Effects of extracts of Portulaca oleracea on skeletal muscle in vitro

Extracts of Portulaca oleracea inhibited twitch tension due to direct (MS) and indirect electrical stimulation via the phrenic nerve (NS) of the rat hemidiaphragm muscle. The rank order of potency was dialysable extract greater than or equal to methanol extract greater than diethylether extract, although all exhibited equal efficacy. The non-dialysable extract did not inhibit twitch tension due to MS or NS. The dialysable, methanol and diethylether extracts inhibited tetanus tension, and attenuated the area under the K+- and caffeine-induced contracture. The contracture induced by nicotinic agonists and K+ on the rectus abdominis muscle was significantly inhibited by these extracts.     

Skeletal muscle relaxant properties of the aqueous extract of Portulaca oleracea

The skeletal muscle relaxant properties of an aqueous extract of Portulaca oleracea were examined on the twitch and tetanus tension evoked by electrical stimulation using the rat phrenic nerve-hemidiaphragm and frog sciatic nerve-sartorius muscle preparations and on contractures induced by nicotinic agonists using the rat rectus abdominis muscle preparation. The extract (5-50 X 10(-4) g/ml) produced a dose-dependent initial enhancement, followed by a longer lasting depression of twitch tension as induced by indirect electrical stimulation (NS) as well as direct stimulation (MS) of the diaphragm and sartorius muscle preparations. The augmentation of twitch amplitude (MS) produced by the extract was not significantly antagonised or potentiated by d-tubocurarine (5-50 X 10(-8) M) or physostigmine (5-50 X 10(-8) M) at concentrations which blocked or potentiated NS-induced twitch contractions. Furthermore, tetrodotoxin (5 X 10(-7) g/ml) alone or in combination with d-tubocurarine did not significantly attenuate extract-induced augmentation of twitch contractions to MS. In addition, the depression of twitch tension due to NS was not antagonised by physostigmine but was reversed and/or abolished by Ca2+ (2-5 X 10(-3) M) or potassium thiocyanate (1 X 10(-3) M). Contractures induced by K+ (80 mM) or by tetanic stimulation (20-60 Hz) were significantly reduced by the extract whereas, contracture induced by caffeine (2.5-6.0 mM) was not affected. Ca2+-free Tyrode's solution and EDTA (1.25 X 10(-3) g/ml) potentiated extract-induced depression of twitch tension to MS. On the rectus abdominis, contractures induced by nicotinic agonists (acetylcholine, 3-500 X 10(-7) M; carbachol, 5-500 X 10(-7) M and nicotine, 5-500 X 10(-8) M) were significantly attenuated and/or abolished by the extract (5-10 X 10(-3) g/ml). These observations indicate that the aqueous extract possesses unique skeletal muscle relaxant properties which do not appear to involve interference with cholinoceptor mechanism(s). It appears that the mechanism of action of the extract may involve interference with Ca2+ mobilization in skeletal muscle.     

Comparison of the skeletal muscle relaxant properties of Portulaca oleracea extracts with dantrolene sodium and methoxyverapamil

The effects of aqueous (AEE), dialysable (DIF) and methanol (MEE) extracts of Portulaca oleracea stems and leaves were compared with those of dantrolene sodium and methoxyverapamil (D-600) with respect to inhibition of twitch tension on the rat phrenic nerve-hemidiaphragm and with respect to contracture induced by nicotinic agonists on the frog rectus abdominis preparations. The extracts, dantrolene and D-600 inhibited twitch tension due to indirect electrical stimulation via the phrenic nerve (NS) on hemidiaphragm muscle, whereas the extracts and dantrolene inhibited, in addition, twitch amplitude due to direct muscle stimulation (MS). The extracts, dantrolene and D-600 also attenuated K+- and caffeine-induced contractures with the extracts and D-600 also reducing the time taken for the K+-induced contracture to fall to basal tension. In addition, the tetanic tension due to NS and MS was attenuated with only the extracts and dantrolene reducing the twitch/tetanus ratio (MS). There was a non-significant but consistent tendency for mutual potentiation between the extracts and dantrolene with respect to their inhibitory effect on twitch amplitude (MS) resulting in a shift to the left of the concentration-response curves to the extracts or dantrolene. This was not evident with the extracts and D-600 or dantrolene and D-600. Simultaneous addition of the extracts and dantrolene resulted in an increase in the rate of twitch tension inhibition and a decrease in the time to maximum relaxation of twitch amplitude (MS). The extracts and D-600 proved more effective in attenuating nicotinic agonist (acetylcholine, carbachol and nicotine)-induced contractures on the rectus abdominis muscle than dantrolene. From these observations, it appears that the Portulaca oleracea extracts mimic, in part, the effect of D-600 and dantrolene on the rat hemidiaphragm and frog rectus abdominis muscles; therefore, the muscle relaxant properties of the extracts may be due, in part, to inhibition of trans-membrane Ca influx, interference with the Ca-induced Ca release process and/or inhibition of the release of intracellular Ca from stores in the sarcoplasmic reticulum.     

Effects of leaf extract of Caesalpinia bonduc (Caesalpiniaceae) on the contractile activity of uterine smooth muscle of pregnant rats

The calcium dependency and the cholinergic effect of the leaf extract of Caesalpinia bonduc Roxb. (Caesalpiniaceae) was studied in isolated pregnant rat myometrium preparations. Isometric contractions were recorded. The extract (Cebo) increased the contractile force in the isolated strips in a concentration-dependent manner. The effects were comparable to those obtained with acetylcholine. Contractions induced by Cebo or acetylcholine were inhibited in the presence of atropine. The stimulating action of Cebo on the contractile responses of isolated myometrium preparations inhibited by atropine may be mediated by cholinergic receptors. In calcium-free solution Cebo induced a tonic contraction (contracture) of the muscle. Moreover, in high-potassium calcium-free solution Cebo caused contracture of the uterine smooth muscle. Cebo was still able to elicit contractions in calcium-free solution containing EDTA or EGTA. These findings suggest the existence of cholinergic receptors sensitive to Cebo which could influence the influx of calcium (phasic contraction) and mobilization of calcium from cellular stores (tonic contraction), both of which are responsible for the increase of contractile activity and development of the contracture of uterine smooth muscle.     

Pycnogenol Cytotoxicity in Pancreatic INS‐1E β cells Induced by Calcium Dysregulation

Natural standardized flavonoid extract from the bark of Pinus pinaster, Pycnogenol (Pyc), was recently found to decrease intensively the activity of sarcoplasmic reticulum Ca²⁺‐ATPase of rabbit skeletal muscle (SERCA1). On the basis of this inhibitory effect in a cell‐free system and similarities of SERCA1 to its other isoforms, proapoptotic properties of Pyc may be expected in cellular systems. Pycnogenol (40–100 μg/mL) induced a concentration‐dependent decrease of the viability of pancreatic INS‐1E β cells associated with induction of apoptosis. In addition, intracellular Ca²⁺ level increase was found along with reduction of protein expression level of SERCA2b and impairment of insulin secretion by β cells. These facts indicate that Pyc may induce apoptosis by impairment of calcium homeostasis. Copyright © 2017 John Wiley & Sons, Ltd.     

Mechanisms of Vasorelaxation Induced by Hexahydrocurcuminin Isolated Rat Thoracic Aorta

This study was designed to examine the vasorelaxant effects of hexahydrocurcumin (HHC), one of the major natural metabolites of curcumin from Curcuma longa, on rat isolated aortic rings, and the underlying mechanisms. Isometric tension of the aortic rings was recorded using organ bath system. HHC (1 nM to 1 mM) relaxed the endothelium‐intact aortic rings pre‐contracted with PE and KCl in a concentration‐dependent manner. Removal of the endothelium did not alter the effect of HHC‐induced relaxation. In Ca²⁺‐free Krebs solution, HHC significantly inhibited the CaCl₂‐induced contraction in high K⁺ depolarized rings and suppressed the transient contraction induced by PE and caffeine in a concentration‐dependent manner. HHC was also observed to relax phobal‐12‐myristate‐13‐acetate (PMA), an activator of protein kinase C (PKC), precontracted aortic rings in a concentration‐dependent manner with EC₅₀ values equivalent to 93.36 ± 1.03 μM. In addition, pre‐incubation with propranolol (a β‐adrenergic receptor blocker) significantly attenuated the HHC‐induced vasorelaxation. These results suggest that the vasorelaxant effect of HHC is mediated by the endothelium‐independent pathway, probably because of the inhibition of extracellular Ca²⁺ influx through voltage‐operated Ca²⁺ channels and receptor‐operated Ca²⁺ channels, the inhibition of Ca²⁺mobilization from intracellular stores, as well as inhibition of PKC‐mediated Ca²⁺‐independent contraction. Moreover, HHC produces vasorelaxant effects probably by stimulating the β‐adrenergic receptor. Copyright © 2015 John Wiley & Sons, Ltd.     

Insulinotropic activity of Tinospora crispa extract: effect on ß-cell Ca2+ handling

The mechanism of insulinotropic action of Tinospora crispa was investigated in vitro using an insulin-secreting clonal ß-cell line, HIT-T15. The aqueous extract sensitizes the ß-cell to extracellular Ca²⁺ and promotes intracellular Ca²⁺ accumulation which in turn causes increased insulin release. The increase in cytosolic Ca²⁺ concentration is due to stimulation of Ca²⁺ uptake from the extracellular medium and inhibition of Ca²⁺ efflux from the cytosol. That the mechanism of insulinotropic action of T. crispa is physiological suggests that the insulin secretagogue/s present in the extract could indeed be a potential source of a specific oral hypoglycaemic agent for the treatment of non-insulin-dependent diabetes mellitus. © 1998 John Wiley & Sons, Ltd.     

灵芝多糖对小鼠腹腔巨噬细胞胞浆游离Ca2+浓度的影响

 目的:探讨灵芝多糖(GLP)对免疫细胞信号转导过程的影响?方法:采用激光扫描共聚焦显微镜(LSCM)技术,动态监测GLP均一体组分GLB₇对小鼠腹腔巨噬细胞(MΦ)胞浆游离Ca²⁺浓度([Ca²⁺]i)的影响?结果:GLB₇(20μg·ml^-1)引起小鼠腹腔MΦ中[Ca²⁺]i明显升高,升高值为(248±18)%(n=6);GLB₇引起小鼠腹腔MΦ外钙内流及MΦ内IP₃敏感和IP₃非敏感钙池释放Ca²⁺,[Ca²⁺]i升高值分别为(76±10)%,(58±10)%,(41±8)%(n=6);GLB₇对MΦ[Ca²⁺]i的影响与K⁺通道及其引起的膜电位变化无关?结论:MΦ是灵芝多糖作用的靶细胞;GLB₇引起MΦ中[Ca²⁺]i快速升高,可能是灵芝多糖产生作用的重要途径?     

瓜蒌皮提取物对大鼠主动脉PDC Ca2+内流的影响

为了研究瓜蒌皮治疗冠心病的有效成分,用醚醇法和水煎醇沉法提取瓜蒌皮的有效成分,并用⁴⁵Ca跨膜测量方法研究各提取物对大鼠主动脉PDC钙通道Ca²⁺内流的影响。发现氯仿和醇溶物能阻滞Ca²⁺内流,水溶物具有相反的作用,其中氯仿提取物浓度为30 mg/mL时,使Ca²⁺内流量比对照下降31.57%。实验结果表明瓜蒌皮中可能有7种组分具有治疗冠心病的活性。     

白藜芦醇对大鼠离体胸主动脉环的舒张作用

目的:观察白藜芦醇(resveratrol,RVL)对大鼠离体胸主动脉血管的舒张作用并探讨其机制。方法:采用离体血管环灌流方法,观察RVL在含Ca²⁺或无Ca²⁺ Krebs液孵育条件下对去甲肾上腺素(NA)引起的血管平滑肌收缩的影响;同法观察RVL对30,80mmol·L^-1的KCl引起的血管平滑肌收缩的影响;RVL对NA引起的依赖于细胞内钙和细胞外钙收缩反应的影响,以及加入N-G-硝基-L-精氨酸(L-NNA)和优降糖后RVL舒张大鼠离体主动脉环效应的变化。结果:RVL呈浓度依赖性舒张NA引起的血管收缩;无Ca²⁺ 组RVL抑制NA所致血管平滑肌收缩效应大于含Ca²⁺ 组;RVL能够拮抗NA诱发的依内钙的收缩反应,而对外钙收缩无抑制。RVL对80,30mmol·L^-1 的KCl引起的血管平滑肌收缩均有抑制作用,且前者量效曲线明显上移。L-NNA使RVL舒血管效应降低(26.0±4.6)%;优降糖组的血管舒张受抑程度与对照组无显著差别(P>0.05)。结论:RVL可呈内皮依赖性舒张血管平滑肌,其作用机制可能与该药促进NO合成释放,开放钙激活的钾通道以及抑制血管平滑肌细胞外钙内流和内钙释放有关。     

益心酮调控细胞膜钙通道的实验研究

目的 :观察中药益心酮片调控细胞膜钙通道的特性 ,从细胞和亚细胞水平探讨其改善心肌缺血再灌注损伤的作用机理。方法 :采用大鼠主动脉平滑肌细胞模型 ,用放射性⁴⁵Ca跨膜流动测定技术分别观察益心酮片对溢流钙通道 (LC)、受体调控钙通道 (ROC)和电压依赖钙通道 (PDC)Ca²⁺ 内流的影响。结果 :益心酮片对LCCa²⁺ 内流无明显影响 ,对ROC和PDCCa²⁺ 内流有明显抑制作用。结论 :益心酮可以抑制慢通道Ca²⁺ 内流 ,且抑制作用呈现剂量依赖关系。     

Relaxant effect of flavonoid naringenin on contractile activity of rat colonic smooth muscle

Ethnopharmacological relevance

Disturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility.

Material and methods

Mechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca²⁺] concentration ([Ca²⁺]_i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo.

Results

Naringenin induced a concentration-dependent inhibition (1–1000 μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca²⁺ influx induced contraction and [Ca²⁺]_i increase were inhibited by naringenin (100 μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K⁺ (BK_Ca) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BK_Ca current, which was insensitive to changes in the [Ca²⁺]_i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo.

Conclusion

Our results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BK_Ca channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca²⁺ influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.     

胡颓子叶对豚鼠离体气管平滑肌收缩功能的影响

目的 研究胡颓子叶乙醇提取物正丁醇部位(胡颓子叶正丁醇部位)对正常及多种致痉剂诱导的豚鼠气管平滑肌收缩功能的影响.方法 制备豚鼠离体气管平滑肌螺旋条,在其正常状态下以及用乙酰胆碱、组胺、氯化钾、无钙下乙酰胆碱诱导细胞内钙释放和高钙下诱发细胞外钙内流条件下,观察胡颓子叶正丁醇部位对离体气管张力的影响.结果 胡颓子叶正丁醇部位对静息状态下的豚鼠离体气管平滑肌有明显的舒张作用,使乙酰胆碱和组胺的量效曲线发生明显右移,抑制加入高钾或高钙后引发细胞外钙内流导致的收缩.结论 胡颓子叶正丁醇部位能明显抑制正常状态及多种致痉剂诱发的豚鼠气管平滑肌收缩.     

M3 muscarinic receptor- and Ca influx-mediated muscle contractions induced by croton oil in isolated rabbit jejunum

Aim of study

Croton oil is the fruit oil of Croton tiglium L., which is well known in folk medicine for the treatment of gastrointestinal (GI) diseases, including constipation, abdominal pain, peptic ulcer, and intestinal inflammation for a long period. This study was to investigate the pharmacological effect of croton oil on GI tract.

Materials and methods

The effect of croton oil on the smooth muscle contractions was investigated in vitro using the isolated rabbit jejunum model.

Results

Croton oil has a biphasic action contracting and relaxing intestinal tissue. At the concentrations of 20–80 μg/mL, croton oil produced a concentration-dependent increase in the amplitude and tension of muscle contractions, whereas at high concentrations (>200 μg/mL) it decreased the contractile amplitude and had no impact on the tension. Moreover, croton oil was less effective in increasing muscle amplitude and tension than Ach, confirming that the effect of croton oil on muscle contractions is not a simply stimulatory or inhibitory action, but a unique modulatory process depending on the concentration of croton oil. In addition, croton oil concentration-dependently suppressed the frequency of muscle contractions. On the other hand, atropine (10 μM) and 4-DAMP (10 μM) produced a significant inhibition of contractions caused by croton oil, while either hexamethonium (10 μM) or methoctramine (10 μM) was inactive, implying that the regulatory effects of croton oil on GI motility are mediated via the activation of M3 muscarinic receptor. Furthermore, muscle contractions induced by croton oil were dramatically reduced by verapamil (0.1 μM) but not by NE (1 μM), suggesting that the action of croton oil on GI motility is also mediated by Ca²⁺ influx through L-type Ca²⁺ channel.

Conclusions

The results suggest that croton oil possesses spasmogenic and spasmolytic properties and the regulatory effects of croton oil on GI motility are mediated via the activation of M3 muscarinic receptor and Ca²⁺ influx through L-type Ca²⁺ channel.     

葛根素对氧糖剥夺大鼠海马神经细胞Ca2+和NO的影响

 目的研究葛根素(puerarin,Pur)对缺氧缺糖状态下海马神经细胞内Ca²⁺和NO水平的影响。方法选用新生大鼠体外培养8 d的海马神经细胞,进行3 h的氧糖剥夺(oxygen/glucose deprivation,OGD)或30 min的L-谷氨酸(0.5mmol·L^-1)处理后再正常培养24 h,Pur处理组在OGD或谷氨酸处理的同时和以后24 h给予不同剂量(40,100μmol·L^-1)Pur,Annexin V联合流式细胞仪检测细胞的凋亡率和坏死率;以Fluo-3或DAF-2为荧光标记,用激光共聚焦显微镜观测30 min的OGD过程中海马神经细胞Ca²⁺和NO的动态变化以及Pur的影响。结果OGD诱导海马神经细胞Ca²⁺和NO水平快速升高,其最高值分别达正常对照组的2.9和1.9倍;Pur明显减缓OGD期间神经细胞Ca²⁺内流和NO合成,与OGD组相比,40和100μmol·L^-1的Pur分别使细胞Ca²⁺峰值降低29.2%和37.1%(P<0.05和P<0.01),NO峰值降低23%和33%(P<0.05和P<0.01),显著抑制细胞内Ca²⁺和NO水平的升高;同时Pur可有效抑制OGD和谷氨酸引起的神经细胞死亡。结论Pur可通过抑制神经细胞谷氨酸/Ca²⁺/NO通路的活动而有效保护缺氧缺糖对神经细胞的损伤作用。     

大黄素和大黄多糖对小鼠脾淋巴细胞内游离钙浓度的影响

应用最新一代钙离子荧光指示剂ｕｒａ－２／ＡＭ测定小鼠脾淋巴细胞内游离钙浓度，探讨大黄有效成分蒽醌类中大黄素和大黄多糖对脾淋巴细胞内游离钙的影响。实验表明：大黄素（终浓度１８．５μｍｏｌ／Ｌ）对淋巴细胞外钙内流有明显促进作用（Ｐ＜０．０１）；大黄多糖则有抑制内钙释放和外钙内流（Ｐ＜０．０１），且抑制程度与剂量相关。本文为大黄双向调节作用提供理论依据。     

隔山香正丁醇部位对大鼠胸主动脉的舒张作用及机制的影响

目的:研究隔山香(Lemonfragrant Angelica Root,LAR)正丁醇部位对大鼠胸主动脉环的舒张作用,并探讨其可能的作用机制。方法:采用离体大鼠胸主动脉血管环灌流方法,考察0.34,0.65,1.22 g·L-1隔山香正丁醇部位对氯化钾(KCl)和去甲肾上腺素(norepinephrine,NE)预收缩的血管环张力的影响。在无Ca2+Kreb’s液中,考察0.34,0.65,1.22 g·L-1隔山香正丁醇部位对氯化钙(Ca Cl2)量效曲线的影响和NE预收缩的血管环张力的影响。激光共聚焦扫描显微镜检测平滑肌细胞内[Ca2+]i的变化。结果:隔山香正丁醇部位对KCl和NE预收缩的内皮完整和去除内皮血管环均具有浓度依赖性的舒张作用(P0.01),并且去除内皮后的舒张作用未受影响;无Ca2+条件下,隔山香正丁醇部位能使Ca Cl2,NE预收缩强度显著性降低(P0.01)。激光共聚焦扫描显微镜下,隔山香正丁醇部位(1.22 g·L-1)能抑制KCl,NE和毒胡萝卜素(thapsigargin,TG)引起的平滑肌细胞内[Ca2+]i升高。结论:隔山香正丁醇部位对大鼠胸主动脉血管有一定的舒张作用,可能通过抑制外钙内流和内钙释放发挥作用。本实验为隔山香水蒸气蒸馏后煎煮入药的成药制备工艺和水溶性药效指标成分的分离提供了依据。     

环维黄杨星D对心肌细胞缺氧/复氧损伤的保护作用和对心肌细胞内游离钙浓度的影响

目的:研究环维黄杨星D(CVB-D)对培养乳鼠心肌细胞缺氧/复氧损伤的保护作用和对急性分离大鼠心肌细胞内游离Ca²⁺浓度的影响。方法:采用培养的乳鼠心肌细胞建立缺氧/复氧损伤模型,测定心肌细胞搏动频率、细胞存活率、肌酸激酶(CK)的含量;应用特异性荧光指示剂Fluo-3/AM负载急性分离的大鼠心肌细胞,用激光共聚焦显微镜检测胞内游离钙的变化。结果:缺氧/复氧损伤+环维黄杨星D组(H/R+CVB-D)乳鼠心肌细胞搏动频率、细胞存活率与缺氧/复氧损伤组比较明显升高,CK含量与缺氧/复氧损伤组比较明显下降。对急性分离大鼠心肌细胞内[Ca²⁺]i逐步升高,并呈剂量依赖性;在有外钙和无外钙时,CVB-D对胞内钙的升高有显著差异(P<0.05);在无外钙并加入内罗啶孵育后,CVB-D引起的胞内[Ca²⁺]i轻度升高,但与无钙组相比无显著性差异(P>0.05)。结论:环维黄杨星D对培养乳鼠心肌细胞缺氧/复氧损伤有保护作用,对急性分离大鼠有升高心肌细胞内游离钙离子浓度的作用,[Ca²⁺]的升高既源于内钙释放又源于外钙内流。     

Dual effects of lipophilic extract of Salvia miltiorrhiza (Danshen) on catecholamine secretion in cultured bovine adrenal medullary cells

Ethnopharmacological relevance

Salvia miltiorrhiza (Danshen) is a well known traditional Chinese herb, which has been used widely in China for the treatment of cardiovascular diseases in clinic.

Aim of this study

The aim of the present study is to clarify the effects of lipophilic extract of Salvia miltiorrhiza (LESM) on catecholamine (CA) secretion, a traditional Chinese medicine used widely for the treatment of cardiovascular diseases in China.

Materials and methods

LESM was evaluated for its effects on CA secretion using HPLC-ECD method. The effects of LESM on ²²Na⁺ influx and intracellular calcium ([Ca²⁺]_i) were also investigated.

Results

Our results showed that LEMS directly stimulated basal CA secretion in an extracellular Ca²⁺-dependent manner. And the stimulation was not affected by combination of hexamethonium (Hex), an inhibitor of nAChR. LESM also directly elevated [Ca²⁺]_i. In addition, using selective blockers of voltage-dependent Ca²⁺ channels, such as nitrendipine (for L-type), ω-agatoxin-IVA (for P-type) and ω-conotoxin-GVIA (for N-type), it was found that nitrendipine suppressed the elevation of [Ca²⁺]_i induced by LESM, but not ω-agatoxin-IVA or ω-conotoxin-GVIA. Compared with acetylcholine (ACh) only, however, combination of LESM with ACh inhibited the raise of CA secretion, ²²Na⁺ influx and [Ca²⁺]_i in a concentration-dependent manner. Furthermore, LESM also inhibited CA secretion induced by veratridine (Ver), and 56 mM K⁺ at concentrations similar to those for [Ca²⁺]_i rise. One of the lipophilic active compounds, cryptotanshione (Cryp), also had the same effects on CA secretion with LESM.

Conclusions

All these findings suggest that LESM exerts dual effects on CA secretion in cultured bovine adrenal medullary cells. LESM exerts antagonistic effects on nAChR, voltage-dependent Na⁺ and Ca²⁺ channels, whereas it is an agonist of L-type Ca²⁺ channel when it used alone.     

Effects of extracts of seed and leaf of Piper guineense on skeletal muscle activity in rat and frog

The pharmacological effects of leaf and seed extracts of Piper guineense were investigated on phrenic nerve hemidiaphragm activity following electrical stimulation in vitro. The Leaf and seed extracts (10 micrograms-1 mg/mL) and (50-800 micrograms/mL) respectively produced biphasic effects consisting of an initial enhancement followed by secondary transient or prolonged depression of twitch tension in response to electrical stimulation of both muscle and nerve. These effects were similar to that of decamethonium (2-800 mg/mL). An increased concentration of extracellular Ca2+ in vitro reversed the twitch contraction inhibited by the leaf and seed extracts in a dose related pattern following electrical stimulation. It is concluded that the leaf and seed extracts of Piper guineense possess among other pharmacological properties, a depolarizing neuromuscular blocking action.