Mitochondrial uncoupler triclosan induces vasorelaxation of rat arteries

Our previous studies found that mitochondrial uncouplers induced vasodilation. Triclosan, the broad spectrum antibacterial agent, is the active ingredient in soaps and toothpastes. It was reported that triclosan induced mitochondrial uncoupling, so we aim to investigate the effects of triclosan on vascular function of rat mesenteric arteries and aorta. The isometric tension of rat mesenteric artery and thoracic aorta was recorded by multi-wire myograph system. The cytosolic [Ca²⁺]_i, mitochondrial reactive oxygen species (mitoROS), and mitochondrial membrane potential of smooth muscle cells (A10 cells) were measured using laser scanning confocal microscopy. Triclosan treatment relaxed phenylephrine (PE)- and high K⁺ (KPSS)-induced constriction, and pre-treatment with triclosan inhibited PE- and KPSS-induced constriction of rat mesenteric arteries. In rat thoracic aorta, triclosan also relaxed PE- and KPSS-induced constriction. Triclosan induces vasorelaxation without involving K_ATP channel activation in smooth muscle cells of arteries. Triclosan treatment increased cytosolic [Ca²⁺]_i, mitochondrial ROS production and depolarized mitochondrial membrane potential in A10 cells. In conclusion, triclosan induces mitochondrial uncoupling in vascular smooth muscle cells and relaxes the constricted rat mesenteric arteries and aorta of rats. The present results suggest that triclosan would indicate vasodilation effect if absorbed excessively in vivo.     

心喘灵(XC-1)及其衍生物XC-2对肾上腺素受体及动脉平滑肌的作用

本文用放射配基结合法研究了心喘灵(XC-1)及其衍生物XC-2对肾上腺素受体的亲和力,用离体器官方法观察了二者对α受体功能的影响,用酶分析法研究了两药对β受体功能的影响。两药各种作用强度相近,对大鼠脑皮层细胞膜α受体有中等强度亲和力(Ki10^-6mol/L),对兔主动脉和大鼠肛尾肌α₁受体均有中等强度阻断作用,但对大鼠输精管突触前α₂受体只有微弱的阻断作用。二药抑制由ISO激动的腺苷酸环化酶活性的IC₅₀均为3.6×10^-5mol/L。此外,二者都能拮抗CaCl₂,KCl和5-HT引起的主动脉条收缩反应并有直接扩张血管的作用。     

Angiotensin II-induced increase in slowly exchanging 45Ca2+ in relation to contractile responses of rat and guinea-pig aorta

Summary To gain more information about sources of activator Ca²⁺ involved in the contraction of rat and guinea-pig aorta evoked by angiotensin II and their sensitivity to Ca ²⁺ entry blockers, measurement of slowly exchanging ⁴⁵Ca²⁺ was established. A more physiological procedure was used, replacing La³⁺- and EGTA- containing solutions by a normal Ca²⁺-containing buffer. It was demonstrated that the angiotensin 11-induced increase in slowly exchanging ⁴⁵Ca²⁺ in rat aorta was incompletely (by approximately 60%–70%) inhibited by the organic Ca²⁺ entry blockers nifedipine, verapamil and diltiazem and by other Ca⁺ entry blocking compounds like CoCl₂ and chlorpromazine. 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) was able to inhibit the angiotensin II-induced increase in ⁴⁵Ca²⁺ content completely, but this may be an intracellular storage effects. By contrast, the organic Ca²⁺ entry blockers completely inhibited that part of the angiotensin II-induced contraction of rat aorta which was dependent upon extracellular Ca²⁺.In guinea-pig aorta, the increase in ⁴⁵Ca²⁺ content elicited by angiotensin 11 could be completely suppressed by all compounds under study. The results of these experiments correlated well with data from the functional experiments in guinea-pig aorta. In both preparations the release of Ca ²⁺ from a rapidly as well as a slowly exchanging intracellular pool appears to contribute to the contractile response elicited by angiotensin 11. Offprint requests to P. N. M. van Heiningen at the above address     

Inhibition of calcium influx in rabbit aorta by nicardipine hydrochloride (YC-93)

The Ca²⁺ antagonistic effects of a potent vasodilator, nicardipine hydrochloride [2-(N-benzyl-N-methylamino)ethyl methyl 2,6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate hydrochloride], were investigated. Both nicardipine and verapamil, neither of which exhibited a significant effect on cellular ⁴⁵Ca²⁺ uptake by the rabbit aorta in normal buffer containing 2.68 mM KCl as measured by the “lanthanum method”, inhibited the enhancement of ⁴⁵Ca²⁺ uptake induced by equimolar replacement of 120 mM NaCl by KCl. Nicardipine with an ic₅₀ (the concentration required for 50 per cent inhibition) of 10^?9 M was sixty-eight times more potent than verapamil in the inhibition of KCl-induced ⁴⁵Ca²⁺ uptake. Nicardipine also repressed KCl-induced contraction of the aorta and its ic₅₀ was about 2 × 10^?9M, eighty-five times smaller than that of verapamil. These comparative studies on the relation between cellular ⁴⁵Ca²⁺ uptake and KCl-induced contraction of the rabbit aorta suggest that nicardipine causes relaxation of smooth muscle mainly by interfering with Ca²⁺ influx.     

The vasodilator papaverine stimulates L-type Ca2+ current in rat tail artery myocytes via a PKA-dependent mechanism

Papaverine is an opium alkaloid, primarily used as an antispasmodic drug and as a cerebral and coronary vasodilator. Its phosphodiesterase inhibitory activity promotes increase of cAMP levels mainly in the cytosol. As cAMP is known to modulate L-type Ca²⁺ channel activity, here we tested the proposition that papaverine could affect vascular channel function. An in-depth analysis of the effect of papaverine on Ba²⁺ or Ca²⁺ current through L-type Ca²⁺ channel [I_Ba(L) or I_Ca(L)], performed in rat tail artery myocytes using either the whole-cell or the perforated patch-clamp method, was accompanied by a functional study on rat aorta rings. Papaverine increased current amplitude under both the perforated or whole-cell configuration. Stimulation of the current by papaverine was concentration-, V_h-, frequency-, and charge carrier-dependent, and fully reverted by drug washout. The PKA inhibitor H89, but not the PKG inhibitor Rp-8-Br-cGMPS, antagonised papaverine- as well as IBMX- (another phosphodiesterase inhibitor) induced I_Ba(L) stimulation. In cells pre-treated with IBMX, application of papaverine failed to increase current amplitude. Papaverine sped up the inactivation kinetics of I_Ba(L), though only at concentrations ≥ 30 μM, and shifted the voltage dependence of the inactivation curve to more negative potentials. In rings, the vasorelaxing activity of papaverine was enhanced by previous treatment with nifedipine. In conclusion, papaverine stimulates vascular L-type Ca²⁺ channel via a PKA-dependent mechanism, thus antagonising its main vasodilating activity.     

RELATIVE CONTRIBUTIONS OF EXTRACELLULAR Ca2+ AND Ca2+ STORES TO SMOOTH MUSCLE CONTRACTION IN ARTERIES AND ARTERIOLES OF RAT, GUINEA-PIG DOG AND RABBIT

1. These studies describe the functional effects of modulation of the sarcoplasmic reticulum (SR) Ca²⁺ stores at three levels of the vasculature: (i) large arteries (rat and guinea-pig aorta); (ii) small resistance arteries (rat tail artery, rabbit mesenteric artery, dog mesenteric artery); and (iii) arterioles (guinea-pig submucosal arterioles of the small intestine). 2. All tissues responded to phenylephrine (PE; 10 μmol/L) with a transient contraction in Ca²⁺-free Krebs', reflecting Ca²⁺ release from PE-sensitive Ca²⁺ stores. After pretreatment with cyclopiazonic acid (CPA; 30 μmol/L) or thapsigargin (TSG; 1 μmol/L), putative SR Ca²⁺ pump inhibitors, the PE-induced contraction in a Ca²⁺-free medium was significantly inhibited in arterial tissues at all levels of the vasculature. Similarly, ryanodine (RYA; 30 μmol/L), an agonist that enhances Ca²⁺ release from the SR, also reduced the PE contraction in a Ca²⁺-free solution. 3. CPA or TSG alone in the presence of extracellular Ca²⁺, caused marked and sustained contraction in the rat and guinea-pig aorta and marked but transient or no contraction in the resistance arteries. In the rat and guinea-pig aorta, RYA caused a slowly developing tension. Little increase in basal tension was produced by RYA in resistance arteries and arterioles. 4. The findings show that an agonist-releasable Ca²⁺ pool is present at all levels of the vasculature that is independent of the size of the vessels and suggest that under normal physiological conditions there is an intimate balance between the roles of the plasma membrane and of the SR in the maintenance of vascular contractility. It appears that the role of the SR diminishes as the arteries become smaller, while Ca²⁺ fluxes across the plasma membrane predominates.     

Effects of Terbutaline on α-Adrenergic Responses and Ca2+ Influx in Isolated Rabbit Aorta

Effects of terbutaline applied in vivo or in vitro on α-adrenergic receptors in the rabbit aorta in normal and Ca²⁺–free solution, and on basal, high potassium-, and phenylephrine-stimulated Ca²⁺ uptake into aorta were investigated. Three day terbutaline administration (25 mg/kg, subcutaneously three times daily) to rabbits increased the pK_B for phentolamine in aorta rings (control 7.3 + 0.2, n = 9; terbutaline 7.8 +0.2, n = 15). It also depressed phenylephrine-stimulated contractions of aorta rings in Ca²⁺–free but not those in normal Krebs solution. It did not significantly depress the basal, or phenylephrine-evoked Ca²⁺ influx into aorta rings, but decreased high potassium-induced Ca²⁺–influx (control 0.58 + 0.05 umoles/g aorta; n = 3, terbutaline 0.41 +0.06 umoles/g aorta, n = 3). In vitro application of 50 μM terbutaline did not significantly alter phenylephrine-stimulated contractions of aorta rings in Ca²⁺–free Krebs solution or significantly depress basal or phenylephrine-induced Ca²⁺ influx into aortas, but did decrease high potassium-stimulated Ca²⁺–influx. Thus, 3-day terbutaline administration increased the affinity of α-adrenergic receptors for phentolamine and had a tendency to increase contractions of aorta rings to phenylephrine. It also decreased high potassium-stimulated Ca²⁺ influx, and depressed phenylephrine-induced contractions in Ca²⁺–free Krebs solution, while in vitro terbutaline application also decreased potassium-induced Ca²⁺ influx.     

Studies on the Mechanism of Spasmolytic Activity of (O-Methyl-)-N-(2,6-dihydroxybenzoyl)tyramine,a Constituent of Aniba riparia (Nees) Mez. (Lauraceae), in Rat Uterus,Rabbit Aorta and Guinea-pig Alveolar Leucocytes

Abstract— The mechanism of action of a nonspecific smooth muscle relaxant, (O-methyl-)-N-(2,6-dihydroxybenzoyl)tyramine (riparin), a constituent of Aniba riparia (Nees) Mez. (Lauraceae) was studied in relation to Ca²⁺ metabolism in smooth muscle tissues and in guinea-pig alveolar leucocytes. In rat depolarized uterus, riparin inhibited in a reversible and noncompetitive manner CaCl₂-induced contraction, a response mediated through voltage-dependent Ca²⁺ channels. The pD₂ value (mean±s.e.m.) for riparin was 4·98±006. When compared with sodium nitroprusside (IC50 2·5 μm ), an antagonist of receptor-operated Ca²⁺ channels, riparin was ineffective in suppressing noradrenaline-induced sustained contractions of rabbit aortic strips. However, in the aorta, the compound inhibited intracellular calcium-dependent transient contractions of noradrenaline and riparin (IC50 10·1 μm ), was approximately two and a half times more potent than procaine (IC50 25·5 μm ), a known inhibitor. In guinea-pig alveolar leucocytes, riparin (IC50 3·2 μm ), inhibited intracellular Ca²⁺ accumulation induced by the calcium ionophore A23187. The results suggest that the inhibition of Ca²⁺ influx and of Ca²⁺ release from intracellular stores contribute to the spasmolytic effects of riparin, which may not involve cyclic AMP generation as the levels of this nucleotide were not increased in alveolar macrophages treated with riparin (10–100 μm ).     

Chalcones as potent antiplatelet agents and calcium channel blockers

In an effort to continually develop potent antiplatelet agents with vasorelaxing and antiinflammatory actions, a novel series of antiinflammatory chalcones was continually screened to evaluate their antiplatelet and vasorelaxing effects. Their structure–activity relationships and mode of action were discussed and characterized. A novel series of antiinflammatory chalcones was studied on antiplatelet effect in rabbit washed platelets and human platelet‐rich plasma (PRP) and vasorelaxing effect in rat thoracic aorta. Arachidonic acid‐induced platelet aggregation was potently inhibited by almost all the chalcone derivatives and 13–15 also had a potent inhibitory effect on cyclooxygenase. The selective chalcones 12–16 tested in human PRP significantly inhibited secondary aggregation induced by adrenaline. In rat thoracic aorta, most of chalcones at high concentration significantly depressed the contractions induced by Ca²⁺ (1.9 mM) in high K⁺ (80 mM) medium and the phasic and tonic contractions caused by norepinephrine (3 μM). In the rat thoracic aorta, the phenylephrine‐ and high K⁺‐induced ⁴⁵Ca²⁺ influx were both inhibited by a selective chalcone derivative, 14 . These results indicate that the antiplatelet actions of chalcones are mainly mediated through the suppression of cyclooxygenase activity and reduced thromboxane formation and their inhibitory effects on the contractile response caused by high K⁺ and norepinephrine in rat thoracic aorta are mainly due to inhibition of Ca²⁺ influx through both voltage‐dependent and receptor‐operated Ca²⁺ channels. Drug Dev. Res. 53:9–14, 2001. © 2001 Wiley‐Liss, Inc.     

Evidence for a direct interaction of thapsigargin with voltage-dependent Ca2+ channel

The effect of thapsigargin, an inhibitor of the sarco-endoplasmic reticulum Ca²⁺-ATPase, on voltage-dependent Ca²⁺ channels has been investigated in the A7r5 cell line and in membrane preparations from rat aorta, heart and brain. Patch-clamp technique showed that, at micromolar concentrations, thapsigargin inhibited the L-type Ca²⁺ channel current in A7r5 cells. It depressed the current at all voltages without change in the steady state inactivation curve. The rates of inactivation of the Ca²⁺ current were highly variable among the cells suggesting that more than one component of L-type Ca²⁺ current coexist in A7r5 cells, differing in the kinetics of inactivation. Thapsigargin appeared to be more potent on the slower-inactivating Ca²⁺ current than on the faster-inactivating one. In the same range of concentrations, thapsigargin inhibited the specific binding of ³H(+)-isradipine in intact cells while ⁴⁵Ca²⁺ uptake in intracellular stores of skinned cells was inhibited at nanomolar concentrations. The equilibrium dissociation constant of ³H(+)-isradipine was increased in the presence of thapsigargin as a result of an increase of the dissociation rate constant indicating that the inhibitory effect of the antagonist cannot be attributed to a simple competitive interaction with the dihydropyridine binding site. Maximum binding capacity was unaffected. A similar pattern of inhibition of ³H(+)-isradipine binding was observed in membrane preparations from rat aorta, heart and brain.Those results indicate that, at micromolar concentrations, thapsigargin inhibits the voltage-dependent Ca²⁺ current by a direct interaction with the L-type Ca²⁺ channels.On leave from the A. A. Bogomoletz Institute of Physiology, Kiev, Ukraine     

(−)-Epigallocatechin-3-gallate induces contraction of the rat aorta by a calcium influx-dependent mechanism

Although the consumption of tea has been associated with beneficial cardiovascular effects, (–)-epigallocatechin-3-gallate (EGCG), the most abundant catechin in this beverage has shown seemingly contradictory actions on vascular tissues, for example vasorelaxant activity that could contribute favourably to prevention of cardiovascular disease, and contractile activity that could act in the opposite direction. The purpose of the present work was to study the contractile effects of EGCG on isolated rat thoracic aorta rings and its effects on the cytosolic free [Ca²⁺] ([Ca²⁺]_i) measured with fura-2 in cultured rat aortic smooth muscle cell line.In partially depolarised (15 mM KCl) aortic rings EGCG (30–300 µM), (±)-BAY K 8644 (0.1 µM) and thapsigargin (1 µM) induced a Ca²⁺-dependent, endothelium-independent contraction associated with [Ca²⁺]_i elevation in RASMC. EGCG enhanced the responses elicited by (±)-BAY K 8644 and thapsigargin both in aortic rings and in RASMC. Nifedipine totally inhibited the (±)-BAY K 8644-induced contraction, but only partially blocked the contractile responses to EGCG and thapsigargin, while SKF 96365 abolished both responses. The effects of these channel blockers were associated with a decrease in [Ca²⁺]_i in RASMC. Re-introduction of Ca²⁺ in the medium after depletion of intracellular Ca²⁺ stores with thapsigargin in a Ca²⁺-free solution elicited a contraction of aortic rings and an increase in [Ca²⁺]_i in RASMC. In both cases, this response was partially sensitive to nifedipine, abolished by SKF 96365 and clearly enhanced by EGCG.These results suggest that EGCG induces a transient endothelium-independent contraction in the rat aorta, probably by increasing smooth vascular cell membrane permeability to Ca²⁺ through both non-specific and dihydropyridine-sensitive Ca²⁺ channels.     

Characteristics of palytoxin-induced cation currents and Ca2+ mobilization in smooth muscle cells of rabbit portal vein

We examined the nature of the palytoxin (PTX)-induced channel and its relevance to the Ca²⁺ mobilizing effect of the toxin on smooth muscle cells isolated from rabbit portal vein using whole-cell voltage-clamp and microfluorimetric techniques. PTX (1 nM) induced a sustained, irreversible inward current at a holding potential of –40 mV. The PTX-induced current reversed at 0.5 ± 0.6 mV, and the PTX-induced channel permitted the passage of Na⁺, K⁺, Cs⁺ and, to a lesser extent, Li⁺, but not choline⁺ or Ca²⁺. During the sustained phase of the current, superfusion of Ni²⁺ (5 mM), La³⁺ (0.5 mM) or 2,4-dichlorobenzamil (2,4-DCB, 25 μM) reduced the current amplitude and decreased the slope conductance without changing the reversal potential. In 5 of 7 experiments, ouabain transiently increased the PTX-induced inward current and shifted the reversal potential in a positive direction. Subsequently, ouabain inhibited the current in every cell. PTX (10 nM) induced a sustained rise in cytosolic Ca²⁺ ([Ca²⁺]_i), which was resistant to verapamil but suppressed by omission of extracellular Ca²⁺. When external Na⁺ was replaced by choline⁺, PTX did not increase [Ca²⁺]_i. Pretreatment with 2,4-DCB prevented the elevation of [Ca²⁺]_i due to PTX. These results suggest that PTX does not directly stimulate Ca²⁺ entry but induces entry through Na⁺-Ca²⁺ exchange as a consequence of increased cytosolic Na⁺. Ni²⁺, La³⁺, 2,4-DCB and ouabain were shown to act as blockers of the PTX-induced channel. Ouabain may also inhibit Na⁺ pump current activated by cytosolic Na⁺. Received: 15 May 1996 / Accepted: 28 August 1996     

Reduction in extracellular Ca^2＋ attenuates endothelium-dependent relaxation more than nitroprussideinduced relaxation

Aim:

To quantitatively assess the effect of lowering external Ca²⁺ ([Ca²⁺]_o) on both endothelium-dependent and -independent relaxations in rabbit aorta.

Methods:

Isometric contractions and relaxations of isolated aortae were recorded. When assessing the effect of reduced [Ca²⁺]_o on relaxations, the normal [Ca²⁺]_o solution was substituted with one of the reduced [Ca²⁺]_o solutions for one aorta, while a paired aorta was replenished with normal [Ca²⁺]_o solution.

Results:

The extent of acetylcholine (ACh)-induced relaxation, which is dependent on an intact endothelium, is time-dependent, and inversely related to [Ca²⁺]_o in a range of 0.02–2 mmol/L. ACh-induced relaxations were not significantly altered by the magnitude of the precontraction induced by PGF_2α. Nitroprusside-induced relaxations, which are independent of the endothelium, are also attenuated by reduced [Ca²⁺]_o. Relaxant responses to ACh were significantly more susceptible to reduced [Ca²⁺]_o than nitroprusside-induced relaxations. A maximally effective relaxing concentration of D600, an L-type Ca channel blocker methoxyverapamil, (10⁻⁵ mol/L) attenuated ACh-induced relaxations, whereas nitroprusside-induced relaxations were unaffected by D600.

Conclusion:

Thus, endothelium-dependent relaxation is more dependent on [Ca²⁺]_o than endothelium-independent relaxation, and it seems likely that [Ca²⁺]_o plays an important role not only in contractile processes, but also in relaxant processes as well.     

Characterization of two different Ca2+ entry pathways dependent on depletion of internal Ca2+ pools in rat aorta

Ryanodine (10 μM), thapsigargin (1 μM) and cyclopiazonic acid (10 μM) produced a slow, sustained contractile response in rat aorta that only can be observed in Ca²⁺-containing solution. In Ca²⁺-free medium, no response to the drugs was obtained, which suggests that the contraction elicited in presence of Ca²⁺ is mainly due to the contribution of extracellular influx. This Ca²⁺ entry does not depend on the opening of dihydropyridine-dependent Ca²⁺-channels for nimodipine does not affect this. Noradrenaline (1 μM) induced a biphasic response in Ca²⁺-free medium that was mediated by two different Ca²⁺ compartments, one of which is common to caffeine (10 mM), and is also depleted by ryanodine (10 μM), thapsigargin (1 μM) and cyclopiazonic acid (10 μM). This compartment loses its Ca²⁺ content after long exposure (65 min) to Ca²⁺-free EDTA-containing solution and its refilling was also affected by the three agents tested. The other compartment depleted by noradrenaline, but not by caffeine, was also insensitive to ryanodine, thapsigargin and cyclopiazonic acid, and did not lose its Ca²⁺ after 65 min in Ca²⁺-free medium. Contractions induced by noradrenaline (1 μM) or caffeine (10 mM) in Ca²⁺-free medium were not affected by ryanodine, thapsigargin and cyclopiazonic acid when these agents were added 1 min before or during the response to each agonist. After depletion of internal Ca²⁺ stores sensitive to noradrenaline, an increase in the resting tone (IRT) of rat aorta was observed when Ca²⁺ was added again in absence of the agonist. This IRT was not affected by treatment with ryanodine, thapsigargin and cyclopiazonic acid, and represents a Ca²⁺ entry pathway dependent on the depletion of the noradrenaline-sensitive Ca²⁺ compartment. In conclusion, we can differentiate two Ca²⁺ entry pathways in rat aorta that depend on the previous depletion of two internal Ca²⁺ compartments: One corresponds to the classic capacitative Ca²⁺ entry model and is promoted by depletion of the internal pool sensitive to noradreanline, caffeine, ryanodine, thapsigargin and cyclopiazonic acid, the other is dependent only on depletion of an α₁-adrenoceptor-sensitive Ca²⁺ pool. Received: 25 June 1997 / Accepted: 17 September 1997     

吉非罗齐拮抗Bay K 8644增加大鼠主动脉平滑肌细胞L-型电压依赖性钙电流

目的 观察吉非罗齐拮抗Bay K 8644对离体大鼠主动脉的收缩效果,并进一步研究其机制。方法 采用离体血管张力记录法记录大鼠主动脉血管环的张力变化,膜片钳电生理学记录大鼠主动脉平滑肌细胞L-型电压依赖性钙电流。结果 Bay K 8644可以引起大鼠主动脉血管环收缩,最大收缩幅度为(2.13±0.42)g,提前孵育吉非罗齐可以对Bay K 8644的收缩幅度起到一定程度的抑制作用,使其收缩幅度降至(1.02±0.36)g。提前孵育L-NAME和去内皮均没有对吉非罗齐的抑制效果产生明显影响。Bay K 8644可以使得大鼠主动脉平滑肌细胞L-型钙电流增大127.62%,而吉非罗齐的干预,可以使其增幅降低到79.48%。结论 吉非罗齐可以一定程度上抑制Bay K 8644引起的大鼠主动脉收缩,其效果不受一氧化氮合酶抑制剂L-NAME及去内皮的影响。吉非罗齐可以部分拮抗Bay K 8644引起的大鼠离体主动脉平滑肌细胞L-型电压依赖性钙电流的增大。     

On the mechanism of action of phenylephrine in rat atrial heart muscle

Both in rat left atrial heart and in aortic smooth muscle preparations, phenylephrine (PE) caused a concentration-dependent increase in force of contraction (F_c) in the presence of atenolol (10 mol/l), which was antagonized by phentolamine, prazosin and WB 4101 in a competitive manner. The pA₂ values of the antagonists in the cardiac tissue were 10–20fold lower than those in the rat thoracic aorta. In the spontaneously beating right atrium, PE exerted a positive chronotropic action, which was not significantly antagonized by phentolamine or prazosin. It is therefore assumed that the effects of phenylephrine in the left atrium and in the aorta are mediated by different subtypes of ₁-adrenoceptors, whereas the effects in the sino-atrial node are probably unrelated to ₁-adrenoceptors. To further elucidate the mechanisms of the positive inotropic effect of PE, action potential configuration and ⁴⁵Ca²⁺ fluxes were monitored in the rat left atrium. The increase in F_c by PE was associated with an increase in action potential duration (APD) and a reduction in resting membrane potential (RP). In the presence of (–)-devapamil (13888), the effects of PE on APD and RP persisted, whereas the increase in F_c was antagonized in a non-competitive manner. Forskolin (300 nmol/l) enhanced the positive inotropic effect of PE. PE exerted a significant increase in ⁴⁵CA²⁺ uptake in beating preparations, which was abolished in the presence of (–)13888 (1 mol/l). In addition to the PE-induced increase in ⁴⁵Ca²⁺ uptake, a decrease in ⁴⁵Ca²⁺ efflux was observed. Similarly, depolarization of the membrane by raising [K⁺]_o to 85 mmol/l revealed an increase in ⁴⁵Ca²⁺ uptake and a decrease in ⁴⁵Ca²⁺ efflux. The latter observations support the view that the membrane potential strongly determines the movement of ⁴⁵Ca²⁺ across the membrane. It is assumed that the ₁-adrenoceptor-mediated changes in APD and RP may enhance F_c, first, by increasing net Ca²⁺ entry from the extracellular space through voltage-dependent Ca²⁺ channels and, second, by decreasing Ca²⁺ efflux possibly via the Na ⁺/Ca²⁺ exchange mechanism.     

四肽FMRFa对大鼠心室肌Na+/Ca2+交换的抑制

目的　研究四肽FMRFa对大鼠单个心室肌细胞Na⁺/Ca²⁺交换的作用。方法　用膜片钳全细胞记录法测定成年大鼠心室肌细胞Na⁺/Ca²⁺交换电流(I_Na⁺/Ca²⁺)和其他离子通道电流。结果　FMRFa对大鼠心室肌细胞I_Na⁺/Ca²⁺呈浓度依赖性抑制,100μmol·L^-1浓度时抑制内向和外向I_Na⁺/Ca²⁺密度分别达60.1%和56.5%,对内向电流及外向电流的IC₅₀分别为20μmol·L^-1和34μmol·L^-1。FMRFa5μmol·L^-1抑制I_Na⁺/Ca²⁺内向和外向电流密度分别为38.7%和34.9%,但FMRFa5μmol·L^-1及20μmol·L^-1对L型钙电流、钠电流、瞬时外向电流和内向整流钾电流均无显著抑制作用。结论　FMRFa对大鼠心室肌细胞是一个特异性Na⁺/Ca²⁺交换抑制剂。     

Contraction of the sheep middle cerebral,pulmonary and coronary arteries initiated by release of intracellular calcium

1 The aim of the study was to compare contraction initiated by intracellular Ca²⁺ release in the middle cerebral, coronary and pulmonary arteries of the sheep. With all three arteries from the sheep, incubation in Ca²⁺-free physiological salt solution (PSS) reduced agonist-induced contraction much more than occurred with the rabbit aorta. The intracellular Ca²⁺ store appeared to be of limited capacity, since contraction was transient in Ca²⁺-free conditions with most agonists. 2 In the middle cerebral artery, contraction in Ca²⁺-free conditions was much reduced if a previous contraction had been obtained (for 5-hydroxytryptamine, 5-HT, from 11 + 4 to 1 + 0.5% of control contraction in 2.5 mm Ca²⁺), suggesting that the previous contraction had partly discharged the intracellular Ca²⁺ store. Contraction was less affected in the pulmonary artery and almost unaffected in the coronary artery (for 5-HT, from 15 + 1 to 11 + 1%) by a previous contraction in Ca²⁺-free conditions. 3 Rings prepared from small branches of the pulmonary and coronary arteries were affected by Ca²⁺ deprivation in a similar manner to large diameter pulmonary and coronary artery rings. 4 In Ca²⁺-free PSS, contraction induced by prostaglandin E₂ was almost eliminated (3 + 1% of control contraction in 2.5 mm Ca²⁺), contractions induced by 5-HT and noradrenaline were reduced, and contraction induced by the thromboxane mimetic U46619 was least affected (up to 73 + 8%). 5 Increasing agonist concentration from EC₅₀ to the maximally effective concentration raised the percentage contraction remaining in the middle cerebral artery (for noradrenaline from 7 + 2% to 12 + 3%) but not in the pulmonary artery (for noradrenaline from 22 + 2% to 24 + 6%). 6 The present study has revealed notable differences, in coupling to intracellular Ca²⁺ release between the three vascular territories studied.     

阿托品对兔胸主动脉平滑肌收缩和细胞增殖的影响

用兔胸主动脉条研究Atr,Ver对CaCl₂,Atr对KCI量—效反应的影响。观察到Atr和Ver能抑制2种激动剂所致兔主动脉条的收缩,量一效曲线右移,最大反应降低,其pD₂值分别为4.4和5.8。两药也能明显抑制NE依内Ca²⁺性收缩,Atr对NE依外Ca²⁺性收缩影响较小,说明Atr主要对细胞外Ca²⁺经PDC所致的收缩有抑制作用。在兔ASMC培养中,有Ca²⁺时,Atr抑制ASMC增殖,无Ca²⁺时,Atr 20.6～185.2 μmol/L表现刺激增殖,555.7～1666.7 μmol/L则抑制MSMC增殖,说明Atr对ASMC作用也与Ca(2+)有关。     

Studien zur Chemie von thienoanellierten O,N- und S,N-haltigen Heterocyclen, 9. Mitt.: Synthese und Calciumkanal blockierende Wirkung eines thienoanalogen KT-362

Synthesis and Ca²⁺Antagonistic Activity of a Thieno-KT-362 Analogue The thienoanalog of the calcium antagonist KT-362, compound 3 , was prepared from ester 5 and the Ca²⁺ antagonistic activity was evaluated in isolated ring segments of rat aorta.