺乳动物心肌具有直接作用,提示分泌心房肽的器官-心脏也为该物质的靶器官之一。     

甲基莲心碱对豚鼠心肌电—机械活动的影响

甲基莲心碱(Nef)0.1mM使豚鼠右心室乳头状肌的收缩力降低68. 3％,使动作电位APA和Vmax分别从112±5mV,240±37V/s降低到97±9 mV和86±25V/s;APD_(50),APD_(90)和ERP分别从173±23ms,205±17ms和201±16ms延长到201±26ms,239±28ms和249±23ms。Nef 1-200μM浓度依赖性地延长APD_(50),APD_(90)和ERP,降低Vmax和收缩力。30μM Nef能明显对抗10μM乙酰胆碱缩短豚鼠左心房APD的作用。结果提示,Nef对心肌Na~+,K~+,Ca~(2+)的跨膜转运均有抑制作用。     

The properties of spontaneous transient inward currents of interstitial cells in rabbit portal vein

The present study was designed to investigate the properties of spontaneous transient inward currents generated by interstitial cells (ICs) in the rabbit portal vein. Single ICs were freshly isolated from smooth muscle of the rabbit portal vein enzymetically. Using whole-cell patch clamp techniques, the spontaneous transient inward currents (STICs) were recorded at −60 mV of holding potential in freshly dispersed ICs. Both gadolinium, a non-selective cation channel inhibitor, and niflumic acid, a calcium-activated chloride channel blocker, abolished the inward currents. Replacement of external Na⁺ with N-methyl-d-glucamine (NMDG⁺) also blocked the inward currents. The inward currents were abolished by caffeine, carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP), thapsigargin and ryanodine, but were partly inhibited by 2-aminoethoxydiphenyl borate (2-APB). W-7, a calmodulin inhibitor, increased the amplitude of the inward currents. These results suggest that non-selective cation channels are involved in the generation of the spontaneous transient inward currents recorded from ICs. The currents are regulated by intracellular calcium and calmodulin. But in the present study, the involvement of the calcium-activated chloride channels in the generation of the currents cannot be excluded.     

Inhibition of pacemaker currents by nitric oxide via activation of ATP-sensitive K+ channels in cultured interstitial cells of Cajal from the mouse small intestine

We investigated the role of nitric oxide (NO) in pacemaker activity and signal mechanisms in cultured interstitial cells of Cajal (ICC) of the mouse small intestine using whole cell patch-clamp techniques at 30°C. ICC generated pacemaker potential in the current clamp mode and pacemaker currents at a holding potential of –70 mV. (±)-S-nitroso-N-acetylpenicillamine (SNAP; a NO donor) produced membrane hyperpolarization and inhibited the amplitude and frequency of the pacemaker currents, and increased resting currents in the outward direction. These effects were blocked by the use of glibenclamide (an ATP-sensitive K⁺ channel blocker), but not by the use of 5-hydroxydecanoic acid (a mitochondrial ATP-sensitive K⁺ channel blocker). Pretreatment with ODQ (a guanylate cyclase inhibitor) almost blocked the NO-induced effects. The use of cell-permeable 8-bromo-cyclic GMP also mimicked the action of SNAP. However, the use of KT-5823 (a protein kinase G inhibitor) did not block the NO-induced effects. Spontaneous [Ca²⁺]_i oscillations in ICC were inhibited by the treatment of SNAP, as seen in recordings of intracellular Ca²⁺ ([Ca²⁺]_i). These results suggest that NO inhibits pacemaker activity by the activation of ATP-sensitive K⁺ channels via a cyclic GMP dependent mechanism in ICC, and the activation of ATP-sensitive K⁺ channels mediates the inhibition of spontaneous [Ca²⁺]_i oscillations.     

Substance P induces inward current and regulates pacemaker currents through tachykinin NK1 receptor in cultured interstitial cells of Cajal of murine small intestine

We investigated whether substance P modulates pacemaker currents generated in cultured interstitial cells of Cajal of murine small intestine using whole cell patch-clamp techniques at 30 degrees C. Interstitial cells of Cajal generated spontaneous inward currents (pacemaker currents) at a holding potential of -70 mV. Tetrodotoxin, nifedipine, tetraethylammonium, 4-aminopyridine, or glibenclamide did not change the frequency and amplitude of pacemaker currents. However, divalent cations (Ni2+, Mn2+, Cd2+, and Co2+), nonselective cationic channel blockers (gadolinium and flufenamic acid), and a reduction of external Na+ from normal to 1 mM inhibited pacemaker currents indicating that nonselective cation channels are involved in their generation. Substance P depolarized the membrane potential in current clamp mode and produced tonic inward pacemaker currents with reduced frequency and amplitude in voltage clamp mode. [D-Arg1, D-Trp7,9, Leu11] substance P, a tachykinin NK1 receptor antagonist, blocked these substance P-induced responses. Furthermore, [Sar9, Met(O2)11] substance P, a specific tachykinin NK1 receptor agonist, depolarized the membrane and tonic inward currents mimicked those of substance P. Substance P continued to produce tonic inward currents in external Ca2+-free solution or in the presence of chelerythrine, a protein kinase C inhibitor. However, substance P-induced tonic inward currents were blocked by thapsigargin, a Ca2+-ATPase inhibitor in the endoplasmic reticulum or by an external 1 mM Na+ solution. Our results demonstrate that substance P may modulate intestinal motility by acting on the interstitial cells of Cajal by activating nonselective cation channels via the release of intracellular Ca2+ induced by tachykinin NK1 receptor stimulation.     

便秘型肠易激综合征大鼠肠道Cajal间质细胞的免疫组织化学研究

目的通过研究便秘型肠易激综合征(C-IBS)大鼠结肠肌层的Cajal间质细胞(ICC)c-kit表达,了解其在肠道内分布、数量等有无变化,以便探讨C-IBS可能的发病机制。方法采用对照组(n=10)和C-IBS组(n=10)对比研究,用c-kit抗体对结肠平滑肌标本进行SABC免疫组织化学染色,彩色病理图像软件分析染色阳性细胞的数量及强度。结果C-IBS大鼠结肠平滑肌c-kit阳性细胞数量减少,表达减弱(P<0.05)。结论ICC减少可能是C-IBS的发病机制之一。     

氯化汞对豚鼠心室肌电机械活动的影响

目的：观察氯化汞（ＨｇＣｌ２）对离体豚鼠乳头状肌的电生理作用。方法：采用心肌细胞内固定微电极技术。结果：ＨｇＣｌ２１～５０μｍｏｌ·Ｌ－１对豚鼠乳头状肌动作电位和收缩力的影响，具有剂量依赖性。ＨｇＣｌ２５μｍｏｌ·Ｌ－１使ＡＰＡ和Ｖｍａｘ降低，动作电位时程及ＥＲＰ缩短，心肌收缩力加强。用药物阻滞钙通道，ＨｇＣｌ２改变动作电位的ＡＰＡ，Ｖｍａｘ，ＡＰＤ。ＨｇＣｌ２１０～２０μｍｏｌ·Ｌ－１增加哇巴因诱发的震荡后电位，使触发电活动增强。结论：ＨｇＣｌ２对心脏的毒性，可能通过其使心肌细胞内钙超负荷。     

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.     

Biodistribution characteristics of mannosylated and fucosylated O/W emulsions in mice

Cell-specific drug delivery is one of the most promising strategies for improving therapeutic efficiency and minimizing systemic toxicity. Carrier systems devoted to receptor-mediated targeting need to be developed. In the case of liver-non-parenchymal cell-specific targeting systems, glycosylated emulsions have been developed as carriers for lipophilic drugs and/or peptides. This present study demonstrates the in vivo disposition behaviour and pharmacokinetic characteristics of mannosylated (Man-) and fucosylated (Fuc-) emulsions incorporated with cholesten-5-yloxy-N-(4-((1-imino-2-d-thiomannosylethyl)amino)alkyl)formamide (Man-C4-Chol) and its fucosylated derivatives (Fuc-C4-Chol), respectively. Man- (or Fuc-) emulsions are composed of soybean oil, EggPC and Man-C4-Chol (or Fuc-C4-Chol) in a weight ratio of 70:25:5. After intravenous administration to mice, these two types of [³H]cholesteryl hexadecyl ether (CHE)-labelled glycosylated emulsions were rapidly eliminated from the blood circulation and preferentially recovered in the liver. In contrast, bare (Bare-) emulsions composed of soybean oil:EggPC:cholesterol (Chol) in a weight ratio of 70:25:5 were more retained in the blood circulation. The hepatic uptake clearances of Man- and Fuc-emulsions were 3.3- and 4.0-times greater than that of Bare-emulsions. Interestingly, the hepatic uptake clearance of Fuc-emulsions was significantly higher that that of Man-emulsions. The uptake ratios by non-parenchymal cells (NPC) and parenchymal cells (PC) (NPC/PC ratio) for Bare-, Man- and Fuc-emulsions were found to be 0.4, 2.0 and 2.9, respectively. The hepatic uptakes of [³H]CHE-labelled Man- and Fuc-emulsions were reduced by pre-dosing with glycosylated proteins and liposomes. These results clearly support the conclusion that Man- and Fuc-emulsions are promising carrier systems for liver NPC-specific targeting via receptor-mediated mechanism.     

小鼠骨髓来源树突状细胞对T细胞的活化作用

目的 从小鼠骨髓中体外诱导、扩增树突状细胞(DCs),检测DCs对T细胞的活化作用.方法 从小鼠骨髓中分离单个核细胞(MNCs),在重组鼠粒细胞-巨噬细胞集落因子(rmGM-CSF)、白细胞介素4(IL-4)和肿瘤坏死因子α(TNF-α)的诱导下培养扩增DCs.光学显微镜观察其形态特征,流式细胞仪分析其表型特征,混合淋巴细胞反应(MLR)检测DCs刺激同种异体T细胞增殖的能力.结果 MNCs经过rmGM-CSF、IL-4和TNF-α诱导培养12 d后,具有典型的DCs形态,高表达MHCⅡ类分子、CD11c、CD80、和CD86抗原.具有极强的激发刺激同种异体T细胞增殖的能力.结论 体外诱导、扩增DCs具有极强的激发刺激同种异体T细胞增殖的能力.     

Immunomodulatory activity of orphan drug Elmiron® in female B6C3F1/N mice

Interstitial cystitis (IC) is a chronic disorder characterized by bladder discomfort and urinary urgency in the absence of identifiable infection. Despite the expanding use in IC treatment and other chronic conditions, the effects of Elmiron® treatment on immune system remain unknown. Therefore, female B6C3F1/N mice were orally administered Elmiron® daily for 28-days at doses of 63, 125, 250, 500 or 1000 mg/kg to evaluate its immunomodulatory effects. Mice treated with Elmiron® had a significant increase in absolute numbers of splenic macrophages (63, 500 and 1000 mg/kg) and natural killer (NK) cells (250 and 1000 mg/kg). Elmiron® treatment did not affect the humoral immune response or T cell proliferative response. However, innate immune responses such as phagocytosis by liver macrophages (1000 mg/kg) and NK cell activity were enhanced (500 and 1000 mg/kg). Further analysis using a disease resistance model showed that Elmiron®-treated mice demonstrated significantly increased anti-tumor activity against B16F10 melanoma cells at the 500 and 1000 mg/kg doses. Collectively, we conclude that Elmiron® administration stimulates the immune system, increasing numbers of specific cell populations and enhancing macrophage phagocytosis and NK cell activity in female B6C3F1/N mice. This augmentation may have largely contributed to the reduced number of B16F10 melanoma tumors.     

乌贼墨对小鼠NK细胞杀伤活性的影响和抑瘤作用的研究

研究乌贼墨对小鼠脾细胞NK细胞杀伤活性的诱生作用及NK细胞杀伤性的持续时间，并探讨乌贼墨对荷瘤鼠脾细胞NK细胞杀伤活性的影响及抑制肿瘤生长的作用。用5％的乌贼墨给小鼠灌胃，连续5d后取不同时间的小鼠脾细胞，应用乳酸脱氢酶释放法检测NK细胞杀伤活性，结果表明，口服乌贼墨后可使小鼠NK细胞杀伤活性增强，实验组与对照组比较有显著性差异（P＜0．01），诱生后24h杀伤活性明显增强，2周左右恢复正常水平，乌贼墨可使荷瘤鼠NK细胞杀伤活性增强，瘤体明显小于阴性对照组，病理学分析证明小鼠瘤组织出血坏死及炎细胞浸润程度明显高于对照组，阳性对照组小鼠免疫功能损伤严重。     

珠蚌多糖对实验性移植肿瘤及NK细胞活性的作用

目的研究珠蚌多糖对实验性移植小鼠肿瘤以及对自然杀伤细胞（NK细胞）活性的影响。方法采用两种小鼠移植性肿瘤模型，观察珠蚌多糖对在体肿瘤细胞生长的影响；通过脾淋巴细胞与K562肿瘤细胞的共培养，体外检测NK细胞的活性。结果珠蚌多糖200，100mg·kg^-1对小鼠S180肉瘤的抑制率分别达到49．4％和47．1％，对C57BL／6小鼠B16BL6黑色素瘤的抑瘤率分别为39．1％和34．2％；显著提高S180肉瘤小鼠免疫脏器胸腺指数、脾指数；体外10，100μg·mL^-1珠蚌多糖可增强NK细胞对K562细胞的抑制活性。结论珠蚌多糖对实验移植性小鼠肿瘤生长有明显的抑制作用，体外一定剂量范围内可诱导NK细胞活性。     

Effects of imatinib mesylate on spontaneous electrical and mechanical activity in smooth muscle of the guinea-pig stomach

BACKGROUND AND PURPOSE: Effects of imatinib mesylate, a Kit receptor tyrosine kinase inhibitor, on spontaneous activity of interstitial cells of Cajal (ICC) and smooth muscles in the stomach were investigated. EXPERIMENTAL APPROACH: Effects of imatinib on spontaneous electrical and mechanical activity were investigated by measuring changes in the membrane potential and tension recorded from smooth muscles of the guinea-pig stomach. Its effects on spontaneous changes in intracellular concentration of Ca(2+) ([Ca(2+)](i)) (Ca(2+) transients) were also examined in fura-2-loaded preparations. KEY RESULTS: Imatinib (1-10 microM) suppressed spontaneous contractions and Ca(2+) transients. Simultaneous recordings of electrical and mechanical activity demonstrated that imatinib (1 microM) reduced the amplitude of spontaneous contractions without suppressing corresponding slow waves. In the presence of nifedipine (1 microM), imatinib (10 microM) reduced the duration of slow waves and follower potentials in the antrum and accelerated their generation, but had little affect on their amplitude. In contrast, imatinib reduced the amplitude of antral slow potentials and slow waves in the corpus. CONCLUSIONS AND IMPLICATIONS: Imatinib may suppress spontaneous contractions of gastric smooth muscles by inhibiting pathways that increase [Ca(2+)](i) in smooth muscles rather than by specifically inhibiting the activity of ICC. A high concentration of imatinib (10 microM) reduced the duration of slow waves or follower potentials in the antrum, which reflect activity of ICC distributed in the myenteric layers (ICC-MY), and suppressed antral slow potentials or corporal slow waves, which reflect activity of ICC within the muscle bundles (ICC-IM), presumably by inhibiting intracellular Ca(2+) handling.     

L—365，260翻转辛卡利特对抗吗啡对大鼠离体十二指肠电与机械活动的影响

目的:研究辛卡利特(CCK-8)的抗吗啡作用及其作用机制。方法:采用了同步描记大鼠离体十二指肠电与机械活动的方法。结果:乙酰胆碱(ACh,300nmol/L)可使大鼠离体十二指肠峰波振幅增大、数目增多,其收缩幅度随之增大,两者呈正相关。吗啡(330nmol/L)对离体十二指肠峰波的振幅、数目和收缩幅度均无明显影响,但能选择性抑制ACh对十二指肠段电与机械活动的加强作用,呈负相关。CCK-8(0.7nmol/L)本身对十二指肠段的电与收缩活动均无明显影响,但能选择性对抗吗啡的作用,即峰波振幅、数目再次增加,收缩幅度也随之增加。在此基础上,CCK-B受体拮抗剂L-365,260(30nmol/L)能翻转CCK-8的抗吗啡作用。结论:CCK-8能对抗吗啡抑制ACh加强十二指肠活动的作用,推测该作用是通过CCK-B受体实现的。     

Comparison of the effects of BRL 34915 and verapamil on electrical and mechanical activity in rat portal vein.

The effects of the novel anti-hypertensive agent BRL 34915, (+/-) 6-cyano-3,4-dihydro-2,2-dimethyl-trans-4-(2-oxo-1-pyrrolidyl)-2H-b enzo[b]pyran-3-ol, have been compared with those of verapamil on rat isolated portal vein. BRL 34915 produced a concentration-dependent reduction in mechanical responses to noradrenaline but had relatively little inhibitory effect on K+-induced contractions. Verapamil reduced the magnitude of both noradrenaline and K+-induced mechanical responses. BRL 34915 delayed the appearance of the reduced noradrenaline contractions, a property not shared by verapamil. BRL 34915 abolished spontaneous electrical and mechanical discharges and hyperpolarized the portal vein cells close to their calculated potassium equilibrium potential. Verapamil inhibited spontaneous electrical and mechanical discharges, effects associated with a small depolarization. BRL 34915 produced a significant increase in the 86Rb efflux rate coefficient whilst verapamil was without effect on this parameter. The inhibitory effects of BRL 34915 were rapid in onset and readily reversible by washing, whilst those of verapamil were slower in onset and only slowly reversible. It is concluded that the inhibitory effects of BRL 34915 in rat portal vein are produced by the opening of potassium channels in the smooth muscle cells. This inhibits spike activity and in sufficient concentration holds the membrane potential at or close to the potassium equilibrium potential, thereby reducing the effects of excitatory agents.