Differential effect of calcium and Bay K 8644 on the inhibitory action of estrogens in the rat uterus.

1. The effects of the estrogens estradiol (E2, 10(-7) to 3 x 10(-5) M) and diethylstilbestrol (DES, 10(-7) to 3 x 10(-6) M) on tonic contractions of the rat uterus induced by KCl and CaCl2 have been studied. 2. E2 and DES relaxed, in a dose-dependent way, the tonic contraction induced by KCl (60 mM) (IC50: 5.16 +/- 1.49 x 10(-6) and 4.51 +/- 0.03 x 10(-7) M); the tonic contraction induced by CaCl2 (3 mM) in the rat uterus incubated in depolarizing Krebs (127 mM of K+) have also been relaxed (IC50: 8.6 +/- 0.03 x 10(-7) and 2.56 +/- 0.07 x 10 M) by both drugs. 3. The CaCl2 (0.1 to 10 mM) counteracted the relaxing effect of E2 and DES, respectively, up to 28.13 +/- 10.2% and 34.71 +/- 11.5%, on KCl-induced contractions, and up to 126.36 +/- 19.35% and 95.8 +/- 16.3% on CaCl2-induced contractions. 4. Bay K 8644 (10(-10) to 10(-6) M) reversed the relaxing effect of E2 and DES, respectively, up to 42.49 +/- 2.28% and 43.31 +/- 3.59% on KCl-induced contractions, and up to 21.73 +/- 4.16% and 75.97 +/- 9.63% on CaCl2-induced contractions. 5. Propranolol (10(-6) M) did not modify the relaxing effect of E2 or DES on CaCl2-induced contractions.     

Antagonism of Ca2+ and other actions of verapamil in guinea-pig isolated trachealis.

In trachealis bathed by a K+-rich, Ca2+-free physiological salt solution, calcium chloride (CaCl2) at 0.01 to 10 mmol l-1 evoked concentration-dependent spasm. Verapamil (0.1 to 10 mumol l-1) was an effective antagonist of CaCl2. Spasm evoked by acetylcholine, histamine, potassium chloride (KCl) and tetraethylammonium (TEA) was studied in trachealis bathed by normal Krebs solution. Verapamil (0.1 to 10 mumol l-1) markedly suppressed spasm evoked by KCl and TEA. In contrast the actions of acetylcholine and histamine were much less affected by verapamil. Spasm evoked by prostaglandin E2 was studied in trachealis bathed by Krebs solution containing indomethacin (2.8 mumol l-1). Verapamil (0.1 to 10 mumol l-1) had little or no effect against prostaglandin E2-induced spasm. Verapamil (0.1 to 10 mumol l-1) had relatively little effect on the tone of trachealis bathed by normal Krebs solution. In contrast bathing in Krebs solution lacking CaCl2 caused almost complete tone loss. Extracellular electrophysiological recording showed that verapamil (10 mumol l-1) suppressed not only TEA-evoked spasm but also TEA-evoked slow waves and spike potentials. Verapamil also abolished the transient period of slow wave activity associated with the spasm evoked by KCl. Intracellular electrophysiological recording showed that TEA-induced spike activity was resistant to tetrodotoxin (3 mumol l-1). However, verapamil (10 mumol l-1) abolished the tetrodotoxin-resistant spikes without increasing the resting membrane potential. It is concluded that verapamil suppresses TEA- or KCl-induced spasm, slow waves or spikes by inhibition of Ca2+ influx.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lack of effect of leukotriene D4 on Ca-uptake in airway smooth muscle.

The effects of verapamil on leukotriene D4 (LTD4)- and KCl-induced contractions and 45Ca-uptake were examined in guinea-pig isolated tracheal smooth muscle. Both LTD4 (0.1 to 200 nmol l-1) and KCl (8 to 125 mmol l-1) produced concentration-dependent increases in tension in the tracheal preparations. Verapamil (1 mumol l-1) inhibited the tension responses induced by both LTD4 and KCl. LTD4 failed to increase the lanthanum-resistant Ca content of tracheal smooth muscle at either low (EC25; 3 nmol l-1) or high (EC90; 50 nmol l-1) concentrations. Verapamil did not modify this result. KCl (90 mmol l-1) increased the lanthanum-resistant Ca content of the smooth muscle by approximately 60% over basal levels. This effect was completely inhibited by verapamil (1 mumol l-1). It is concluded that in this tissue, LTD4 utilizes principally an intracellular source of Ca2+ to initiate contraction whereas KCl is dependent upon the uptake of Ca2+ from the extracellular compartment. It is suggested that the inhibitory effects of verapamil may reflect an intracellular mechanism of action directed against Ca2+ release initiated by LTD4.     

INFLUENCE OF MANGANESE IONS ON THE CONTRACTION OF THE GUINEA-PIG ISOLATED VAS DEFERENS

1. The CaCl2-induced contraction of guinea-pig isolated vas deferens, pretreated with tetrasodium edetate and then transferred to edetate-free sucrose medium, was increased in the presence of MnCl2 in extremely low concentrations (0.005-0.01 mmol/l) but was suppressed by the salt in concentrations higher than 1.0 mmol/l. 2. The KCl-induced contraction of the preparation, kept in a sucrose medium without edetate-pretreatment, was suppressed by MnCl2 (0.005-0.5 mmol/l) in a concentration-dependent manner. 3. The noradrenaline-induced contraction of the preparation kept in Locke's solution, was not influenced by MnCl2 in concentrations lower tha 0.1 mmol/l but was inhibited by higher concentrations (0.1-1.0 mmol/l).     

Effects of m-nisoldipine on anoxia-potentiated histamine and acetylcholine-induced contractions of the porcine isolated coronary artery

Anoxia (95% N2 + 5% CO2) potentiated the contractile response to KCl 20 mmol/L, histamine (His) 5 mumol/L and acetylcholine (ACh) 0.5 mumol/L in isolated porcine coronary arterial rings. Calcium antagonists m-nisoldipine (m-Nis) and nisoldipine (Nis) 0.4-250 nmol/L produced a concentration-dependent decrease in both KCl, His and anoxia-potentiated KCl2 His or ACh-induced contractions. Chlorpheniramine 10 mumol/L but not cimetidine 10 mumol/L and atropine 10 mumol/L abolished contractions induced by His and ACh respectively. All 3 agents did not affect KCl response and the anoxia facilitation. Indomethacin 10 mumol/L markedly attenuated the further increase in tension by anoxia but failed to inhibit the response by these vasoconstrictors.     

Muscarinic regulation of somatostatin release from primary cultures of human antral epithelial cells.

A newly developed, primary culture of human antral epithelial cells has been utilized to examine the effect of parasympathomimetics on somatostatin release. The cholinergic agonists, carbachol and methacholine, stimulated somatostatin secretion in a concentration-dependent manner. Maximal release in response to carbachol was observed at 0.1 mmol/l. Methacholine was 10 times more potent with a significant release being observed at 1 mumol/l, maximal secretion was observed at 10 mumol/l. Somatostatin release, stimulated by the mixed nicotinic and muscarinic agonist, carbachol, was attenuated by the addition of atropine at 0.1 mumol/l but was unaffected by the same concentration of pirenzepine. Methacholine-stimulated release was attenuated by addition of 0.1 mumol/l atropine and unaffected by the same concentration of pirenzepine. The response to methacholine was reversed by the addition of 0.1 mumol/l 4-diphenylacetoxy-n-methylpiperidine methiodide (4-DAMP) and attenuated by 1 nmol/l 4-DAMP indicating that the effect was mediated by an M3 receptor. In conclusion, human antral D cells are stimulated by parasympathomimetics acting at an M3 receptor.     

Effects of calcium antagonists on rat normal and skinned fundus.

Calcium chloride (CaCl2) (0.1-25 mM, in K(+)-depolarized tissue), KCl (10-112 mM) and acetylcholine (1 x 10(-9) M-1 mM) produced concentration-dependent contractions of rat isolated fundus. Verapamil (0.01-100 microM), cinnarizine (1-100 microM), trifluoperazine (10-500 microM) and dantrolene (50-250 microM) each produced a concentration-related rightward and downward shift of the log concentration-effect curve for CaCl2. The rank order of potencies of these antagonists, measured as the IC50 against Ca2+ (25 mM)-induced contraction of depolarized fundus, was verapamil (2.5 microM) greater than cinnarizine (8.7 microM) greater than trifluoperazine (85.1 microM) greater than dantrolene (greater than 250 microM). Cinnarizine (0.5 mM) and trifluoperazine (0.5 mM), but neither verapamil nor dantrolene depressed Ca2+ (20 microM)-evoked contraction of rat skinned fundus preparations. In intact preparations of rat fundus, verapamil had greater inhibitory effects on contractions produced by KCl than against those elicited by acetylcholine while trifluoperazine depressed to the same extent the responses to these two spasmogens. Dantrolene was without effect on contractions elicited by KCl or acetylcholine. Cinnarizine inhibited acetylcholine-induced responses but enhanced contractions to KCl. Augmentation of KCl-induced responses by cinnarizine is resistant to verapamil (1 microM). This enhancing effect of cinnarizine was not observed for KCl-induced contraction of guinea-pig fundus or rat gastro-oesophageal sphincter. In the rat fundus, cinnarizine (1-100 microM) produced an additional and concentration-related contraction when added on the plateau contraction to KCl (100 mM). The enhancing effect and the direct contraction produced by cinnarizine are at least partly dependent on extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

硫酸锌对离体血管平滑肌的作用

硫酸锌是体内一种重要的微量元素,它使离体动物心脏动作电位振幅降低,有效不应期延长,并能显著降低家兔窦房结自律性。本文采用离体豚鼠胸主动脉条和犬门静脉环标本,观察硫酸锌对KCl,CaCl_2和去甲肾上腺素(NE)诱发血管平滑肌收缩的影响。进一步探讨硫酸锌与Ca~(2 )的作用关系。     

甲基黄酮醇胺对离体豚鼠气管的作用

本文比较性研究甲基黄酮醇胺盐酸盐（ＭＦＡ），三氟拉嗪（Ｔｒｉ），维拉帕米（Ｖｅｒ），氨茶碱（Ａｍｉ）和异丙肾上腺素（Ｉｓｏ）对豚鼠离体气管的舒张作用．ＭＦＡ（０．１－０．３ｍｍｏｌ·Ｌ－１）时间依赖性舒张ＫＣｌ诱导的气管平滑肌收缩。低于０．１ｍｍｏｌ·Ｌ－１时ＭＦＡ对ＫＣｌ诱导的收缩仅有轻微作用，却使Ｉｓｏ和Ａｍｉ的浓度舒张曲线明显向左上移动。ＭＦＡ，Ｖｅｒ，Ｔｒｉ使ＣａＣｌ２量效曲线向右下移，ｐＤ２值分别为：５．０±ｓ０．５，６．４±ｓ０．８，５．０±ｓ０．６．ＭＦＡ，Ｖｅｒ，Ｔｒｉ，Ａｍｉ剂量依赖性抑制次大量生理激动剂所致的收缩，其作用强度顺序为：Ｔｒｉ＞Ｖｅｒ＝ＭＦＡ＞Ａｍｉ．提示ＭＦＡ具有非竞争性钙拮抗作用，其作用方式与Ｔｒｉ相似。与Ａｍｉ相比、ＭＦＡ是一个较强的主气管扩张剂，并与Ａｍｉ，Ｉｓｏ具有明显的协同舒张支气管作用。     

Nonsteroidal antiestrogen inhibition of protein kinase C in human corpus luteum and placenta

These studies were undertaken to determine whether nonsteroidal antiestrogens would inhibit the calcium/lipid-dependent protein kinase (protein kinase C) activity in hormonally-responsive human reproductive tissues. Cytosol was prepared from human corpus luteum and term placenta. Protein kinase C activity was examined with various antiestrogens, estrogens, and catecholestrogens. The nonsteroidal antiestrogens tamoxifen, clomiphene and Z-4-hydroxytamoxifen inhibited protein kinase C in cytosol from human corpora lutea and placentae in a concentration-dependent manner. The IC50 values were 35-45 microM for tamoxifen, 58-66 microM for clomiphene, and 88 microM for hydroxytamoxifen. Protein kinase C purified 600-fold from human placenta was also inhibited by tamoxifen. The estrogens, estradiol and diethylstilbestrol (DES), and the catecholestrogens, 2-hydroxyestradiol and 4-hydroxyestradiol, had no effect on protein kinase C activity, nor were they able to prevent the inhibition of protein kinase C by the antiestrogens. Inhibition of the enzyme by the antiestrogens was competitive with phosphatidylserine and 1,2-diolein. In addition, tamoxifen inhibited enzyme activity stimulated by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). The data suggest that the action of these antiestrogens on protein kinase C was a direct inhibition of the enzyme. Furthermore, the site of interaction showed markedly different structural specificity from that of the estrogen receptor.     

Calcium channel blocking activity of calycosin, a major active component of Astragali Radix, on rat aorta

AIM: To investigate the vasoactivity of calycosin, a major active component of Astragali Radix. METHODS: Experiments were performed on isolated rat thoracic aortic rings pre-contracted with phenylephrine (PHE) or KCl. RESULTS: Calycosin produced a concentration-dependent relaxation on the tissue pre-contracted using PHE with 4.46+/-0.13 of pD(2) and 95.85%+/-2.67% of E(max); or using KCl with 4.27+/-0.05 of pD2 and 99.06%+/-2.15% of Emax, and displaced downwards the concentration-response curves of aortic rings to PHE or KCl. The relaxant effect of calycosin on denuded endothelium aortic rings was the same as on intact endothelium aortic rings, and its vasorelaxant effect was not influenced by L-NAME or indomethacin. In Ca(2+)-free solution, calycosin (30 micromol/L) did not have an effect on PHE (1 micromol/L)-induced aortic ring contraction. The effects of calycosin and nifedipine where somewhat different; calycosin decreased aortic ring contractions induced by the two agonists, but nifedipine displayed a more potent inhibitory effect on KCl-induced contractions than on PHE-induced contractions, and the vascular relaxing effects of calycosin and nifidipine were additive on PHE-induced contraction but not KCl-induced. CONCLUSION: Calycosin is a vasorelaxant. Its action is endothelium-independent and is unrelated to intracellular Ca(2+) release. It is a noncompetitive Ca(2+) channel blocker. The effect of calycosin on Ca(2+) channel blockade may be different from that of dihydropyridines. This study demonstrated a novel pharmacological activity of calycosin, and supplied a theoretic foundation for Astragali Radix application.     

Relaxant effect of trans-resveratrol on isolated porcine coronary arteries

Recent studies provided evidence that trans-resveratrol (3,4',5-trihydroxystilbene, found in high concentrations in some red wines, may possibly decrease the risk of coronary heart disease mortality. The aim of this study, performed with large epicardial porcine coronary arteries (PCA) strips, was to investigate the relaxant effect of trans-resveratrol on these main conductance vessels, which have been described to be pathologically prone for vasospastic contractions. The data show that the tonic component of the biphasic contractions induced by histamine, as well as the contractions induced by F- ions (10 mmol/l), which activate G proteins downstream of the receptors, could dose-dependently be inhibited by trans-resveratrol (0.1-100 mumol/l). The EC50 values of the dose-response curves established for the inhibition of the sustained component of histamine-induced contractions were very similar to those obtained for the relaxations of fluoride-induced contractions: 0.45 +/- 0.08 and 0.29 +/- 0.05 mumol/l, resp. (n = 6). Ouabain (10 mumol/l)-induced contractions and rhythmic contractions elicited by tetraethylammonium (12 mmol/l) were also strongly inhibited by trans-resveratrol (20 mumol/l). It may be inferred from the results obtained in this study, that the relaxation of the coronary conductance vessels induced by trans-resveratrol is possibly based on a nongenomic interaction with steroid-like receptors located on the cell membrane.     

Effects of the new potassium channel opener JTV-506 on coronary vessels in vitro and in vivo

The vascular effects of JTV-506 ((-)-(3S,4R)-2.2-bis(methoxymethyl)- 4-[(1,6-dihydro-l-methyl-6-oxo-3-pyridazinyl)amino]-3-hydroxychroman+ ++-6- carbonitrile hemihydrate, CAS 170148-29-5), a new potassium channel opener, was evaluated in isolated coronary arteries and anesthetized dogs. JTV-506 (1 nmol/l-3 mumol/l) produced a concentration-dependent relaxation in porcine isolated epicardial large coronary arteries precontracted with KCl (30 mmol/l), phenylephrine (3 mumol/l), histamine (3 mumol/l), serotonin (5-HT; 300 nmol/l), prostaglandin F2 alpha (PGF2 alpha; 10 mumol/l), U-46619 (100 nmol/l), endothelin-1 (ET-1; 30 nmol/l) and Bay K-8644 (100 nmol/l). JTV-506 was 2.5-8.5 and 13.3-81.5 times more potent than levcromakalim (CAS 94535-50-9) and nicorandil (CAS 65141-46-0), respectively, but was less potent than nifedipine (CAS 21829-25-4). JTV-506 and levcromakalim produced almost a complete relaxation in arteries precontracted with various kinds of vasoconstrictor, except for KCl. In contrast, nifedipine produced about 80-90% relaxation in arteries, precontracted with PGF2 alpha, U-46619 and ET-1. Thus, this potassium channel opener can be characterized as an agonist-nonselective vasorelaxant. The relaxing effects of JTV-506 and levcromakalim on coronary arteries precontracted with 30 mmol/l KCl was competitively antagonized by 3 mumol/l glibenclamide, an ATP-sensitive potassium (KATP) channel blocker. In canine isolated epicardial large coronary arteries, 10 mumol/l JTV-506, 10 mumol/l levcromakalim, 100 mumol/l nicorandil and 0.1 mumol/l nifedipine eliminated 10 mmol/l 3,4-diaminopyridine-induced rhythmic contractions. In anesthetized dogs, when administered directly into the coronary artery, JTV-506 induced dose-dependent increases in coronary arterial diameter and coronary blood flow. These results suggest that JTV-506 elicits coronary vasorelaxation through activation of the KATP channel. It is expected that JTV-506 might be useful in the treatment of coronary vasospasm in angina pectoris.     

Negative inotropic effect of 3,6-dimethamidodibenzopyriodonium citrate (I-65) on guinea pig papillary muscles

The effects of 3,6-dimethamidodibenzopyriodonium citrate (I-65) on the contractile response of electrically paced guinea pig papillary muscles in vitro were studied. I-65 (0.1-300 mumol/L) decreased the contractile force and inhibited isoprenaline-induced restoration of the contractile response in papillary muscles rendered inexcitable by KCl 22 mmol/L. Both effects were concentration-dependent, and the IC50 were 36.0 and 7.3 mumol/L, respectively. I-65 antagonized the positive inotropic effects of Iso and CaCl2 in a non-competitive manner. Like verapamil, I-65 had a frequency-dependent negative inotropic effect, and delayed the recovery of post-rest potentiation. It is concluded that the negative inotropic effect of I-65 results not only from the reduction of Ca2+-influx through the sarcolemmal membrane, but also from the inhibition of Ca2+ translocation in the sarcoplasmic reticulum.     

Airway smooth muscle relaxations induced by dipyrone

Background: Dipyrone differs from other nonsteroidal anti-inflammatory drugs with a distinctive spasmolytic effect; however, the mechanism of action is not clear yet. The possible mechanism behind this effect was investigated on airway smooth muscle tone in vitro. METHOD: The effect of dipyrone on inositol phosphate (IP) accumulation was evaluated on guinea pig trachea smooth muscle. Changes in intracellular free calcium levels and IP accumulation were evaluated in LTK8 cells. RESULTS: Dipyrone (0.01, 0.1, 1 mmol/l) had a relaxing effect on histamine (0.02 mmol/l)- and adenosine triphosphate- (ATP) (0.01 mol/l)-induced contractions, but not potassium chloride (KCl)-stimulated contractions. This relaxing effect was not observed with indomethacin. Indomethacin did not inhibit the relaxation response of dipyrone. In isolated tracheal smooth muscle, histamine- (0.02 mmol/l) and ATP (0.01 mmol/l)-induced IP accumulation was significantly inhibited by dipyrone (1 mmol/l). ATP (0.01 mmol/l)-induced IP accumulation was also significantly inhibited by dipyrone (0.01 mmol/l) in LTK8 cells. Dipyrone inhibited ATP-induced (0.01 and 0.1 mmol/l) intracellular calcium increase in LTK8 cells. CONCLUSION: Inhibition of the release of intracellular Ca(2+) may play a role in the smooth muscle relaxing effect of dipyrone. The inhibitor effect of dipyrone on IP accumulation may be due to direct inhibition of phospholipase C (PLC) or impairment of the activation of PLC by G protein-coupled receptor (GPCR).     

Effects of alaproclate, potassium channel blockers, and lidocaine on the release of 3H-acetylcholine from the guinea-pig ileum myenteric plexus

The guinea-pig ileum longitudinal muscle-myenteric plexus preparation, preincubated with 3H-choline or 3H-noradrenaline, was mounted in an organ bath and superfused with Tyrode's solution. Alaproclate (2-(4-chlorophenyl)-1,1-dimethyl 2-aminopropanoate) (0.01-0.5 mmol/l) reduced (IC50 = 0.1 mmol/l) and at about 0.5 mmol/l completely blocked the electrically evoked 3H-acetylcholine secretion. The depressing effect of alaproclate (0.2 mmol/l) was not counteracted by atropine (0.01, 1 or 10 mumol/l), hexamethonium (0.1 mmol/l), phentolamine (1 mumol/l) yohimbine (1 mumol/l), haloperidol (1 mumol/l), 8-phenyltheophylline (10 mumol/l), cyproheptadine (1 mumol/l), metitepine (1 mumol/l), bicuculline (10 mumol/l), picrotoxinin (0.1 mmol/l), forskolin (25 mumol/l), 3-isobutyl-1-methylxanthine (5 mmol/l), nifedipine (1 mumol/l), verapamil (1 mumol/l), dilitiazem (1 mumol/l), high calcium (6 mmol/l), high potassium (10 or 15 mmol/l), tetraethylammonium (2 mmol/l), 4-aminopyridine (0.5 mmol/l), apamin (0.5 mumol/l), barium (0.5 mmol/l) or quinine (0.1 mmol/l). Among the potassium channel blockers tested only quinine (at 0.5 or 1 mmol/l), in the same manner as lidocaine, reduced the evoked secretion of 3H-acetylcholine. The results are in agreement with the hypothesis that the effect of alaproclate on the evoked 3H-acetylcholine secretion is not mediated by a neurotransmitter receptor, or a potassium channel sensitive to tetraethylammonium, 4-aminopyridine, apamin, or barium or quinine, but is due to a local anaesthetic effect. In contrast to the evoked secretion, the spontaneous release of 3H-acetylcholine was enhanced by high concentrations of alaproclate (0.4-1 mmol/l). The mechanism underlying the effect of alaproclate on the spontaneous release remains to be established. Alaproclate (0.25 or 0.5 mmol/l) also enhanced the spontaneous release and reduced the electrically evoked 3H-noradrenaline secretion.     

Voltage-dependent effects of YC-170, a dihydropyridine calcium channel modulator,in cardiovascular tissues

Voltage-dependent effects of YC-170, a putative calcium channel activator, were examined and compared with those of Bay K 8644 in isolated guinea-pig cardiac tissues and rabbit aortae. In guinea-pig left atria superfused with a normal bathing solution (4 mmol/l K+), both YC-170 (10 mumol/l) and Bay K 8644 (1 mumol/l) produced a positive inotropic action accompanied by a prolongation of action potential durations (APDs). In normally-polarized guinea-pig papillary muscles Bay K 8644 increased force of contraction (fc) and APDs. However, YC-170 failed to increase fc in spite of a slight prolongation of APDs. In papillary muscles partially depolarized by 25 mmol/l K+ solution, Bay K 8644 enhanced the electrically-induced slow action potentials and contractile force. In contrast with Bay K 8644, YC-170 significantly depressed the slow action potentials and decreased fc. YC-170 also showed the depressant action on the slow action potentials induced by isoproterenol (0.1 mumol/l), histamine (3 mumol/l) and tetraethylammonium (10 mmol/l) plus high Ca2+ (4 mmol/l). In sinoatrial node cells of guinea-pig right atria Bay K 8644 produced a positive chronotropic action with increases in the maximum rate of rise (Vmax) and action potential amplitude (APA), whereas YC-170 produced a negative chronotropic action with decreases in Vmax and APA. In the rabbit aortic strips preincubated with bathing solution containing various concentrations of K+ (15, 20, 30 and 40 mmol/l), Bay K 8644 produced concentration-dependent contractions in a range of concentrations up to 0.3 mumol/l. However, when the concentration exceeded 1 mumol/l, Bay K 8644 caused a slight relaxation, irrespective of the K+ concentrations of bathing solution. YC-170 in concentrations of 10 and 30 mumol/l contracted the aortic strips placed in 5.9 or 15 mmol/l K+ bathing solution, but caused relaxation in 30 or 40 mmol/l K+ bathing solution. These results suggest that YC-170 is a dihydropyridine calcium channel modulator which behaves as a Ca2+ channel agonist in tissues of high membrane potentials, but as a Ca2+ channel antagonist in tissues of low membrane potentials.     

Gender-Specific Inhibition of Ca2+ Entry Mechanisms of Arterial Vasoconstriction by Sex Hormones

1. The clinical observation that hypertension is more common in males and postmenopausal women than in premenopausal women suggests vascular protective effects of female sex hormones, including hormone-mediated inhibition of vascular tone. The purpose of the present study was to investigate whether the Ca2+ mobilization mechanisms of vascular smooth muscle contraction are modified by gender and sex hormones. 2. Active stress and [45Ca2+] influx were measured in de-endothelialized aortic strips isolated from intact and gonadectomized male and female Sprague-Dawley rats. In normal Krebs' (2.5 mmol/L Ca2+), both phenylephrine (Phe; 10(-5) mol/L) and membrane depolarization by 96 mmol/L KCl increased active stress to 15.5 +/- 1.3 x 10(3) and 14.8 +/- 1.2 x 10(3) N/m2, respectively, and Ca2+ influx to 28.4 +/- 1.4 and 32.3 +/- 1.5 mumol/kg per min, respectively, in intact males. The Phe- and KCl-induced stress and Ca2+ influx were significantly reduced in intact females. Gonadectomy was associated with no significant changes in the Phe- and KCl-induced stress and Ca2+ influx in males, but was associated with significant enhancement in females. In Ca(2+)-free (2 mmol/L EGTA) Krebs', stimulation of intracellular Ca2+ release by Phe or caffeine (25 mmol/L) caused a transient contraction that was not significantly different in all groups of rats. 3. Exogenous application of 17 beta-oestradiol, progesterone or testosterone to aortic strips caused concentration-dependent inhibition of Phe- and KCl-stimulated contractions and Ca2+ influx. 17 beta-Oestradiol was the most effective hormone and its relative potency was intact males, castrated males and ovariectomized females > intact females. 4. Thus, vascular reactivity and Ca2+ entry in aortic smooth muscle are reduced in the presence and enhanced in the absence of female gonads. Both male and female sex hormones cause vascular relaxation, mainly by inhibiting Ca2+ entry, with oestrogen being the most effective, particularly in the absence of female gonads. The results suggest that a cellular mechanism of oestrogen-induced vascular relaxation involving inhibition of Ca2+ entry into vascular smooth muscle is gender dependent.     

Evidence for the mechanism of the inhibitory action of jatrophone in the isolated rat uterine muscle.

1. Jatrophone (JAT), a diterpene isolated from the plant Jatropha elliptica (1-300 microM), caused a concentration-dependent relaxation effect against acetylcholine (Ach)-oxytocin (Ot)- and KCl-induced uterine sustained contraction. The relative potency order was: Ach greater than Ot greater than KCl. 2. The relaxant effect of JAT was not modified by phorbol ester, forskolin, MIX, TMB-8 and W-7. The increase concentration of calcium (0.2-2 mM) in the medium did not reverse the inhibitory effect caused by JAT. 3. Pre-incubation of the preparations with JAT (16-32 microM) for 20 min, caused a concentration-dependent inhibition of KCl-induced contractile response. At 30 microM, JAT inhibited in an apparently non-competitive manner CaCl2-induced contraction in K+-depolarized preparations. High concentrations of JAT (100 microM) also caused a time-dependent relaxation in CaCl2-induced sustained uterine contraction (T1/2 = approx. 15 min). 4. JAT (30 microM) inhibited the dihydropyridine calcium channel agonist Bay K 8644-induced uterine contraction in an apparently non-competitive fashion, while verapamil (0.1 microM) caused an rightward displacement of Bay K 8644 contraction and marked inhibition of the maximal response.