Ionic mechanisms responsible for the antiarrhythmic action of dehydroevodiamine in guinea-pig isolated cardiomyocytes

Major Indole Alkaloids in Evodia Rutaecarpa: The Latest Insights and Review of Their Impact on Gastrointestinal Diseases

Evodia rutaecarpa, the near-ripe fruit of Euodia rutaecarpa (Juss.) Benth, Euodia rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang, or Euodia rutaecarpa (Juss.) Benth. var. bodinieri (Dode) Huang, is a famous herbal medicine with several biological activities and therapeutic values, which has been applied for abdominalgia, abdominal distension, vomiting, and diarrhea as a complementary and alternative therapy in clinic. Indole alkaloids, particularly evodiamine (EVO), rutaecarpine (RUT), and dedhydroevodiamine (DHE), are received rising attention as the major bioactivity compounds in Evodia rutaecarpa. Therefore, this review summarizes the physicochemical properties, pharmacological activities, pharmacokinetics, and therapeutic effects on gastrointestinal diseases of these three indole alkaloids with original literature collected by PubMed, Web of Science Core Collection, and CNKI up to June 2023. Despite sharing the same parent nucleus, EVO, RUT, and DHE have different structural and chemical properties, which result in different advantages of biological effects. In their wide range of pharmacological activities, the anti-migratory activity of RUT is less effective than that of EVO, and the neuroprotection of DHE is significant. Additionally, although DHE has a higher bioavailability, EVO and RUT display better permeabilities within blood-brain barrier. These three indole alkaloids can alleviate gastrointestinal inflammatory in particular, and EVO also has outstanding anti-cancer effect, although clinical trials are still required to further support their therapeutic potential.

The pharmacokinetics profiles, pharmacological properties, and toxicological risks of dehydroevodiamine: A review

Dehydroevodiamine (DHE) is a quinazoline alkaloid isolated from Evodiae Fructus (EF, Wuzhuyu in Chinese, Rutaceae family), a well-known traditional Chinese medicine (TCM) which is clinically applied to treat headache, abdominal pain, menstrual pain, abdominal distension, vomiting, acid regurgitation, etc. Modern research demonstrates that DHE is one of the main components of EF. In recent years, DHE has received extensive attention due to its various pharmacological activities. This review is the first to comprehensively summarize the current studies on pharmacokinetics profiles, pharmacological properties, and toxicological risks of DHE in diverse diseases. Pharmacokinetic studies have shown that DHE has a relatively good oral absorption effect in the mean concentration curves in rat plasma and high absorption in the gastrointestinal tract. In addition, distribution re-absorption and enterohepatic circulation may lead to multiple blood concentration peaks of DHE in rat plasma. DHE possesses a wide spectrum of pharmacological properties in the central nervous system, cardiovascular system, and digestive system. Moreover, DHE has anti-inflammatory effects via downregulating pro-inflammatory cytokines and inflammatory mediators. Given the favorable pharmacological activity, DHE is expected to be a potential drug candidate for the treatment of Alzheimer's disease, chronic stress, amnesia, chronic atrophic gastritis, gastric ulcers, and rheumatoid arthritis. In addition, toxicity studies have suggested that DHE has proarrhythmic effects and can impair bile acid homeostasis without causing hepatotoxicity. However, further rigorous and well-designed studies are needed to elucidate the pharmacokinetics, pharmacological effects, potential biological mechanisms, and toxicity of DHE.

Therapeutic effects and potential mechanism of dehydroevodiamine on N-methyl-N'-nitro-N-nitrosoguanidine-induced chronic atrophic gastritis

BACKGROUNDS

Dehydroevodiamine (DHE) is a quinazoline alkaloid isolated from a Chinese herbal medicine, named Euodiae Fructus (Wu-Zhu-Yu in Chinese). This study aimed to investigate the therapeutic effects and potential mechanism of DHE on N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced chronic atrophic gastritis (CAG) based on integrated approaches.

METHODS

Therapeutic effects of DHE on serum biochemical indices and histopathology of gastric tissue in MNNG-induced CAG rats were analyzed. MNNG-induced GES-1 human gastric epithelial cell injury model was established. Cell viability and proliferation was quantified by a cell counting kit-8 assay. Cell morphology and mitochondrial membrane potential (MMP) were detected by a high content screening (HCS) assay. Cell migration and invasion were detected by a Transwell chamber. Moreover, UHPLC-Q-TOF/MS was performed to investigate the potential metabolites and signaling pathway affecting the protective effects of DHE on MNNG-induced cell migration and invasion of GES-1. Furthermore, in view of the key role of angiogenesis in the transformation of inflammation and cancer, this study explored relative mRNA and protein expression levels of HIF-1α-mediated VEGF pathway in vivo and in vitro by RT-PCR and Western Blotting, respectively.

RESULTS

The results showed that the therapeutic effects of DHE on CAG rats were presented in down-regulation serum biochemical indices and alleviating histological damage of gastric tissue. Besides, DHE has an effect on increasing cell proliferation of GES-1 cells, ameliorating MNNG-induced gastric epithelial cell damage and mitochondrial dysfunction. In addition, DHE could inhibit MNNG induced migration and invasion of GES-1 cells. Cell metabolomics analyses showed that the protective effect of DHE on GES-1 cells is mainly associated with the regulation of inflammation metabolites and energy metabolism related pathways. It was found that DHE has a regulating effect on tumor angiogenesis and can inhibit the relative gene and protein expression of HIF-1α-mediated VEGF signaling pathway.

CONCLUSIONS

The present work highlighted the role of DHE ameliorated gastric injury in MNNG-induced CAG rats in vivo and GES-1 cell migration in vitro by inhibiting HIF-1α/VEGF angiogenesis pathway. These results suggest that DHE may be the effective components of Euodiae Fructus, which provides a new agent for the treatment of CAG.

A review on plants and herbal components with antiarrhythmic activities and their interaction with current cardiac drugs

This paper aimed to compile information on plants or their compounds which have experimentally shown antiarrhythmic effect and to scrutinize the efficacy and potency of them and their potential interaction with conventional cardiac drugs. Literature searches were accomplished by using numerous electronic databases, and the available knowledge on different parts of herbs and their ingredients with antiarrhythmic effects up to 2019 were identified and collected. The results indicate that 36 herbs or their derivatives can be effective in the treatment of arrhythmias, especially in animal and cellular models. They affect various ionic channels in different action potential phases. The alterations in ionic currents lead to changing in the amplitude and duration of the action potential, effective refractory period, maximum velocity, resting membrane potential, channel trafficking, or intracellular calcium concentration. The agents that prolong action potential duration and effective refractory period such as dauricine and sophocarpine seem to be more beneficial if more comprehensive studies confirm their efficacy and safety. It is noteworthy that the consumption of some herbal agents for cardiovascular (e.g. Hawthorn and Ginseng) or other (e.g. Ginseng and Licorice) therapeutic purposes may boost the pro-arrhythmogenic effect of current cardiovascular drugs such as cardiac glycosides. This study accentuates known plants or their derivatives with anti-arrhythmic effects, potential interaction with other cardiac drugs, and the possible mechanisms involved. It can assist clinicians and scientists in research and therapeutic approaches to the management of cardiac arrhythmias.

Dehydroevodiamine and hortiamine, alkaloids from the traditional Chinese herbal drug Evodia rutaecarpa, are IKr blockers with proarrhythmic effects in vitro and in vivo

Evodiae fructus is a widely used herbal drug in traditional Chinese medicine. Evodia extract was found to inhibit hERG channels. The aim of the current study was to identify hERG inhibitors in Evodia extract and to investigate their potential proarrhythmic effects. Dehydroevodiamine (DHE) and hortiamine were identified as I_Kr (rapid delayed rectifier current) inhibitors in Evodia extract by HPLC-microfractionation and subsequent patch clamp studies on human embryonic kidney cells. DHE and hortiamine inhibited I_Kr with IC₅₀s of 253.2±26.3nM and 144.8±35.1nM, respectively. In dog ventricular cardiomyocytes, DHE dose-dependently prolonged the action potential duration (APD). Early afterdepolarizations (EADs) were seen in 14, 67, 100, and 67% of cells after 0.01, 0.1, 1 and 10μM DHE, respectively. The proarrhythmic potential of DHE was evaluated in 8 anesthetized rabbits and in 8 chronic atrioventricular block (cAVB) dogs. In rabbits, DHE increased the QT interval significantly by 12±10% (0.05mg/kg/5min) and 60±26% (0.5mg/kg/5min), and induced Torsade de Pointes arrhythmias (TdP, 0.5mg/kg/5min) in 2 rabbits. In cAVB dogs, 0.33mg/kg/5min DHE increased QT duration by 48±10% (P<0.05*) and induced TdP in 2/4 dogs. A higher dose did not induce TdP. In human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), methanolic extracts of Evodia, DHE and hortiamine dose-dependently prolonged APD. At 3μM DHE and hortiamine induced EADs. hERG inhibition at submicromolar concentrations, APD prolongation and EADs in hiPSC-CMs and dose-dependent proarrhythmic effects of DHE at micromolar plasma concentrations in cAVB dogs should increase awareness regarding proarrhythmic effects of widely used Evodia extracts.

Implication of AMP-activated protein kinase in transient receptor potential vanilloid type 1-mediated activation of endothelial nitric oxide synthase

We investigated whether AMP-activated protein kinase (AMPK), a multifunctional regulator of energy homeostasis, is involved in transient receptor potential vanilloid type 1 (TRPV1)-mediated activation of endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs) and mice. In ECs, treatment with evodiamine, the activator of TRPV1, increased the phosphorylation of AMPK, acetyl-CoA carboxylase (ACC) and eNOS, as revealed by Western blot analysis. Inhibition of AMPK activation by compound C or dominant-negative AMPK mutant abrogated the evodiamine-induced increase in phosphorylation of AMPK and eNOS and NO bioavailability, as well as tube formation in ECs. Immunoprecipitation and two-hybrid analysis demonstrated that AMPK mediated the evodiamine-induced increase in the formation of a TRPVl-eNOS complex. Additionally, TRPV1 activation by evodiamine increased the phosphorylation of AMPK and eNOS in aortas of wild-type mice but did not activate eNOS in aortas of TRPV1-deficient mice. In mice, inhibition of AMPK activation by compound C markedly decreased evodiamine-evoked angiogenesis in matrigel plugs and in a hind-limb ischemia model. Moreover, evodiamine-induced phosphorylation of AMPK and eNOS in aortas of apolipoprotein E-deficient (ApoE^−/−) mice was abrogated in TRPVl-deficient ApoE^−/− mice. In conclusion, TRPV1 activation may trigger AMPK-dependent signaling, which leads to enhanced activation of AMPK and eNOS and retarded development of atherosclerosis.

Antiarrhythmic effects of dehydroevodiamine in isolated human myocardium and cardiomyocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Dehydroevodiamine alkaloid (DeHE), a bioactive component of the Chinese herbal medicine Wu-Chu-Yu (Evodiae frutus), exerted antiarrhythmic effect in guinea-pig ventricular myocytes. We further characterize the electromechanical effects of DeHE in the human atrial and ventricular tissues obtained from hearts of patients undergoing corrective cardiac surgery or heart transplantation.

MATERIALS AND METHODS

The transmembrane potentials of human myocardia were recorded with a traditional microelectrode technique while sarcolemmal Na(+) and Ca(2+) currents in single human cardiomyocytes were measured by a whole-cell patch-clamp technique. The intracellular pH (pHi) and Na(+)-H(+) exchanger (NHE) activity were determined using BCECF-fluorescence in human atria.

RESULTS

In human atria, DeHE (0.1-0.3 μM) depressed upstroke velocity, amplitude of action potential, and contractile force, both in slow and fast response action potential. Moreover, the similar depressant effects of DeHE were found in human ventricular myocardium. Both in isolated human atrial and ventricular myocytes, DeHE (0.1-1 μM) reversibly, concentration-dependently decreased the Na(+) and Ca(2+)currents. Moreover, DeHE (0.1 and 0.3 μM) suppressed delayed afterdepolarizations and aftercontractions, induced by epinephrine and high [Ca(2+)]o in atria. In human ventricular myocardium, the strophanthidin-induced triggered activities were attenuated by pretreating DeHE (0.3 μM). The resting pHi and NHE activity were also significantly increased by DeHE (0.1-0.3 μM).

CONCLUSIONS

We concluded for the first time that, in the human hearts, DeHE could antagonize triggered arrhythmias induced by cardiotonic agents through a general reduction of the Na(+) and Ca(2+) inward currents, while increase of resting pHi and NHE activity.

Gram-scale purification of dehydroevodiamine from Evodia rutaecarpa fruits, and a procedure for selective removal of quaternary indoloquinazoline alkaloids from Evodia extracts

Dehydroevodiamine (DHE) is a major bioactive constituent in the traditional Chinese herbal drug Evodiae fructus (Wu zhu yu). The compound has been shown to possess pronounced cardiovascular and neuropharmacological activities in vitro and in vivo. For quality control purposes and follow-up studies assessing potential safety risks of DHE, we developed a simple and efficient two-step protocol for gram-scale purification of DHE. An alkaloidal fraction was obtained by cation-exchange solid phase extraction, and DHE and the minor alkaloid hortiamine were purified by isocratic preparative RP-HPLC. The DHE content in different commercial batches of Evodiae fructus, and in a series of commercially available Evodia-containing TCM products was assessed. A daily intake of up to mg amounts of DHE was calculated from recommended doses of these products. A method for the selective removal of quaternary indoloquinazoline alkaloids from Evodia extracts was developed.

Activation of transient receptor potential vanilloid 1 decreases endothelial nitric oxide synthase phosphorylation at Thr497 by protein phosphatase 2B-dependent dephosphorylation of protein kinase C

AIMS

We investigated the effects and underlying molecular mechanism of transient receptor potential vanilloid 1 (TRPV1), a calcium (Ca(2+) )-permeable non-selective cation channel, on phosphorylation of endothelial nitric oxide synthase (eNOS) at threonine 497 (Thr497) in bovine aortic endothelial cells (BAECs) and in mice.

METHODS

Western blotting and immunoprecipitation were used for the evaluation of protein phosphorylation; protein phosphatase 2B (PP2B) activity was assessed by convention kit; Griess assay was for NO production; tube formation and Matrigel plug assay were used for angiogenesis.

RESULTS

In BAECs, treatment with the TRPV1 ligand evodiamine decreased the phosphorylation of eNOS at Thr497, protein kinase Cα (PKCα) at Serine 657 (Ser657) and PKCβ2 at Ser660. Evodiamine increased protein phosphatase 2B (PP2B) activity and promoted the formation of a PP2B-PKC complex. Inhibition of TRPV1 activation by the pharmacological antagonists, removal of extracellular Ca(2+) or pharmacological inhibition of PI3K/Akt/calmodulin-dependent protein kinase II/AMP-activated protein kinase signalling pathway abolished the evodiamine-induced alterations in phosphorylation of eNOS at Thr497, PKCα at Ser657, PKCβ2 at Ser660 and PP2B activity, as well as the formation of a PP2B-PKC complex. Inhibition of PP2B activation partially reduced the evodiamine-induced NO bioavailability and tube formation in endothelial cells (ECs) and angiogenesis in mice. Moreover, evodiamine decreased the phosphorylation of eNOS at Thr497, PKCα at Ser657 and PKCβ2 at Ser660 in apolipoprotein E (ApoE)-deficient mouse aortas but not TRPV1-deficient or ApoE/TRPV1 double-knockout mice.

CONCLUSION

TRPV1 activation in ECs may elicit a Ca(2+) -dependent effect on PP2B-PKC signalling, which leads to dephosphorylation of eNOS at Thr497 in ECs and in mice.

On the mechanisms of arrhythmias in the myocardium of mXinalpha-deficient murine left atrial-pulmonary veins

We have previously shown that left atrial-pulmonary vein tissue (LA-PV) can generate reentrant arrhythmias (atrial fibrillation, AF) in wild-type (mXinalpha+/+) but not in mXinalpha-null (mXinalpha-/-) mice. With the present experiments, we investigated the arrhythmogenic activity and the underlying mechanisms in mXinalpha+/+ vs. mXinalpha-/- LA-PV. Electrical activity and conduction velocity (CV) were recorded in LA-PV by means of a MED64 system. CV was significantly faster in mXinalpha+/+ than in mXinalpha-/- LA-PV and it was increased by 1 muM isoproterenol (ISO). AF could be induced by fast pacing in the mXinalpha+/+ but not in mXinalpha-/- LA-PV where automatic rhythms could occur. ISO increased the incidence of AF in Xinalpha+/+ whereas it increased that of automatic rhythms in mXinalpha-/- LA-PV. In LA-PV with the right atrium attached (RA-LA-PV), automatic rhythms occurred in all preparations. In mXinalpha+/+ RA-LA-PV simultaneously treated with ISO, strophanthidin and atropine, the incidence of the automatic rhythm was about the same, but AF increased significantly. In contrast, in mXinalpha-/- RA-LA-PV under the same condition, the automatic rhythm was markedly enhanced, but still no AF occurred. Conventional microelectrode techniques showed a longer APD(90) and a less negative maximum diastolic potential (MDP) in mXinalpha-/- than mXinalpha+/+ LA-PV tissues. Whole-cell current clamp experiments also showed a less negative MDP in mXinalpha-/- vs. mXinalpha+/+ LA-PV cardiomyocytes. The fact that AF could be induced by fast pacing under several conditions in mXinalpha+/+ but not in mXinalpha-/- LA-PV preparations appears to be due to a slower CV, a prolonged APD(90), a less negative MDP and possibly larger areas of conduction block in mXinalpha-/- myocardial cells. In contrast, the non-impairment of automatic and triggered rhythms in mXinalpha-/- preparations may be due to the fact that the mechanisms underlying these rhythms do not involve cell-to-cell conduction.

Oscillatory transient inward currents in ventricular myocytes of healthy versus myopathic Syrian hamster

The present experiments were performed in order to study abnormal action potential configuration and ion channel activity in ventricular myocytes obtained from 23 male myopathic Syrian hamsters (Biobreeders strain 14.6, 32-52 weeks old) compared with 10 age-matched healthy control hamsters (Biobreeders F1B) by means of whole-cell patch-clamp techniques. The results show that the myopathic myocytes had a longer action potential duration, a reduced transient outward K(+) current on depolarization and a smaller transient inward current on repolarization after prolonged depolarizing pulses (> 500 msec). However, the L-type Ca(2+) current and the inwardly rectifing K(+) current were not significantly different from those of healthy myocytes. The oscillatory transient inward currents could be diminished by treatment with ryanodine (0.01-1 micromol/L), a sarcoplasmic reticulum (SR) Ca(2+) release channel blocker, or with Na(+)-free superfusate. We conclude that the hereditary myopathic hamsters are less likely to develop delayed after depolarization-related transient inward currents and triggered arrhythmias owing to a smaller SR Ca(2+) content.

Calcium overload and cardiac function

The changes in cardiac function caused by calcium overload are reviewed. Intracellular Ca(2+) may increase in different structures [e.g. sarcoplasmic reticulum (SR), cytoplasm and mitochondria] to an excessive level which induces electrical and mechanical abnormalities in cardiac tissues. The electrical manifestations of Ca(2+) overload include arrhythmias caused by oscillatory (V(os)) and non-oscillatory (V(ex)) potentials. The mechanical manifestations include a decrease in force of contraction, contracture and aftercontractions. The underlying mechanisms involve a role of Na(+) in electrical abnormalities as a charge carrier in the Na(+)-Ca(2+) exchange and a role of Ca(2+) in mechanical toxicity. Ca(2+) overload may be induced by an increase in [Na(+)](i) through the inhibition of the Na(+)-K(+) pump (e.g. toxic concentrations of digitalis) or by an increase in Ca(2+) load (e.g. catecholamines). The Ca(2+) overload is enhanced by fast rates. Purkinje fibers are more susceptible to Ca(2+) overload than myocardial fibers, possibly because of their greater Na(+) load. If the SR is predominantly Ca(2+) overloaded, V(os) and fast discharge are induced through an oscillatory release of Ca(2+) in diastole from the SR; if the cytoplasm is Ca(2+) overloaded, the non-oscillatory V(ex) tail is induced at negative potentials. The decrease in contractile force by Ca(2+) overload appears to be associated with a decrease in high energy phosphates, since it is enhanced by metabolic inhibitors and reduced by metabolic substrates. The ionic currents I(os) and I(ex) underlie V(os) and V(ex), respectively, both being due to an electrogenic extrusion of Ca(2+) through the Na(+)-Ca(2+) exchange. I(os) is an oscillatory current due to an oscillatory release of Ca(2+) in early diastole from the Ca(2+)-overloaded SR, and I(ex) is a non-oscillatory current due to the extrusion of Ca(2+) from the Ca(2+)-overloaded cytoplasm. I(os) and I(ex) can be present singly or simultaneously. An increase in [Ca(2+)](i) appears to be involved in the short- and long-term compensatory mechanisms that tend to maintain cardiac output in physiological and pathological conditions. Eventually, [Ca(2+)](i) may increase to overload levels and contribute to cardiac failure. Experimental evidence suggests that clinical concentrations of digitalis increase force in Ca(2+)-overloaded cardiac cells by decreasing the inhibition of the Na(+)-K(+) pump by Ca(2+), thereby leading to a reduction in Ca(2+) overload and to an increase in force of contraction.

Effects of dehydroevodiamine exposure on glutamate release and uptake in the cultured cerebellar cells

Dehydroevodiamine has been reported to have neuroprotective and antiamnesic effects. This study examined the effects of dehydroevodiamine on glutamate release and uptake in cultured cerebellar cells. Chronic dehydroevodiamine exposure decreased the viability of granule cells. The basal and N-methyl-D-aspartate (NMDA)-induced release of glutamate from granule cells were decreased (26 and 14%) by dehydroevodiamine. The NMDA-induced release of glutamate was concentration-dependently inhibited in the granule cells. The basal and NMDA-induced releases of glutamate in chronically dehydroevodiamine-preexposed granule cells were unaffected by dehydroevodiamine. Glutamate uptake in the glial cells incubated without and with cAMP was inhibited (31% and 8%, respectively) by dehydroevodiamine. In the chronically dehydroevodiamine-preexposed glial cells, glutamate uptake was increased (8%) in the cAMP-coexposed glial cells by dehydroevodiamine but was unaffected in the naive cells. In addition, dehydroevodiamine potentiated (from 20% to 34%) the inhibition of L-pyrollidine-2,4-dicarboxylic acid (PDC) on glutamate uptake in naive glial cells, but this inhibition was reduced (from 41% to 26%) in cAMP-coexposed glial cells. These results suggest that dehydroevodiamine inhibits glutamate uptake and release. Furthermore, the results suggest that the characteristics of glutamate release and uptake in granule and glial cells may be altered by chronic exposure to dehydroevodiamine.

Effects of thyroid hormone on the arrhythmogenic activity of pulmonary vein cardiomyocytes

OBJECTIVES

This study was conducted to investigate the effects of thyroid hormone on the electrophysiological characteristics of pulmonary vein (PV) cardiomyocytes.

BACKGROUND

Hyperthyroidism is an important etiology of paroxysmal atrial fibrillation (AF). Pulmonary veins are known to initiate paroxysmal AF.

METHODS

The action potential and ionic currents were investigated in single rabbit PV and atrial cardiomyocytes with (hyperthyroid) and without (control) incubation of L-triiodothyronine using the whole-cell clamp technique.

RESULTS

Compared with the control cardiomyocytes, hyperthyroid PV and atrial cardiomyocytes had shorter action potential duration. Hyperthyroid PV cardiomyocytes had faster beating rates (1.82 +/- 0.13 Hz vs. 1.03 +/- 0.15 Hz, p < 0.005) and a higher incidence of delayed after depolarization (beating: 92% vs. 6%, p < 0.0001; non-beating: 45% vs. 3%, p < 0.005). However, only hyperthyroid PV beating cardiomyocytes had a higher incidence of early after depolarization (46% vs. 0%, p < 0.0001). The ionic current experiments showed that hyperthyroid PV beating cardiomyocytes had larger densities of overall slow inward (2.72 +/- 0.21 pA/pF vs. 2.07 +/- 0.19 pA/pF, p < 0.05), overall transient outward (1.39 +/- 0.21 pA/pF vs. 0.48 +/- 0.08 pA/pF, p < 0.001) and steady state outward currents (0.78 +/- 0.06 pA/pF vs. 0.58 +/- 0.04 pA/pF, p < 0.05) on depolarization and larger transient inward (0.021 +/- 0.004 pA/pF vs. 0.005 +/- 0.001 pA/pF, p < 0.001) on repolarization. By contrast, the hyperthyroid PV non-beating cardiomyocytes had larger densities of overall transient outward (1.01 +/- 0.14 pA/pF vs. 0.37 +/- 0.07 pA/pF, p < 0.001), steady state outward (0.61 +/- 0.06 pA/pF vs. 0.44 +/- 0.04 pA/pF, p < 0.05) and transient inward currents (0.011 +/- 0.002 pA/pF vs. 0.003 +/- 0.001 pA/pF, p < 0.05).

CONCLUSIONS

Thyroid hormone changes the electrophysiological activity of the PV cardiomyocytes. Increased automaticity and enhanced triggered activity may increase the arrhythmogenic activity of PVs in hyperthyroidism.

Effects of rapid atrial pacing on the arrhythmogenic activity of single cardiomyocytes from pulmonary veins: implication in initiation of atrial fibrillation

BACKGROUND

Pulmonary veins (PVs) are important sources of paroxysmal atrial fibrillation. Long-term rapid atrial pacing (RAP) changes atrial electrophysiology and facilitates the maintenance of atrial fibrillation. It is not clear whether RAP alters the arrhythmogenic activity of PVs. The purpose of this study was to isolate single PV cardiomyocytes from control and RAP dogs and evaluate their electrophysiological characteristics.

METHODS AND RESULTS

The action potential and ionic currents were investigated in PV cardiomyocytes from control and long-term (6 to 8 weeks) RAP (780 bpm) dogs by use of the whole-cell clamp technique. Dissociation of PVs yielded rod-shaped single cardiomyocytes without (n=91, 60%) or with (n=60, 40%) pacemaker activity. Compared with the control group, the RAP dog PV cardiomyocytes had faster beating rates (0.86+/-0.28 versus 0.45+/-0.07 Hz, P<0.05) and shorter action potential duration. The RAP dog PV cardiomyocytes with pacemaker activity have a higher incidence of delayed (59% versus 7%, P<0.001) or early (24% versus 0%, P<0.005) after depolarization. The RAP dog PV cardiomyocytes with pacemaker activity had smaller slow inward and transient outward but larger transient inward (0.017+/-0.004 versus 0.009+/-0.002 pA/pF, P<0.05) and pacemaker (0.111+/-0.019 versus 0.028+/-0.008 pA/pF, P<0.001) currents. The RAP dog PV cardiomyocytes without pacemaker activity had only smaller slow inward and transient outward and larger pacemaker currents.

CONCLUSIONS

PVs contain multiple cardiomyocytes with distinct electrophysiological characteristics. RAP changes the electrophysiological characteristics and arrhythmogenic activity of PVs.

Rutaecarpine-induced block of delayed rectifier K+ current in NG108-15 neuronal cells

The effects of rutaecarpine on ionic currents of NG108-15 neuronal cells were investigated in this study. Rutaecarpine (2-100 microM) suppressed the amplitude of delayed rectifier K+ current (I(K(DR))) in a concentration-dependent manner. The IC50 value for rutaecarpine-induced inhibition of I(K(DR)) was 11 microM. I(K(DR)) present in these cells is sensitive to the inhibition by quinidine and dendrotoxin, yet not by E-4031. The presence of rutaecarpine enhanced the rate and extent of I(K(DR)) inactivation, although it had no effect on the initial activation phase of I(K(DR)). Recovery from block by rutaecarpine (5 microM) was fitted by a single exponential with a value of 2.87 s. Crossover of tail currents in the presence of rutaecarpine was also observed. Cell-attached single-channel recordings revealed that rutaecarpine decreased channel activity, but it did not alter single-channel amplitude. With the aid of the binding scheme, a quantitative description of the rutaecarpine actions on I(K(DR)) was provided. However, rutaecarpine (20 microM) had no effect on L-type Ca2+ current. Under current-clamp configuration, rutaecarpine prolonged action potential duration in NG108-15 cells. These results show that rutaecarpine is a blocker of the K(DR) channel. The increase in action potential duration induced by rutaecarpine can be explained mainly by its blocking actions on I(K(DR)).

Dehydroevodiamine.HCl prevents impairment of learning and memory and neuronal loss in rat models of cognitive disturbance

We previously reported that dehydroevodiamine.HCl (DHED) has anticholinesterase and antiamnesic activities. To verify the effects of DHED on cognitive deficits further, we tested it on the scopolamine-induced amnesia model of the rat using the passive avoidance and eight-arm radial maze tests. A single (20 mg/kg p.o.) and repeated (10 mg/kg p.o.) administrations of DHED could significantly reverse the latency time shortened by scopolamine (1 mg/kg i.p.) to control level. The impaired spatial working memory induced by scopolamine (1 mg/kg i.p.) was also improved significantly by a single injection (6.25 mg/kg i.p.) and repeated administrations of DHED (10 mg/kg p.o.) in the eight-arm radial maze test. In addition, we examined the effects of DHED on the memory impairment and the histological changes of the brain after unilateral electrolytic lesion of the entorhinal cortex (EC) and middle cerebral artery occlusion in rats. The cognitive deficits caused by EC lesion and middle cerebral artery occlusion were improved significantly by repeated administrations of DHED (6.25 mg/kg i.p.) after EC lesion or ischemic insult once a day for 7 days in the passive avoidance test. Histological analysis showed that the neuronal loss in the DHED-treated group was notably reduced in the hippocampal area (CA1) of ischemic rats and in the dentate gyrus and hippocampal area (CA1 and CA3) of EC-lesioned rats compared with the nontreated group. The infarction area was decreased significantly by a single administration of DHED (6.25 mg/kg i.p.) 30 min before ischemic insult for 6 h. These results suggest that DHED might be an effective drug for not only the Alzheimer's disease type, but also the vascular type of dementia.

Reentrant tachyarrhythmias in right atria of cardiomyopathic versus healthy Syrian hamster

We studied the role of acetylcholine (ACh) and calcium overload in the induction of atrial flutter or atrial fibrillation (AF) in right atria from 34 normal male Syrian hamsters (F1B) and 33 cardiomyopathic Syrian hamsters (BIO 14.6) associated with focal myocardial necrosis. Action potential (AP) was recorded with conventional microelectrode techniques and twitch force by a transducer. ACh (0.1, 1 and 10 microM) induced high-frequency AF (around 33 Hz) along with tension oscillations and contracture in 7 of 12 normal hamster atria. These effects of ACh were abolished by tetrodotoxin or quinidine as well as by atropine. In contrast, ACh induced AF only in 1 of 12 myopathic atria. In both normal and myopathic atria, ACh induced similar changes in AP duration, spontaneous rate and force. The effects of calcium overload were tested by means of a high [Ca(2+)](o) (8.1 mM) low [K(+)](o) (1 mM) solution in another series of experiments. This solution also induced incidence of AF higher in normal (10/12) than in myopathic atria (4/12). The calcium load was also increased by high-frequency pacing (32 Hz for 3 or 30 s): AF occurred in normal atria (5/8), but not in myopathic atria (0/8). Measurement of the refractory period revealed a longer refractory period in myopathic than in control atria. We concluded that the lower incidence of AF in myopathic atria was probably due to their longer refractory period and the associated focal myocardial necrosis which then hindered the establishment of such a reentrant rhythm.

Mechanisms of vasorelaxant effect of dehydroevodiamine: a bioactive isoquinazolinocarboline alkaloid of plant origin

We examined the mechanisms underlying the vasorelaxant effect of dehydroevodiamine (DeHE), one of the bioactive components of the Chinese herbal drug Evodia rutaecarpa that has been shown to produce vasorelaxant and hypotension. DeHE (10(-7)-10(-4) M) concentration-dependently relaxed isolated rat mesenteric arteries precontracted with phenylephrine (PE). This vasorelaxant potency was diminished by 15% by endothelial removal, L-NG-nitro arginine, or methylene blue (MB), but not indomethacin treatment, indicating that the vasorelaxant effect of DeHE was partially endothelium dependent and mediated by nitric oxide (NO) and the cyclic GMP pathway. In endothelium-denuded preparations, DeHE caused a rightward shift of the contractile concentration-response curve (CRC) to PE in a dose-dependent manner with a pA2 value of 6.15. Maximal response was unaffected. Receptor binding assay indicated that DeHE competed with alpha 1-adrenoceptor ligand prazosin with a Ki value of 3.57 microM. Potassium channel activity-attenuating conditions such as increased level of extracellular K+ (20 mM) and treatment with the antagonist tetraethylammonium (TEA) significantly inhibited DeHE's effect, suggesting a mode of action similar to that of a potassium channel activator. In addition, high concentrations of DeHE (3 x 10(-5) and 10(-4) M) relaxed high K+ (80 mM)-evoked contraction, indicating that DeHE might possess K+ channel blocking properties. Multiple-action mechanisms, including endothelium dependence, alpha 1-adrenoceptor blockade, K+ channel activation, and Ca2+ channel blockade were probably involved in the vasorelaxant effects of DeHE.

Comparative study of the vasodilatory effects of three quinazoline alkaloids isolated from Evodia rutaecarpa

The vasoreactivity of dehydroevodiamine (1), evodiamine (2), and rutaecarpine (3), quinazoline alkaloids isolated from Evodia rutaecarpa, to aorta smooth muscle demonstrated that they produce a vasodilatory effect on endothelium-intact rat aorta with equal potency. Compound 3 produced a full (100%) nitric oxide-dependent vasodilatation, whereas 2 and 1 produced a partially endothelium-dependent effect, 50% and 10%, respectively. At the same time, I and 2 may also act by other mechanisms, including probably an alpha1-adrenoceptor blocking action and a 5-HT antagonizing action, respectively.

Depressant Effects of Prostacyclin in Human Atrial Fibers and Cardiomyocytes

The aim of this study was to characterize the electropharmacological effects of prostacyclin (PGI(2)) in human atrial fibers and cardiomyocytes. Atrial tissues obtained from the hearts of 28 patients undergoing corrective cardiac surgery were used. Transmembrane action potentials were recorded using a conventional microelectrode technique, and twitch force by a transducer. Effects of PGI(2) (1 nM-10 &mgr;M) on action potential characteristics and contraction of atrial fibers were evaluated in normal [K](o) (4 mM) and high [K](o) (27 mM) in the absence and presence of cardiotonic agents. In addition, atrial and ventricular myocytes were isolated enzymatically from atrial tissues and hearts of 4 patients undergoing cardiac transplant. The effects of PGI(2) on Na- and Ca-dependent inward currents (I(Na) and I(Ca)) of cardiomyocytes were tested. In 9 human atrial fibers showing fast-response action potentials (mean dV/dt(max) = 101 +/- 15 Vs(-1)) in 4 mM [K](o), PGI(2) did not influence dV/dt(max) of phase 0 depolarization even at 1 &mgr;M. However, at a concentration as low as 10 nM, PGI(2) depressed spontaneous rhythms or slow-response action potentials in high-K-depolarized fibers. PGI(2) also depressed delayed afterdepolarizations and aftercontractions induced by cardiotonic agents. In isolated cardiomyocytes, PGI(2) reduced I(Ca) but not I(Na). The present findings show that, in human atrial fibers and cardiomyocytes, PGI(2) induces greater depressant effects on the slow-response action potential, I(Ca) and triggered activity than on the fast-response action potential. It is suggested that PGI(2) may act through a selective reduction of transmembrane Ca influx. Copyright 1994 S. Karger AG, Basel

High-performance liquid chromatography of the quinazolinocarboline alkaloid dehydroevodiamine

A high-performance liquid chromatographic method has been developed for the determination of dehydroevodiamine (DeHE), an active principle from Evodia fruit. Plasma was denatured with acetonitrile and centrifuged, the supernatant was separated and blown dry, and the residue was redissolved in water. Bile was acidified with perchloric acid and centrifuged to yield the supernatant. Aliquots were used for analysis. Elution was isocratic on a reversed-phase column with acetonitrile-water-phosphoric acid (64:35:0.8, v/v) adjusted to pH 3.5 as the mobile phase. Ultraviolet detection was at a wavelength of 367 nm. The detection limits were 2 ng/ml for plasma and 10 ng/ml for bile. The intra-day and inter-day variations were mostly below 10%.