Effects of bepridil on early cardiac development of zebrafish

Bepridil is a commonly used medication for arrhythmia and heart failure. It primarily exerts hemodynamic effects by inhibiting Na⁺/K⁺ movement and regulating the Na⁺/Ca²⁺ exchange. In comparison to other Ca²⁺ inhibitors, bepridil has a long half-life and a complex pharmacology. Additionally, it is widely used in antiviral research and the treatment of various diseases. However, the toxicity of this compound and its other possible effects on embryonic development are unknown. In this study, we investigated the toxicity of bepridil on rat myocardial H9c2 cells. After treatment with bepridil, the cells became overloaded with Ca²⁺ and entered a state of cytoplasmic vacuolization and nuclear abnormality. Bepridil treatment resulted in several morphological abnormalities in zebrafish embryo models, including pericardium enlargement, yolk sac swelling, and growth stunting. The hemodynamic effects on fetal development resulted in abnormal cardiovascular circulation and myocardial weakness. After inhibiting the Ca²⁺ transmembrane, the liver of zebrafish larvae also displayed an ectopic and deficient spatial location. Additionally, the results of the RNA-seq analysis revealed the detailed gene expression profiles and metabolic responses to bepridil treatment in zebrafish embryonic development. Taken together, our study provides an important evaluation of antiarrhythmic agents for clinical use in prenatal heart patients.

Bepridil is potent against SARS-CoV-2 in vitro

Guided by a computational docking analysis, about 30 Food and Drug Administration/European Medicines Agency (FDA/EMA)-approved small-molecule medicines were characterized on their inhibition of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro). Of these small molecules tested, six displayed a concentration that inhibits response by 50% (IC50) value below 100 μM in inhibiting Mpro, and, importantly, three, that is, pimozide, ebastine, and bepridil, are basic molecules that potentiate dual functions by both raising endosomal pH to interfere with SARS-CoV-2 entry into the human cell host and inhibiting Mpro in infected cells. A live virus-based modified microneutralization assay revealed that bepridil possesses significant anti-SARS-CoV-2 activity in both Vero E6 and A459/ACE2 cells in a dose-dependent manner with low micromolar effective concentration, 50% (EC50) values. Therefore, the current study urges serious considerations of using bepridil in COVID-19 clinical tests.

Characterization of microminipig as a laboratory animal for pharmacological study by analyzing bepridil-induced cardiovascular responses

Since microminipig is becoming attractive model for various cardiac electropharmacological applications, which may meet consideration of 3Rs. We characterized microminipigs by analyzing how multi-ionic channel inhibitor bepridil may affect their in situ hearts in comparison with dogs. Bepridil in doses of 0.3 and 3.0 mg/kg were intravenously administered over 10 min under halothane anesthesia (n = 4). Microminipigs may be less sensitive for I_CaT inhibition of bepridil, whereas they are more responsive to I_Na, I_Kr and I_Ks suppression than dogs. This information would help predict cardiovascular effects of a drug in patients with the remodeled hearts having similar electrophysiological profile to microminipigs.

Identification of Novel Inhibitors of Auxin-Induced Ca2+ Signaling via a Plant-Based Chemical Screen

Many signal perception mechanisms are connected to Ca2+-based second messenger signaling to modulate specific cellular responses. The well-characterized plant hormone auxin elicits a very rapid Ca2+ signal. However, the cellular targets of auxin-induced Ca2+ are largely unknown. Here, we screened a biologically annotated chemical library for inhibitors of auxin-induced Ca2+ entry in plant cell suspensions to better understand the molecular mechanism of auxin-induced Ca2+ and to explore the physiological relevance of Ca2+ in auxin signal transduction. Using this approach, we defined a set of diverse, small molecules that interfere with auxin-induced Ca2+ entry. Based on annotated biological activities of the hit molecules, we found that auxin-induced Ca2+ signaling is, among others, highly sensitive to disruption of membrane proton gradients and the mammalian Ca2+ channel inhibitor bepridil. Whereas protonophores nonselectively inhibited auxin-induced and osmotic stress-induced Ca2+ signals, bepridil specifically inhibited auxin-induced Ca2+ We found evidence that bepridil severely alters vacuolar morphology and antagonized auxin-induced vacuolar remodeling. Further exploration of this plant-tailored collection of inhibitors will lead to a better understanding of auxin-induced Ca2+ entry and its relevance for auxin responses.

Reduced Aβ secretion by human neurons under conditions of strongly increased BACE activity

The initial step in the amyloidogenic cascade of amyloid precursor protein (APP) processing is catalyzed by beta-site APP-cleaving enzyme (BACE), and this protease has increased activities in affected areas of Alzheimer's disease brains. We hypothesized that altered APP processing, because of augmented BACE activity, would affect the actions of direct and indirect BACE inhibitors. We therefore compared post-mitotic human neurons (LUHMES) with their BACE-overexpressing counterparts (BLUHMES). Although β-cleavage of APP was strongly increased in BLUHMES, they produced less full-length and truncated amyloid beta (Aβ) than LUHMES. Moreover, low concentrations of BACE inhibitors decreased cellular BACE activity as expected, but increased Aβ_1-40 levels. Several other approaches to modulate BACE activity led to a similar, apparently paradoxical, behavior. For instance, reduction in intracellular acidification by bepridil increased Aβ production in parallel with decreased BACE activity. In contrast to BLUHMES, the respective control cells (LUHMES or BLUHMES with catalytically inactive BACE) showed conventional pharmacological responses. Other non-canonical neurochemical responses (so-called 'rebound effects') are well-documented for the Aβ pathway, especially for γ-secretase: a partial block of its activity leads to an increased Aβ secretion by some cell types. We therefore compared LUHMES and BLUHMES regarding rebound effects of γ-secretase inhibitors and found an Aβ rise in LUHMES but not in BLUHMES. Thus, different cellular factors are responsible for the γ-secretase- versus BACE-related Aβ rebound. We conclude that increased BACE activity, possibly accompanied by an altered cellular localization pattern, can dramatically influence Aβ generation in human neurons and affect pharmacological responses to secretase inhibitors. OPEN PRACTICES: Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/.

Bepridil exhibits anti-leukemic activity associated with NOTCH1 pathway inhibition in chronic lymphocytic leukemia

Dysregulated NOTCH1 signaling, by either gene mutations or microenvironment interactions, has been increasingly linked to chronic lymphocytic leukemia (CLL). Thus, inhibiting NOTCH1 activity represents a potential therapeutic opportunity for this disease. Using gene expression-based screening, we identified the calcium channel modulator bepridil as a new NOTCH1 pathway inhibitor. In primary CLL cells, bepridil induced selective apoptosis even in the presence of the protective stroma. Cytotoxic effects of bepridil were independent of NOTCH1 mutation and other prognostic markers. The antitumor efficacy of bepridil was associated with inhibition of NOTCH1 activity through a decrement in trans-membrane and activated NOTCH1 protein levels with unchanged NOTCH2 protein levels. In a CLL xenotransplant model, bepridil significantly reduced the percentage of leukemic cells infiltrating the spleen via enhanced apoptosis and decreased NOTCH1 activation. In conclusion, we report in vitro and in vivo anti-leukemic activity of bepridil associated with inhibition of the NOTCH1 pathway in CLL. These data provide a rationale for the clinical development of bepridil as anti-NOTCH1 targeted therapy for CLL patients.

Pharmacological conversion of atrial fibrillation in the patients of Graves' disease

BACKGROUND

Hyperthyroidism is one of the common causes of atrial fibrillation (AF), and AF is associated with increased morbidity and mortality due to thromboembolism. The sinus rhythm maintenance rate of hyperthyroidism-induced AF patients after conversion to sinus rhythm is excellent. The present study was undertaken to assess the efficacy and safety of bepridil, a multichannel blocker, in patients with hyperthyroidism-induced persistent AF.

METHODS AND RESULTS

Sixty-two patients with hyperthyroidism-induced persistent AF were treated with bepridil. Oral bepridil therapy resulted in conversion to sinus rhythm in 32 (51.6%) of the 62 patients. There were no significant differences in clinical characteristics between the responders and non-responders. At the observation period of an average of 23.9 months, the sinus rhythm maintenance rate was found to be 81.3%. Adverse effects consisted of abnormal QTc prolongation in 3 patients and sinus bradycardia in 10 patients. There was one death in which a causal association with bepridil could not be ruled out.

CONCLUSIONS

Bepridil is as beneficial treatment to convert AF for the patients with hyperthyroidism-induced persistent AF as it is for the patients with AF due to other causes. However, bepridil should be used with caution to avoid serious side effects.

Identification of FDA-approved drugs that computationally bind to MDM2

The integrity of the p53 tumor suppressor pathway is compromised in the majority of cancers. In 7% of cancers p53 is inactivated by abnormally high levels of MDM2--an E3 ubiquitin ligase that polyubiquitinates p53, marking it for degradation. MDM2 engages p53 through its hydrophobic cleft, and blockage of that cleft by small molecules can re-establish p53 activity. Small molecule MDM2 inhibitors have been developed, but there is likely to be a high cost and long time period before effective drugs reach the market. An alternative is to repurpose FDA-approved drugs. This report describes a new approach, called Computational Conformer Selection, to screen for compounds that potentially inhibit MDM2. This screen was used to computationally generate up to 600 conformers of 3244 FDA-approved drugs. Drug conformer similarities to 41 computationally-generated conformers of MDM2 inhibitor nutlin 3a were ranked by shape and charge distribution. Quantification of similarities by Tanimoto combo scoring resulted in scores that ranged from 0.142 to 0.802. In silico docking of drugs to MDM2 was used to calculate binding energies and to visualize contacts between the top-ranking drugs and the MDM2 hydrophobic cleft. We present 15 FDA-approved drugs predicted to inhibit p53/MDM2 interaction.

Relation of Interleukin-6 and C-Reactive Protein Levels to Sinus Maintenance After Pharmacological Cardioversion in Persistent Atrial Fibrillation

OBJECT

The aim of this study was to investigate whether interleukin-6 (IL-6) and C-reactive protein (CRP) have significant relation to sinus maintenance after pharmacological conversion of long-lasting atrial fibrillation (AF) with respect to use of renin-angiotensin-aldosterone system (RAS) inhibitors.

METHODS

We studied 35 consecutive patients with AF lasting > or =1 month who had successful pharmacological cardioversion with bepridil alone or in combination with aprindine. The IL-6 and CRP levels in plasma were measured after pharmacological restoration of sinus rhythm.

RESULTS

During the 1-year follow-up period, sinus rhythm was maintained in 20 patients (Group I), and the other 15 patients had recurrence of AF (Group II). Both plasma levels of IL-6 and CRP were significantly lower in Group I than in Group II (IL-6: 1.19 +/- 0.51 versus 1.84 +/- 0.66 ng/L, P < 0.005; CRP: 0.59 +/- 0.40 versus 1.24 +/- 0.79 mg/L, P < 0.005). The use of RAS inhibitors and left atrial dimension and the left ventricular ejection fraction showed no differences between the 2 groups. There was significant positive correlation between levels of IL-6 and CRP.

CONCLUSION

In long-lasting persistent AF, lower levels of IL-6 and CRP appear to be associated with maintenance of sinus rhythm after pharmacological cardioversion irrespective of the use of RAS inhibitors. Further studies are needed to clarify the role of RAS inhibitors.

Bepridil Reverses Atrial Electrical Remodeling and L-Type Calcium Channel Downregulation in a Canine Model of Persistent Atrial Tachycardia

INTRODUCTION

This study tested whether bepridil, a multichannel blocker, would reverse electrical remodeling induced by persistent atrial tachycardia.

METHODS AND RESULTS

Fourteen dogs were subjected to rapid atrial pacing at 400 bpm for 6 weeks after atrioventricular block was created to control the ventricular rate. During the study period, seven dogs were given placebo for 6 weeks (Control group), and seven were given placebo for 3 weeks, followed by 3 weeks of bepridil (10 mg/kg/day, Bepridil group). The atrial effective refractory period (ERP) and the inducibility and duration of atrial fibrillation (AF) were determined on a weekly basis. After 6 weeks, expression of L-type calcium channel alpha1C messenger ribonucleic acid (mRNA) was quantified by real-time reverse transcription-polymerase chain reaction. In the Control group, ERP was shortened and the inducibility and duration of AF increased through the 6-week period. In the Bepridil group, the same changes occurred during the first 3 weeks, but were gradually reversed with bepridil. After 6 weeks, ERP was longer, AF inducibility was lower, and AF duration was shorter in Bepridil group than in the Control group. Expression of alpha1C mRNA was decreased by 64% in the Control group (P < 0.05 vs sham), but in the Bepridil group, it was not different compared with the sham dogs. As a whole group of dogs, ERP was positively correlated with alpha1C mRNA expression.

CONCLUSION

Bepridil reverses the electrophysiological consequences of atrial remodeling to some extent and L-type calcium channel downregulation in a canine model of atrial tachycardia.

Elevation of Intracellular Ca2+ Concentration Induced by Hypoxia in Retinal Ganglion Cells

PURPOSE

To analyze the mechanism of hypoxia-induced changes of the intracellular Ca(2+) concentration ([Ca(2+)](i)) in retinal ganglion cells (RGCs).

METHODS

Fluo-3 was applied to the cut edge of the optic nerve of 6-week-old rats. The retina was sliced, and the Ca images were captured. A hypoxic condition was created by superfusing the retinal slice with an oxygen/glucose-deprived solution.

RESULTS

The retrograde staining method filled the RGCs selectively. Fifteen minutes of hypoxic conditions induced an increase in [Ca(2+)](i) in the RGCs (Delta0.13 +/- 0.03, n = 23). Application of 60 microM DL-2-amino-5-phosphonovaleric acid partially blocked the hypoxia-induced [Ca(2+)](i) increase in dendrites (Delta0.03 +/- 0.02, n = 4, P < 0.05) but not in the somata (Delta0.12 +/- 0.02, n = 9). The RGC dendrites showed a further increase in [Ca(2+)](i) after being switched back to an oxygenated solution (Delta0.14 +/- 0.04, n = 4). Neither 6-cyano-7-nitroquinoxaline-2,3-dione disodium, DL: -threo-beta-benzyloxyaspartate, nifedipine, nor bepridil inhibited the hypoxia-induced [Ca(2+)](i) increase. A Ca(2+)-free superfusion prevented the hypoxia-induced [Ca(2+)](i) increase in the somata (Delta0.07 +/- 0.02, n = 5, P < 0.05) but not in the dendrites (Delta0.16 +/- 0.005, n = 4).

CONCLUSIONS

The mechanism of the hypoxia-induced increase in [Ca(2+)](i) differs between somata and dendrites. The N-methyl-D-aspartate channel of dendrites seems to be the main route of Ca(2+) influx.

Amiodarone and bepridil inhibit anthrax toxin entry into host cells

Anthrax lethal toxin is one of the fundamental components believed to be responsible for the virulence of Bacillus anthracis. In order to find novel compounds with anti-lethal toxin properties, we used a cell-based assay to screen a collection of approximately 500 small molecules. Nineteen compounds that blocked lethal toxin-mediated killing of RAW 264.7 macrophages were identified, and we report here on the characterization of the two most potent antitoxic compounds, amiodarone and bepridil. These drugs are used to treat cardiac arrhythmia or angina in humans at doses similar to those that provide protection against lethal toxin in vitro. Our results support a model whereby the antitoxic properties of both drugs result from their ability to block endosomal acidification, thereby blocking toxin entry. Amiodarone was tested in vivo and found to significantly increase survival of lethal toxin-challenged Fischer rats.

Neuronal preconditioning with the antianginal drug, bepridil

It has recently been shown that the antianginal drug bepridil (BEP) activates mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels and thus confers cardioprotection. Our aim was to investigate whether BEP could induce preconditioning in cultured rat cortical neurons. Although BEP depolarized isolated and in situ mitochondria and increased reactive oxygen species generation, no acute protection was observed. However, a 3-day BEP-treatment elicited dose-dependent delayed neuroprotection against 180 min of oxygen-glucose deprivation (cell viability: untreated, 52.5 +/- 0.85%; BEP 1 micromol/L, 59.6 +/- 1.53%*; BEP 2.5 micromol/L, 71.9 +/- 1.23%*; BEP 5 micromol/L, 95.3 +/- 0.89%*; mean +/- SEM; *p < 0.05 vs. untreated) and 60 min of glutamate excitotoxicity (200 micromol/L; cell viability: untreated, 54.1 +/- 0.69%; BEP 1 micromol/L, 61.2 +/- 1.19%*; BEP 2.5 micromol/L, 78.1 +/- 1.67%*; BEP 5 micromol/L, 91.2 +/- 1.20%*; mean +/- SEM; *p < 0.05 vs. untreated), and inhibited the reactive oxygen species surge upon glutamate exposure. The protection was antagonized with co-application of the superoxide dismutase mimetic M40401, but not with reduced glutathione, catalase, or with the mitoK(ATP) blocker 5-hydroxydecanoate. Furthermore, BEP treatment resulted in increased levels of phosphorylated protein kinase C, manganese-dependent superoxide dismutase, glutathione peroxidase, and Bcl-2. Our results indicate that BEP induces delayed neuronal preconditioning which is dependent on superoxide generation but perhaps not on direct mitoK(ATP) activation.

Involvement of Na+-Ca2+ exchanger on metabotropic glutamate receptor 1-mediated [Ca2+]i transients in rat cerebellar Purkinje neurons

Cerebellar Purkinje neurons have intracellular regulatory systems including Ca2+-binding proteins, intracellular Ca2+ stores, Ca2+-ATPase and Na+-Ca2+ exchanger (NCX) that keep intracellular Ca2+ concentration ([Ca2+]i) in physiological range. Among these, NCX interacts with AMPA receptors, activation of which induces cerebellar synaptic plasticity. And the activation of metabotropic glutamate receptor 1 (mGluR1) is also involved in the induction of cerebellar long-term depression. The interaction of NCX with mGluR1 is not known yet. Thus, in this study, the functional relationship between NCX and mGluR1 in modulating the [Ca2+]i in rat Purkinje neurons was investigated. The interaction between NCX and mGluR1 in Purkinje neurons was studied by measuring intracellular Ca2+ transients induced by an agonist of group I mGluRs, 3,5-dihydroxyphenylglycine (DHPG). The DHPG-induced Ca2+ transient was significantly reduced by treatments of NCX inhibitors, bepridil and KB-R7943. When cells were pretreated with antisense oligodeoxynucleotides of NCX, the DHPG-induced Ca2+ transient was also inhibited. These results suggest that NCX modulates the activity of mGluR1 in cerebellar Purkinje neurons. Therefore, NCX appears to play an important role in the physiological function of cerebellar Purkinje neurons such as synaptic plasticity.

Cardiac electrophysiologic interactions of bepridil, a new calcium antagonist, with enflurane, halothane, and isoflurane

Bepridil is an investigational calcium antagonist that also has fast sodium channel blocking and antidysrhythmic properties. In the present study, the potential interactions of bepridil with volatile anesthetics on cardiac electrophysiologic parameters were evaluated in open-chest dogs. Twenty-four dogs anesthetized with enflurane (n=6), halothane (n=6), isoflurane (n=6), or chloralose (n=6) received 2.5 mg/kg of bepridil intravenously (IV). Twenty-five additional dogs anesthetized with enflurane (n=7), halothane (n=6), isoflurane (n=6), or chloralose (n=6), received bepridil, 5.0 mg/kg, IV. Dogs anesthetized with cloralose served as controls. Cardiac electrophysiologic parameters were measured after the dogs were anesthetized and were repeated 5, 15, 30, 45, and 60 minutes after bepridil infusion. Plasma bepridil concentrations were also determined at the above time points. Synergy between bepridil and enflurane was demonstrated in the following cardiac electrophysiologic parameters: depression of sinus node function as evidenced by severe depression of sinus node automaticity and conduction; depression of atrioventricular function as evidenced by prolongation of the atrial-His bundle interval and the Wenckebach R-R interval; and, prolongation of the atrial effective refractory period. No synergy was demonstrated between bepridil and halothane or isoflurane when compared to bepridil's effects during chloralose anesthesia. It is concluded that significant synergistic cardiac electrophysiologic effects exist between bepridil and enflurane in dogs. It is recommended that caution be used when anesthetizing patients receiving bepridil with enflurane until human data on the use of this combination of pharmacologic agents is available.

The influence of sodium–calcium exchange inhibitors on rabbit lens ion balance and transparency

Calcium regulation is essential to the maintenance of lens transparency. To maintain cytoplasmic calcium concentration at the required low level the lens must export calcium continuously. Here, studies were conducted to test whether sodium-calcium exchanger (NCX) inhibitors disturb calcium balance in the rabbit lens. Intact lenses were incubated up to 48 h in the presence or absence of the NCX inhibitor bepridil. Lens sodium, potassium and calcium content were determined by atomic absorption spectrophotometry. Fluo-4 was used to measure epithelial cell cytoplasmic calcium concentration in an intact lens preparation. NCX1 protein expression in lens epithelium was examined by western blot. NCX1 band density was similar in central and equatorial epithelium samples. Lenses exposed to bepridil (30 microM) lost transparency at the anterior and exhibited significant changes in electrolyte and water content. After 48 h, lens calcium content more than doubled, sodium increased four fold and potassium was significantly reduced. In contrast, lenses exposed to inhibitors of reverse mode calcium transport by NCX (KBR7943 or SN-6) remained transparent and the electrolyte and water content of the lens remained unchanged. The ability of bepridil to cause significant changes in lens transparency and electrolyte content points to an important role for NCX-meditated calcium export in the lens.

Na+/Ca2+ exchanger inhibitors modify the accumulation of tumor-diagnostic PET tracers in cancer cells

AIM

To establish the effects of Na(+)/Ca(2+) exchanger (NCX) blockers on 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)FDG) and (11)C-choline accumulation in different cancer cells.

METHODS

The tumor cells were incubated with NCX inhibitors, and the uptakes of (18)FDG and (11)C-choline were measured. Flow cytometric measurements of intracellular Ca(2+) and Na(+) concentrations were carried out. The presence of the NCX antigen in the cancer cells was proved by Western blotting, flow cytometry and confocal laser scanning microscopy.

RESULTS

The NCX is expressed at a noteworthy level in the cytosol and on the cytoplasmic membrane of the examined cells. Incubation of the cells with three chemically unrelated NCX blockers (bepridil, KB-R7943 or 3',4'-dichlorobenzamil hydrochloride) resulted in an increase in the intracellular Ca(2+) concentration, with a simultaneous decrease in the intracellular Na(+) concentration. The treatment with the NCX inhibitors increased the energy consumption of the tumor cells by 50-100%. Thapsigargin abolished the NCX-induced (18)FDG accumulation in the cells. The NCX blockers applied decreased the (11)C-choline accumulation of all the investigated cancer cells by 60-80% relative to the control.

CONCLUSION

A possible masking effect of NCX medication must be taken into consideration during the diagnostic interpretation of PET scans.

Pharmacological activation and inhibition of Slack (Slo2.2) channels

The Slack (Sequence like a calcium-activated K channel) (Slo2.2) gene is abundantly expressed in the mammalian brain and encodes a sodium-activated K+ (KNa) channel. Although the specific roles of Slack channel subunits in neurons remain to be identified, they may play a role in the adaptation of firing rate and in protection against ischemic injury. In the present study, we have generated a stable cell line expressing the Slack channel, and have analyzed the pharmacological properties of these channels in these cells and in Xenopus oocytes. Two known blockers of KNa channels, bepridil and quinidine, inhibited Slack currents in a concentration-dependent manner and decreased channel activity in excised membrane patches. The inhibition by bepridil was potent, with an IC50 of 1.0 microM for inhibition of Slack currents in HEK cells. In contrast, bithionol was found to be a robust activator of Slack currents. When applied to the extracellular face of excised patches, bithionol rapidly induced a reversible increase in channel opening, suggesting that it acts on Slack channels relatively directly. These data establish an important early characterization of agents that modulate Slack channels, a process essential for the experimental manipulation of Slack currents in neurons.

Iron ions derived from the nitric oxide donor sodium nitroprusside inhibit mineralization

Sodium nitroprusside (SNP) is a nitric oxide (NO) donor drug, which is therapeutically used as a vasodilating drug in heart transplantations. In our previous study it was found that SNP at a concentration of 100 microM inhibited mineralization in a cell culture system, indicating that the beneficial effects of this drug may also include inhibition of vascular calcification. The aim of this study was to investigate which bioactive compounds generated from SNP inhibit mineralization. ATDC5 cells were grown for 14 days and mineralization was induced by addition of 5 mM phosphate for 24 h. Mineralization was determined by staining precipitated calcium with an alizarin red stain. It was found that the NO donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine were not able to inhibit mineralization and NO scavengers could not antagonize the inhibiting effect of SNP on mineralization. The iron chelator deferoxamine (200 microM) antagonized the inhibiting effect on mineralization mediated by SNP and ammonium iron sulfate inhibited mineralization in a dose-dependent manner (10-100 microM). Furthermore, iron ions (30 microM) were detected to be released from SNP in the cell culture. These data show that the iron moiety of sodium nitroprusside, rather than nitric oxide inhibits mineralization.

Studies of the effect of ionomycin on the KCNQ4 channel expressed in Xenopus oocytes

The effect of ionomycin on the human KCNQ4 channels expressed in Xenopus leavis oocytes was investigated. KCNQ4 channels expressed in Xenopus oocytes were measured using two-electrode voltage clamp. The activation of KCNQ4 current had slow activation kinetics and low threshold (approximately -50 mV). The expressed current of KCNQ4 showed the half-maximal activation (V(1/2)) was -17.8 mV and blocked almost completely by KCNQ4 channel blockers, linopirdine (300 microM) or bepridil (200 microM). The significant increase of KCNQ4 outward current induced by ionomycin (calcium salt) is about 1.7-fold of control current amplitude at +60 mV and shifted V(1/2) by approximately -8 mV (from -17.8 to -26.0 mV). This effect of ionomycin could be reversed by the further addition of BAPTA-AM (0.3 mM), a membrane-permeable calcium chelator. Furthermore, the increased effect of ionomycin on KCNQ4 current is abolished by pretreatment of linopirdine or bepridil. In contrast, direct cytoplasmic injection of calcium medium (up to 1 mM calcium, 50 nl) did not mimic the effect of ionomycin. In conclusion, the effect of ionomycin on enhancement of KCNQ4 current is independent of intracellular calcium mobilization and possibly acts on intramembrane hydrophobic site of KCNQ4 protein expressed in Xenopus oocytes.

Bepridil inhibits sub-acute phase of atrial electrical remodeling in canine rapid atrial stimulation model

Background The effect of bepridil, a multichannel blocker, on atrial electrical remodeling was evaluated in a canine rapid atrial stimulation model. Methods and Results In 10 beagle dogs, the right atrial appendage (RAA) was paced at 400 beats/min for 2 weeks. The atrial electrophysiological parameters, including effective refractory period (AERP), were evaluated at three atrial sites: RAA, the right atrium close to the inferior vena cava (IVC) and the left atrium (LA), during the time course of rapid pacing. Five of the dogs were given bepridil (10 mg . kg (-1) . day(-1) po). In the control group, AERP was significantly shortened at all atrial sites and the AERP shortening (DeltaAERP) was larger for the RAA and LA than at the IVC site (p<0.05). In the bepridil group, DeltaAERP was smaller than that of the controls at all atrial sites, and the AERP started to return slowly to the pre-pacing level in the second week, regardless of the continuation of rapid pacing. Conclusions In a canine rapid atrial stimulation model, bepridil suppressed AERP shortening. Bepridil might have a reverse electrical remodeling effect, at least for AERP shortening, because it showed slow recovery of AERP in the subacute phase of rapid atrial pacing. (Circ J 2006; 70: 206 - 213).

Chronic hypoxia inhibits Na+/Ca2+ exchanger expression in cortical astrocytes

Ca signalling is central to many diverse functions of astrocytes. Of the numerous proteins involved in Ca homeostasis, the Na(+)/Ca(2+) exchanger is of particular importance in signalling regulation. We have shown that Ca signaling is dramatically remodelled in astrocytes by periods of chronic hypoxia, in part by inhibition of Na(+)/Ca(2+) exchanger. Here, we demonstrate that bepridil-sensitive Ca extrusion (indicative of Na(+)/Ca(2+) exchanger activity) is suppressed following 24 h hypoxia (2.5 or 1% O2) owing to a loss of Na(+)/Ca(2+) exchanger expression, as determined using immunocytochemistry and Western blots. Hypoxic Na(+)/Ca(2+) exchanger 1 inhibition occurs at the level of transcription, as mRNA for Na(+)/Ca(2+) exchanger 1 was significantly suppressed by hypoxia. Our results show hypoxia perturbs Ca homeostasis in astrocytes via the suppression of Na(+)/Ca(2+) exchanger 1 expression.

Role of the Na+/Ca2+ exchanger in calcium homeostasis and human sperm motility regulation

A number of cell functions, such as flagellar beating, swimming velocity, acrosome reaction, etc., are triggered by a Ca2+ influx across the cell membrane. For appropriate physiological functions, the motile human sperm maintains the intracellular free calcium concentration ([Ca2+]i) at a submicromolar level. The objective of this study was to determine the role of the Na+/Ca2+ exchanger (NCX) in the maintenance of [Ca2+]i in human spermatozoa. Spermatozoa maintained in extracellular medium containing>or=1 microM Ca2+ exhibited motility similar to that of the control. In addition to several calcium transport mechanisms described earlier, we provide evidence that the NCX plays a crucial role in the maintenance of [Ca2+]i. Three chemically unrelated inhibitors of the NCX (bepridil, DCB (3',4'-dichlorobenzamil hydrochloride), and KB-R7943) all blocked human sperm motility in a dose and incubation time dependent manner. The IC50 values for bepridil, DCB, and KB-R7943 were 16.2, 9.8, and 5.3 microM, respectively. The treatment with the above-mentioned blockers resulted in an elevated [Ca2+]i and a decreased [Na+]i. The store-operated calcium channel (SOCC) inhibitor SKF 96365 also blocked the sperm motility (IC50=2.44 microM). The presence of the NCX antigen in the human spermatozoa was proven by flow cytometry, confocal laser scanning microscopy, and immunoblotting techniques. Calcium homeostasis of human spermatozoa is maintained by several transport proteins among which the SOCC and the NCX may play a major role.

Repolarization dynamics in patients with idiopathic ventricular fibrillation: pharmacological therapy with bepridil and disopyramide

The electrocardiographic parameters relating occurrence of ventricular fibrillation (VF) episodes in patients with idiopathic VF (IVF) are still unknown. The aim of this study was to clarify efficacy of pharmacological therapy in patients with IVF with respect to repolarization dynamics. The study group consisted of 8 men (age 43.6 +/- 9.1 years) with IVF (Brugada type 5 patients, prominent J wave in the inferior leads 3 patients) who had documented spontaneous episodes of VF, 7 of whom had implantable cardioverter defibrillators. The relation between QT and RR interval was analyzed from 24-hour Holter ECG using an automatic analyzing system before and after pharmacological therapy (bepridil 5 and disopyramide 3). From QT-RR linear regression lines, QT intervals were determined at RR intervals of 0.6 second [QT(0.6)], 1.0 second [QT(1.0)], and 1.2 seconds [QT(1.2)]. Pharmacological therapy increased the slope of QT-RR regression line from 0.105 +/- 0.020 to 0.144 +/- 0.037 (P < 0.05). Accordingly, QT(1.0) and QT(1.2) became longer after drug therapy [QT(1.0), 0.382 +/- 0.016 seconds vs 0.414 +/- 0.016 seconds (P < 0.01); QT(1.2), 0.403 +/- 0.017 seconds vs 0.442 +/- 0.021 seconds (P < 0.01)]. However, QT(0.6) did not change after drug administration. Before drug therapy the average episodes of VF were 5.5 +/- 5.8 (range 1 to 17) during the observation period of 19.3 +/- 17.6 months (range 6 to 60 months). After drug therapy, 6 patients had no episode of VF for 24 to 120 months (66.0 +/- 38.5 months). Two patients had a single episode of VF for 12- and 96-month follow-ups. Pharmacological therapy decreased the frequency of VF episodes in association with prolongation of QT intervals at slower heart rates. Not only J wave and ST elevation but also shorter QT intervals at slower heart rates may represent an electrophysiological substrate for development of VF episodes in these specific IVF patients.

Bepridil, an antiarrhythmic drug, opens mitochondrial KATP channels, blocks sarcolemmal KATP channels, and confers cardioprotection

Bepridil, which is clinically useful in the treatment of arrhythmias, has been reported to inhibit sarcolemmal ATP-sensitive K(+) (sarcK(ATP)) channels. However, the effect of bepridil on mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channels remains unclear. The objective of the present study was to determine whether bepridil activates mitoK(ATP) channels and confers cardioprotection. SarcK(ATP) channels composed of Kir6.2+SUR2A in human embryonic kidney (HEK) 293 cells were examined using the patch-clamp technique. Flavoprotein fluorescence in guinea pig ventricular cells and matrix volume in isolated rat heart mitochondria were measured to assay mitoK(ATP) channel activity. Mitochondrial Ca(2+) concentration ([Ca(2+)](m)) was measured by loading cells with rhod-2 fluorescence. Coronary-perfused guinea pig ventricular muscles were subjected to 35-min no-flow ischemia followed by 60-min reperfusion. Bepridil (10 microM) completely inhibited the pinacidil-induced Kir6.2+SUR2A channel current expressed in HEK 293 cells. Bepridil reversibly oxidized the flavoprotein and increased mitochondrial matrix volume in a concentration-dependent manner. Furthermore, bepridil significantly attenuated the ouabain-induced increase of [Ca(2+)](m). Pretreatment with bepridil for 5 min before ischemia improved the recovery of developed tension measured after 60 min of reperfusion. These effects of bepridil were abolished by the mitoK(ATP) channel blocker 5-hydroxydecanoate (500 microM) and by the nonselective K(ATP) channel blocker glisoxepide (10 microM). Our results indicate that bepridil is an opener of mitoK(ATP) channels but an inhibitor of sarcK(ATP) channels and exerts a direct cardioprotective effect on native cardiac myocytes. This is the first report of a unique modulator of K(ATP) channels; bepridil would be expected to mitigate ischemic injury while blunting arrhythmias.

Involvement of Na+-Ca2+ exchanger in intracellular Ca2+ increase and neuronal injury induced by polychlorinated biphenyls in human neuroblastoma SH-SY5Y cells

In SH-SY5Y, a human neuroblastoma cell line, Aroclor 1254 (A1254), induced a dose-dependent (10-50 microg/ml) intracellular calcium concentration ([Ca2+]i) increase. Two rather specific sodium-calcium (Na+-Ca2+) exchanger (NCX) inhibitors, bepridil (10 microM) and KB-R7943 [2-[2-[4-(4-nitrobenzyloxy) phenyl]ethyl]isothiourea methanesulfonate] (10 microM), reduced A1254-induced [Ca2+]i increase. A 24-h exposure to 30 microg/ml A1254 caused remarkable SH-SY5Y neuroblastoma cell damage. It is noteworthy that both bepridil and KB-R7943 counteracted A1254-induced neuronal injury. These results indicate that NCX contributes to [Ca2+]i increase and neuronal injury induced by A1254. RT-PCR experiments revealed in SH-SY5Y neuroblastoma cells the expression of NCX1 and NCX3 isoforms. To investigate which isoform was involved in [Ca2+]i increase and neuronal damage induced by A1254, we used specific antisense oligodeoxynucleotides (ODNs) to reduce NCX1 or NCX3 protein expression. The results showed that only NCX1 ODN reduced [Ca2+]i increase and neuronal injury induced by A1254. In conclusion, these results indicate that NCX1 may participate to [Ca2+]i increase and neurotoxicity evoked by A1254 in SH-SY5Y neuroblastoma cells.

Effects of Na+-Ca2+ exchanger activity on the alpha-amino-3-hydroxy-5-methyl-4-isoxazolone-propionate-induced Ca2+ influx in cerebellar Purkinje neurons

Variations in intracellular calcium activity ([Ca2+]i) play crucial roles in information processing in Purkinje neurons such as synaptic plasticity. Although Na+-Ca2+ exchanger (NCX) has been shown to participate in the regulation of homeostasis and secretion in neuronal cells, the physiological role of NCX in Purkinje neurons, such as a role in cerebellar synaptic plasticity, is not well understood. NCX in acutely dissociated rat Purkinje neurons was identified by double staining with anti-calbindin D-28k antibody and anti-NCX antibody. The physiological activity of NCX was examined by measuring transient intracellular Ca2+ changes resulting from the Ca2+ influx via reverse mode of NCX (with 0 mM Na+/2.5 mM Ca2+ solutions) and the efflux via the forward mode of NCX (with 140 mM Na+/0 mM Ca2+ solutions). This transient increase in Ca2+ concentration was not elicited in the cells pretreated with NCX antisense oligodeoxynucleotides. And the Ca2+ influx resulting from the reverse mode of NCX was significantly reduced by 2-[2-[4-(4-nitrobenyloxy) phenyl] ethyl] isothiourea methanesulfonate, while the Ca2+ efflux via forward mode was inhibited by bepridil. The physiological role of NCX in synaptic function was studied by measuring Ca2+ transients induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolone-propionate (AMPA) receptor activation. This AMPA-evoked response was decreased with the inhibition of NCX forward mode and also, to less degree, with the inhibition of reverse mode. In antisense oligodeoxynucleotides pretreated cells, the AMPA-evoked response was also reduced, as was the case in NCX-inhibitor treated cells. The inhibition of NCX activity had depressant effects on Ca2+ transients induced by AMPA receptor activation. These results suggest that NCX plays a physiological role in modulating the activity of cerebellar Purkinje neurons, such as synaptic plasticity, via interaction with AMPA receptors in Purkinje neurons.

Voltage-dependent and frequency-independent inhibition of recombinant Cav3.2 T-type Ca2+ channel by bepridil

Effects of bepridil on the low voltage-activated T-type Ca2+ channel (CaV3.2) current stably expressed in human embryonic kidney (HEK)-293 cells were examined using patch-clamp techniques. Bepridil potently inhibited ICa,T with a markedly voltage-dependent manner; the IC50 of bepridil was 0.4 micromol/l at the holding potential of -70 mV, which was 26 times as potent as that at -100 mV (10.6 micromol/l). Steady-state inactivation curve (8.4 +/- 1.7 mV) and conductance curve (5.9 +/- 1.9 mV) were shifted to the hyperpolarized potential by 10 micromol/l bepridil. Bepridil exerted the tonic blocking action but not the use-dependent block. Bepridil had no effect on the recovery from inactivation of T-type Ca2+ channels. Thus, high efficacy of bepridil for terminating atrial fibrillation and atrial flutter may be considered to be attributed, at least in a part, to the T-type Ca2+ channel-blocking actions.

Influence of different calcic antagonists on the Caco-2 cell monolayer integrity or “TEER, a measurement of toxicity ?”

The purpose of this work was to investigate the interest of the TEER measurement, a quite simple measure, as an evaluation of toxicity, in function of time and level of drug in the experimental medium, for different anticalcic agents. The extend of the increase and decrease of TEER, was evaluated by measuring the TEERmax and calculating the TEER50 respectively. Three groups of compounds could be therefore considered. The first, characterized by a quite short period of TEER increase, followed by an extremely rapid decrease (high values of TEER50), included perhexiline and prenylamine. The most toxic compounds, the second one, characterized by the smallest variations of TEER, included verapamil and diltiazem. This group was related with the less toxic compounds, the third group, represented by bepridil, characterized by dependant-dose TEERmax and TEER50. Therefore, the TEER measurement appeared as a quite simple approach of comparative toxicity of anticalcic agents.

Effects of blockers of Ca2+ channels and other ion channels on in vitro excystment of Paragonimus ohirai metacercariae induced by sodium cholate

The inhibitory effects of various ion channel blockers were examined on in vitro excystment of Paragonimus ohirai metacercariae induced by a bile salt, sodium cholate. At a concentration of 10 microM, bepridil, a non-selective Ca(2+) channel blocker, completely inhibited in vitro excystment, whereas TEA, lidocaine, and R(+)-IAA-94, channel blockers against K(+), Na(+) and Cl(-) ions, respectively, benzamil, an Na(+)/H(+) and Na(+)/Ca(2+) ion exchanger blocker, and R(+)-DIOA, a [K(+), Cl(-)] cotransporter inhibitor, did not. Considering the previous result that Ca(2+) ionophores are also efficient inducing factors for in vitro excystment of P. ohirai metacercariae and the present result, bile salts appear to induce the excystment of P. ohirai metacercariae through evoking the Ca(2+) channels of target cells within the metacercarial juveniles.

Design, synthesis, and biological evaluation of novel T-Type calcium channel antagonists

This paper describes the synthesis of several novel T-type calcium channel antagonists that inhibit calcium influx into the cell, which in turn regulates unknown aspects of the cell cycle pathway that are responsible for cellular proliferation. A library of compounds was synthesized and a brief structure activity relationship will be described. From these studies we have identified a compound (1) that displays anti-proliferative activity in the low micromolar range across a variety of cancer cell lines.

Evidence for a protective role played by the Na+/Ca2+ exchanger in cerebral ischemia induced by middle cerebral artery occlusion in male rats

In the present paper, the role played by Na+/Ca2+ exchanger (NCX) in focal cerebral ischemia was investigated. To this aim, permanent middle cerebral artery occlusion (pMCAO) was performed in male rats. The effects on the infarct volume of some inhibitors, such as tyrosine-6 glycosylated form of the exchanger inhibitory peptide (GLU-XIP), benzamil derivative (CB-DMB) and diarylaminopropylamine derivative (bepridil), and of the NCX activator, FeCl3, were examined. FeCl3, CB-DMB, bepridil and GLU-XIP, a modified peptide synthesized in our laboratory in order to facilitate its entrance into the cells through the glucose transporter, were intracerebroventricularly (i.c.v.) infused. FeCl3 (10 microg/kg) was able to reduce the extension of brain infarct volume. This effect was counteracted by the concomitant icv administration of CB-DMB (120 microg/kg). All NCX inhibitors, GLU-XIP, CB-DMB and bepridil, caused a worsening of the brain infarct lesion. These results suggest that a stimulation of NCX activity may help neurons and glial cells that are not irreversibly damaged in the penumbral zone to survive, whereas its pharmacological blockade can compromise their survival.

Differential effect of HERG blocking agents on cardiac electrical alternans in the guinea pig

Beat-to-beat alternations of the cardiac monophasic action potential, known as electrical alternans, were studied at drug concentrations that have known arrhythmogenic outcomes. Electrical alternans were elicited from the heart of anesthetized guinea pigs, both in the absence and presence of drugs that inhibit the delayed rectifier K(+) channel encoded by the human ether a-go-go related-gene (HERG), and are associated with the fatal arrhythmia, Torsade de Pointes. Two other HERG inhibiting drugs not associated with Torsade de Pointes were also studied. At concentrations known to be proarrhythmic, E-4031 and bepridil increased mean alternans 10 and 40 ms at pacing frequencies </=160 ms. Terfenadine and cisapride both increased mean alternans up to 20 and 21 ms, respectively, at pacing frequencies of </=150 ms. On the other hand, verapamil and risperidone showed no increase in mean alternans while risperidone significantly reduced alternans at concentrations up to 74 times its therapeutic level. The magnitude of effect on rate-dependent alternans may allow the differentiation of proarrhythmia and non-arrhythmic HERG blockers at clinically relevant concentrations.

Bepridil Block of Recombinant Human Cardiac IKs Current Shows a Time-Dependent Unblock

Whole-cell patch-clamp techniques were employed to examine the effects of bepridil, a Ca2+ channel blocker with Vaughan Williams class III action, on a slow component of cardiac delayed rectifier K+ current (IKs), which was reconstituted in HEK293 cells by transfecting KCNQ1 and KCNE1. Micromolar bepridil inhibited tail currents carried by KCNQ1/KCNE1 channels in a concentration-dependent manner (IC50 = 5.3 +/- 0.7 microM at -40 mV from 1000 milliseconds test pulse). When the effect of the drug was examined with a short test pulse protocol (250 milliseconds), IC50 became two-fold smaller than that measured with 1000 milliseconds test pulse (2.5 +/- 0.8 microM). The envelope-of-tails protocol was used to assess how the duration of depolarizing pulse affects the drug action on the outward KCNQ1/KCNE1 channel current. The drug significantly inhibited tail currents more potently during shorter pulses (<600 milliseconds). Bepridil's block was therefore time dependent, and its binding affinity to the channel was greater in the closed state channel, as evidenced by unblocking during prolonged depolarization. These properties of channel blockade appear to underscore the mechanism of bepridil's effect on IKs current.

Sodium-calcium exchange influences the response to endothelin-1 in lens epithelium

Studies were conducted to examine the possible involvement of Na+-Ca2+ exchanger in determining the magnitude of the endothelin-1 (ET-1)-receptor-mediated calcium signal in porcine lens epithelial cells. Cytoplasmic calcium concentration was measured in primary cultured cells loaded with Fura-2. ET-1 (100 nM) caused cytoplasmic calcium to increase transiently to approximately 250 nM from a baseline of approximately 65 nM. The calcium increase decayed to a sustained plateau 35-45 nM above the baseline. Both the peak and plateau component of the ET-1 calcium response were abolished by PD145065, an ET receptor antagonist, and by cyclopiazonic acid (CPA) (10 microM). In calcium-free bathing solution, only the plateau was abolished. In the presence of ouabain, low-sodium bathing solution or bepridil, a sodium-calcium exchange inhibitor, peak height more than doubled. Bepridil also increased the peak height of the calcium response to ATP. The half-time for decay of the ET-1 and ATP calcium peak was increased several folds by bepridil, ouabain and low-sodium conditions. Measurements of ionomycin-releasable calcium suggested calcium store size was not increased in bepridil-treated cells. Taken together findings suggest inhibition of sodium-calcium exchange increases the magnitude of the receptor-initiated store-release phase of the ET-1 calcium signaling response as the result of impaired calcium clearance from the cytoplasm.

Na(+)/Ca(2+) exchanger in porcine oocytes

The presence of the Na(+)/Ca(2+) exchange mechanism was investigated in porcine oocytes. Immature and in vitro-matured oocytes were loaded with the Ca(2+)-sensitive fluorescent dye fura 2 and changes in the intracellular free Ca(2+) concentration ([Ca(2+)](i)) were monitored after altering the Na(+) concentration gradient across the plasma membrane. Decreasing the extracellular Na(+) concentration induced an increase in [Ca(2+)](i) possibly by a Ca(2+) influx via the Na(+)/Ca(2+) exchanger. A similar Ca(2+) influx could also be triggered after increasing the intracellular Na(+) concentration by incubation in the presence of ouabain (0.4 mM), a Na(+)/K(+)-ATPase inhibitor. The increase in the [Ca(2+)](i) was due to Ca(2+) influx since it was abolished in the absence of extracellular Ca(2+), and the increase was mediated by the Na(+)/Ca(2+) exchanger since it was blocked by the application of amiloride or bepridil, inhibitors of Na(+)/Ca(2+) exchange. Verapamil (50 micro M) and pimozide (50 micro M), inhibitors of L- and T-type voltage-gated Ca(2+) channels, respectively, could not block the Ca(2+) influx. The Ca(2+) entry via the Na(+)/Ca(2+) exchanger could not induce the release of cortical granules and did not stimulate the resumption of meiosis. This was unexpected because Ca(2+) is thought to be a universal trigger for activation. Using antibodies raised against the exchanger, it was demonstrated that the Na(+)/Ca(2+) exchanger was localized predominantly in the plasma membrane. Reverse transcription-polymerase chain reaction revealed that porcine oocytes contain a transcript that shows 98.1% homology to the NACA3 isoform of the porcine Na(+)/Ca(2+) exchanger.

Blockers of sodium and calcium entry protect axons from nitric oxide-mediated degeneration

Axonal degeneration can be an important cause of permanent disability in neurological disorders in which inflammation is prominent, including multiple sclerosis and Guillain-Barré syndrome. The mechanisms responsible for the degeneration remain unclear, but it is likely that axons succumb to factors produced at the site of inflammation, such as nitric oxide (NO). We previously have shown that axons exposed to NO in vivo can undergo degeneration, especially if the axons are electrically active during NO exposure. The axons may degenerate because NO can inhibit mitochondrial respiration, leading to intraaxonal accumulation of Na(+) and Ca(2+) ions. Here, we show that axons can be protected from NO-mediated damage using low concentrations of Na(+) channel blockers, or an inhibitor of Na(+)/Ca(2+) exchange. Our findings suggest a new strategy for axonal protection in an inflammatory environment, which may be effective in preventing the accumulation of permanent disability in patients with neuroinflammatory disorders.

Possible role of calcium ions, calcium channels and calmodulin in excystation and metacystic development of Entamoeba invadens

The effect of calcium ions (Ca(2+)) and calmodulin (CaM) on the excystation and metacystic development of Entamoeba invadens was examined by transfer of cysts to a growth medium containing calcium antagonists and CaM inhibitors. Excystation, which was assessed by counting the number of metacystic amoebae after induction of excystation, was inhibited by the calcium chelators ethyleneglycol bis (beta-aminoethyl ether)- N,N'-tetraacetate (EGTA) and ethylene-diaminetetraacetate (EDTA), with EDTA being more potent than EGTA. The inhibitory effect of higher concentrations of these chelators on excystation was associated with reduced viability of cysts. Metacystic development, when determined by the number of nuclei in an amoeba, was delayed by EGTA, because the percentage of four-nucleate amoebae was higher than in controls at day 3 of incubation. EDTA made metacystic development unusual by producing a large number of metacystic amoebae with more than ten nuclei. The inhibition of excystation by these chelators was partially abrogated by their removal. A putative antagonist of intracellular calcium flux, 8-( N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8) also inhibited the excystation and metacystic development, but had little effect on cyst viability. The slow Na(+)-Ca(2+) channel blocker bepridil but not verapamil inhibited the excystation and metacystic development, associating with reduced cyst viability at higher concentrations. The inhibitory effect of bepridil on excystation was abrogated by removal of the drug. The CaM inhibitor trifIuoperazine (TFP) but not W-7 [ N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide] inhibited the excystation and metacystic development. The inhibitory effect of TFP on excystation was also abrogated by removal of the drug. These results indicate that extracellular calcium ions, amoebic intracellular calcium flux, calcium channels, and a CaM-dependent process contribute to the excystation and metacystic development of E. invadens.

Motility initiation in herring sperm is regulated by reverse sodium-calcium exchange

Sperm of the Pacific herring, Clupea pallasi, are unique in that they are immotile upon spawning in the environment. Herring sperm have evolved to remain motionless for up to several days after spawning, yet are still capable of fertilizing eggs. An egg chorion ligand termed "sperm motility initiation factor" (SMIF) induces motility in herring sperm and is required for fertilization. In this study, we show that SMIF induces calcium influx, sodium efflux, and a membrane depolarization in herring sperm. Sperm motility initiation by SMIF depended on decreased extracellular sodium (<350 mM) and could be induced in the absence of SMIF in very low sodium seawater. Motility initiation depended on > or =1 mM extracellular calcium. Calcium influx caused by SMIF involved both the opening of voltage-gated calcium channels and reverse sodium-calcium (Na(+)/Ca(2+)) exchange. Membrane depolarization was slightly inhibited by a calcium channel blocker and markedly inhibited by a Na(+)/Ca(2+) exchange inhibitor. Sodium efflux caused by SMIF-initiated motility was observed when using both extracellular and intracellular sodium probes. A Na(+)/Ca(2+) exchange antigen was shown to be present on the surface of the sperm, primarily over the midpiece, by using an antibody to the canine Na(+)/Ca(2+) exchanger. This antibody recognized a 120-kDa protein that comigrated with the canine myocyte Na(+)/Ca(2+) exchanger. Sperm of Pacific herring are now shown to use reverse Na(+)/Ca(2+) exchange in motility initiation. This mechanism of regulation of motility initiation may have evolved for both maintenance of immotility after spawning as well as ligand-induced motility initiation.

Role of Na(+)-Ca(2+) exchanger after traumatic or hypoxic/ischemic injury to spinal cord white matter

BACKGROUND CONTEXT

Spinal cord injury is a devastating condition in which clinical disability results from demyelination of white matter tracts. Changes in glial-axonal signaling, and enhanced Ca(2+) channel activity with excessive accumulation of intracellular Ca(2+), is a common phenomenon after hypoxia/ischemia or mechanical trauma to spinal cord dorsal column white matter tracts leading to irreversible injury.

PURPOSE

In the present study we examined the role of Na(+)-Ca(2+) exchanger (NCX) at physiological temperatures after hypoxia/ischemia and compressive injury to spinal cord dorsal column white matter in vitro.

STUDY DESIGN

A 30-mm length of dorsal column was isolated from the spinal cord of adult rats, pinned in an in vitro recording chamber (maintained at 37 degrees C) and injured by exposure to a hypoxic atmosphere for 60 minutes or compressed with a modified aneurysm clip (2-gm closing force) for 15 seconds. The functional integrity of the dorsal column was monitored electrophysiologically by quantitatively measuring the compound action potential (CAP) with glass microelectrodes.

RESULTS

The mean CAP decreased to 49.5 +/- 5.7% and 49.4 +/- 2.6% of control (p<.05) after hypoxia/ischemia and compressive injury, respectively. KB-R7943, a potent, selective NCX reverse mode inhibitor, significantly promoted greater recovery of CAP amplitude to 82.0 +/- 10.0% and 70.8 +/- 10.7% of control (p<.05) after hypoxic/ischemic or compressive injury to dorsal column white matter, respectively, when applied at 10 microM concentration. Bepridil (Research Biochemical Inc., Natick, MA, USA) (a less selective NCX inhibitor), when applied at 10 microM and 50 microM concentration promoted CAP amplitude recovery only to 46.8 +/- 7.8% and 29.9 +/- 3.3% of control, respectively, after hypoxic/ischemic injury to dorsal column white matter. Western blot analysis identified NCX presence with positive immunolabeling of 160 kD and 120 kD NCX proteins in the spinal cord white matter.

CONCLUSION

In conclusion, at physiological temperature NCX activation plays an important role in intracellular calcium overload after hypoxic/ischemic and compressive injury to spinal cord dorsal column white matter in vitro.

Inhibitory effect of bepridil on hKv1.5 channel current: comparison with amiodarone and E-4031

Effects of bepridil on the depolarization-activated outward K(+) currents (I(out)) in rat atrial myocytes and the human cardiac K(+) (hKv1.5) channel current stably expressed in human embryonic kidney (HEK) 293 cells were examined, and compared with those of amiodarone and N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl] methanesulphonamide dihydrochloride dihydrate (E-4031). Membrane currents were recorded using patch-clamp techniques in enzymatically isolated rat atrial myocytes and HEK 293 cells expressing hKv1.5 channels. Bepridil potently inhibited I(out) elicited by depolarization pulses and prolonged the action potential in rat atrial cells. Bepridil also inhibited the hKv1.5 channel current with the IC(50) value of 6.6 microM. The inhibitory effects of bepridil on the currents in HEK 293 cells were voltage-dependent. Amiodarone weakly inhibited rat atrial I(out) and hKv1.5 channel current. In contrast, E-4031 at a concentration of 10 microM had little influence on these currents. Thus, bepridil inhibits hKv1.5 channel current and the inhibitory effect may be useful for the treatment of atrial fibrillation.

Synthesis and in vitro studies of pyrone derivatives as scavengers of active oxygen species

The antioxidant properties of eleven alpha-pyrones and four gamma-pyrones were evaluated by means of three different tests: reduction of the stable free radical, 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anion scavenging assay and lipid peroxidation assay. In the DPPH test, 6-aryl-5,6-dihydro-4-hydroxypyran-2-ones (3) and 4-hydroxypyran-2-one (5f) were the most active derivatives with IC50 values ranging from 36.7 to 394 mumol/l. Potent superoxide anion scavenging properties appeared in derivatives possessing phenol moieties. Thus phenolic pyrones 5e and 5f exhibited a noteworthy activity (IC50 = 0.180 and 0.488 mmol/l, respectively) when reference compound, ascorbic acid, demonstrated only 24% inhibition at a concentration of 1 mg/ml. In addition derivative 5f significantly inhibited the Fe2+/ADP/ascorbate-induced lipid peroxidation of rat liver microsomes with an IC50 value of 0.069 mmol/l. Due to its multiple mechanism of protective action, compound 5f may be useful for the treatment of oxidative tissue injury in human disease.

Vasorelaxing and antioxidant constituents from Hernandia nymphaeifolia

Three new alkaloids, (+)-nymphaedaline (1), oxo-O-methylbulbocapnine (2), and (+)-laetine (3), have been isolated from the trunk bark of Hernandia nymphaeifolia. The structures of these new compounds were elucidated by spectroscopic analysis. Among the isolates of this plant obtained till now, sixteen compounds show effective inhibitory activities on the contraction of vascular smooth muscles induced by high K+ (80 mM) or norepinephrine (3 microM). In addition, eight compounds showed effective antioxidant activities in scavenging the stable free radical, diphenyl-picryl-hydrazyl (DPPH).

Superoxide- and 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activities of soyasaponin beta g related to gallic acid

Soyasaponin beta p g at 1 mm had 8% scavenging activity for O2-, and 25 microM beta g scavenged 20.9% for the DPPH radical (IC50: 63.8 microM). In the soyasaponin beta g-gallic acid system, synerigistic effects were observed at a low level of gallic acid concentration. The spin density distribution calculated by the MNDO/AM1 method showed unpaired electron localization on the carbons at C-4 and C-6, and on the ketone group at C-4 of the DDMP moiety. Furthermore, for soyasaponin beta g, the MNDO/AM1 method gave an ionization potential of 8.38 eV, electron affinity of 1.16 eV and Mulliken electronegativity of 4.77 eV. Based on this evidence, the synergistic antiradical effects of the soyasaponin beta g-gallic acid system are assumed to involve two-electron reduction from gallic acid.

Inhibition of Na+/Ca2+ exchange with KB-R7943 or bepridil diminished mineral deposition by osteoblasts

Osteoblasts form new bone by secreting a complex extracellular matrix that has the capacity to mineralize when adequate amounts of calcium and phosphate are supplied. The studies reported here show that long-term treatment of cultured, primary osteoblasts with Na+/Ca2+ exchanger (NCX) inhibitors, bepridil and KB-R7943, impacts in a dose-dependent manner the ability of the cells to form a calcified matrix. Treatment of confluent osteoblast cultures for 14 days with low levels of bepridil (3.0 microM) or KB-R7943 (1.0 microM and 0.1 microM) resulted in a significantly diminished capacity of these cells to mineralize bone matrix, without significantly altering cell morphology, viability, or cell differentiation. The data indicate that inhibition of NCX reduces mineral accumulation in the bone matrix by blocking the efflux of Ca2+ from the osteoblast into the bone fluid. In addition, immunocytochemistry of type I collagen (COLI) and bone sialoprotein (BSP) suggests that inhibition of NCX by 1.0 microM KB-R7943 also may impair the secretion of bone matrix proteins by the osteoblasts. This study is the first to show that NCX is an important regulator of the bone fluid microenvironment and that NCX appears critical to the mineralization process.

Antioxidant principles from Bauhinia tarapotensis

A new cyclohexenone (1) and a new caffeoyl ester derivative (2), together with the known compounds (-)-isolariciresinol 3-alpha-O-beta-D-glucopyranoside (3), (+)-1-hydroxypinoresinol 1-O-beta-D-glucopyranoside (4), isoacteoside (5), luteolin 4'-O-beta-D-glucopyranoside (6), and indole-3-carboxylic acid (7), were isolated from the leaves of Bauhinia tarapotensis. The structures of these new compounds were determined by spectroscopic data analysis. The antioxidant activities of 1-7 were determined by measuring their free radical scavenging effects, using the 1,1-diphenyl-2-dipicrylhydrazyl free radical (DPPH) and Trolox equivalent antioxidant activity (TEAC) methods, and the coupled oxidation of beta-carotene and linoleic acid. Compounds 3-5 showed good activities in the DPPH and TEAC tests, while compounds 1 and 2 were active in the coupled oxidation of beta-carotene and linoleic acid bioassay.

[Bepridil inhibition on the delayed rectifier K+ currents in thyroxine induced hypertrophied guinea pig ventricular myocytes]

AIM

To study the effects of bepridil on the rapidly activating component (IKr), the slowly activating component (IKs) of the delayed rectifier potassium current and the inward rectifier potassium current (IK1) in hypertrophied guinea pig ventricular myocytes.

METHODS

The whole cell patch clamp techniques were used.

RESULTS

In hypertrophied guinea pig ventricular myocytes, bepridil 30 mumol.L-1 markedly inhibited IKr and IKs (by 20.9% and 27.2% at 0 mV and mV, respectively). The effect of bepridil on IKs was larger than on IKr. Bepridil 30 mumol.L-1 also significantly inhibited the inward component of IK1 (by 15.1% at +100 mV), but the reverse potential of IK1 was unaffected. Bepridil (1-100 mumol.L-1) was shown to inhibit IKr and IKs in a concentration-dependent manner. Their IC50 were 46.7 mumol.L-1 and 23.8 mumol.L-1, respectively.

CONCLUSION

Bepridil inhibit IKr, IKs and IK1 in hypertrophied guinea pig ventricular myocytes, which may be important in understanding the antiarrhythmic effects of this drug.