Effects of azelastine on contractility, action potentials and L-type Ca(2+) current in guinea pig cardiac preparations

Mechanisms underlying the cardioprotective effect of Salvianic acid A against isoproterenol-induced myocardial ischemia injury in rats: Possible involvement of L-type calcium channels and myocardial contractility

ETHNOPHARMACOLOGICAL RELEVANCE

Salvianic acid A (SAA), which is the main water-soluble fraction in Radix Salviae Milthiorrhizae, has been widely applied for treating cardiovascular diseases in China.

AIM OF THE STUDY

To explore the effects of SAA against myocardial ischemia injury induced by isoproterenol (ISO) in rats and to clarify its underlying myocardial protective mechanisms based on l-type calcium channels and myocardial contractility.

MATERIALS AND METHODS

The myocardial ischemia injured rat model was induced by administering ISO (85mg/kg) subcutaneously at evenly spaced intervals throughout the day and night for 2 consecutive days. Serum cardiac biomarkers were analyzed, and heart tissues were isolated and prepared for histopathology assay. The regulatory effects of SAA on the L-type calcium current (ICa-L) in rat ventricular myocytes were observed by the patch clamp technique. The IonOptix Myocam detection system was used to observe the contractility of isolated rat ventricular myocytes.

RESULTS

SAA significantly ameliorated changes in heart morphology and electrocardiographic patterns and reduced serum levels of creatine kinase and lactate dehydrogenase in the ISO-induced myocardial ischemia injured rat model. Meanwhile, SAA reduced ICa-L in a concentration-time dependent way with an IC50 of 1.47×10(-5)M, upshifted the current-voltage, activation, and inactivation curves of ICa-L, and significantly inhibited the amplitude of the cell shortening.

CONCLUSIONS

These results indicate that SAA exhibits significant cardioprotective effects against the ISO-induced myocardial ischemia injury, potentially through inhibiting ICa-L and decreasing myocardial contractility.

Effect of azelastine on cardiac repolarization of guinea-pig cardiomyocytes, hERG K⁺ channel, and human L-type and T-type Ca²⁺ channel

Azelastine is a second generation histamine H₁-receptor antagonist used as an anti-asthmatic and anti-allergic drug that can induce QT prolongation and torsades de pointes. We investigated the acute effects of azelastine on human ether-a-go-go-related gene (hERG) channels, action potential duration (APD), and L-type (I(Ca,L)) and T-type Ca²⁺ current (I(Ca,T)) to determine the electrophysiological basis for its proarrhythmic potential. Azelastine increased the APD at 90% of repolarization concentration dependently, with an IC₅₀ of 1.08 nM in guinea-pig ventricular myocytes. We examined the effects of azelastine on the hERG channels expressed in Xenopus oocytes and HEK293 cells using two-microelectrode voltage-clamp and patch-clamp techniques. Azelastine induced a concentration-dependent decrease of the hERG current amplitude at the end of the voltage steps and tail currents. The IC₅₀ for the azelastine-induced block of the hERG currents expressed in HEK293 cells was 11.43 nM, while the drug inhibited I(Ca,L) and I(Ca,T) with IC₅₀ values of 7.60 and 26.21 μM, respectively. The S6 domain mutations, Y652A partially attenuated and F656A abolished hERG current block. These results suggest that azelastine is a potent blocker of hERG channels rather than I(Ca,L) or I(Ca,T), providing molecular mechanisms for the arrhythmogenic side effects during the clinical administration of azelastine.

Effects of Saponin Monomer 13 of Dwarf Lilyturf Tuber on L-Type Calcium Currents in Adult Rat Ventricular Myocytes

The saponin monomer 13 of dwarf lilyturf tuber (DT-13), one of the saponin monomers of dwarf lilyturf tuber, has been found to have potent cardioprotective effects. In order to investigate the effect of DT-13 on L-type calcium currents ( I Ca,L ), exploring the mechanisms of DT-13's cardioprotective effects, we directly measured the I Ca,L in the adult rat cardiac myocytes exposed to DT-13 using standard whole-cell patch-clamp recording technique. Our results showed that DT-13 exerted inhibitory effects on the I Ca,L of the single adult rat cardiac myocytes. The current density was reduced by about 38% after exposure of the cells to DT-13 (0.1 μM) for 10 minutes, from the control value of 7.46 ± 1.31 pA/pF to 4.25 ± 0.35 pA/pF ( n = 6, p < 0.05). This I Ca,L -inhibiting action of DT-13 was concentration-dependent. DT-13 up-shifted the current-voltage (I-V) curve, but did not significantly affect the half activation potential (V0.5). V0.5 was from -11.8 ± 0.9 mV in the control to -12.6 ± 1.9 mV in the presence of DT-13 at 0.1 μmol/L. DT-13 at 0.1 μM did not markedly affect the activation of I Ca,L , but shifted the inactivation curve of I Ca,L to the left. In combination with previous reports, these results suggest that there might be a close relationship between the cardioprotective effects of dwarf lilyturf tuber and the inhibitory effects of DT-13 on L-type calcium currents.

Association of CACNG6 polymorphisms with aspirin-intolerance asthmatics in a Korean population

BACKGROUND

Aspirin-intolerant asthma (AIA) occurs in the lower and upper airways through excessive production of leukotrienes upon administration of non-steroidal anti-inflammatory drugs (NSAIDs). One of the three symptoms of AIA is nasal polyposis, a chronic inflammatory disease that is related to the function of calcium ion in recruitment of immune cells during airway inflammation. It has been implicated that bronchodilation in the airway is related to Ca(2+) regulation. The calcium channel, voltage-dependent, gamma subunit 6 (CACNG6) gene encodes a protein that stabilizes the calcium channel.

METHODS

To study the associations between AIA and polymorphisms in CACNG6 gene, eight variants were genotyped in 102 AIA cases and 429 aspirin-tolerant asthma (ATA) controls. Logistic analyses were used to evaluate the associations of CACNG6 polymorphisms with AIA.

RESULTS

Statistical analyses revealed that a single nucleotide polymorphism (SNP; rs192808C > T; P = 0.0004, Pcorr = 0.0029, OR = 2.88 in co-dominant model; P = 0.0005, Pcorr = 0.0036, OR = 2.99 in dominant model) in intron and a haplotype unique to this variant (CACNG6_BL1_ht6; P = 0.003, Pcorr = 0.02, OR = 2.57 in co-dominant model, P = 0.001, Pcorr = 0.0087, OR = 2.81 in dominant model) were significantly associated with the risk of AIA.

CONCLUSIONS

Our results suggest that the CACNG6 variants might be associated with the risk of AIA in a Korean population.

Inhibition of IgE-mediated phosphorylation of FcεRIγ protein by antiallergic drugs in rat basophilic leukemia (RBL-2H3) cells: A novel action of antiallergic drugs

We examined the effect of antiallergic drugs, azelastine and epinastine, on the expression of FcepsilonRIalpha, beta, and gamma chains and phosphorylation of the gamma chains in rat basophilic leukemia (RBL-2H3) cells. The cells were cultured for 24 h with IgE treatment in the presence of azelastine or epinastine at the concentration of 10(-5) M. The FcepsilonRIalpha mRNA expression was determined by northern blot analysis. The protein level of FcepsilonRI expressed on the plasma membrane was examined following IgE treatment by immunoprecipitation with anti-IgE light chain, followed by western blot analysis with anti-gamma chain of FcR. Azelastine and epinastine had no effect on the FcepsilonRIalpha, beta and gamma mRNA levels. Although the amount of gamma chain assembled into IgE-bound FcepsilonRI was not changed by treatment with azelastine nor epinastine, phosphorylation levels of gamma chains of IgE-bound FcepsilonRI were inhibited by azelastine. The inhibitory effect of azelastine on the IgE-mediated expression of FcepsilonRIgamma protein is not due to their inhibition of mRNA and protein expression, but due to abrogating phosphorylation of the gamma chains, which is important for initiation of FcepsilonRI signaling cascade elicited by IgE interaction.

Antiallergic drugs, azelastine hydrochloride and epinastine hydrochloride, inhibit ongoing IgE secretion of rat IgE-producing hybridoma FE-3 cells

We asked whether or not antiallergic drugs, azelastine hydrochloride and epinastine hydrochloride, inhibit IgE secretion from IgE-producing hybridoma FE-3 cells. FE-3 cells were cultured in the presence of azelastine or epinastine for 24 h, washed in phosphate-buffered saline , and then recultured in the medium in the absence of the antiallergic drugs. IgE levels in the cultured medium as well as those in the cytoplasm of FE-3 cells were measured by enzyme-linked immunosorbent assay. mRNA levels of Cepsilon, activation-induced cytidine deaminase (AID), XBP-1, and Bip were estimated by northern blot or reverse transcriptase polymerase chain reaction analysis. The activities of nuclear factor-kappa B (NF-kappaB) were analyzed by electrophoretic mobility shift assay (EMSA). Phosphorylation of I kappa B alpha (IkappaBalpha) was analyzed by immunoprecipitation followed by western blot analysis. IgE levels in the cultured medium and in the microsome fraction were lower on the treatment with 10(-5) M azelastine or epinastine than those on the treatment with vehicle. Cepsilon and AID mRNA levels were lower on the treatment with 10(-5) M azelastine than those on the treatment with vehicle, but were not decreased on the treatment with 10(-5) M epinastine. XBP-1 and Bip mRNA levels were not altered following treatment of the antiallergic drugs. Azelastine at 10(-5) M, but not epinastine, reduced DNA binding activity of NF-kappaB and also diminished IkappaBalpha phosphorylation, leading to sustaining IkappaBalpha protein levels. These findings suggest that azelastine exerts its inhibitory effect on the IgE secretion from FE-3 cells through the inhibition of Cepsilon mRNA expression, and that the inhibitory effect of epinastine is, at least in part, due to suppression of IgE synthesis at the post-transcriptional level.

Trimetazidine improved Ca2+ handling in isoprenaline-mediated myocardial injury of rats

Dysregulation of intracellular Ca2+ homeostasis plays an important role in mediating myocardial injury. We tested the hypothesis that treatment with trimetazidine (TMZ) would improve intracellular Ca2+ handling in myocardial injury of rats. The control group received saline only (10 ml kg(-1) day(-1), i.p.) for 7 days. In a second group, isoprenaline (ISO; 5 mg kg(-1) day(-1), s.c.) was administered to rats for 2 days to induce an acute injury of the myocardium. In a third group, treatment with TMZ (10 mg kg(-1) day(-1), i.p.) was initiated 1 day before ISO administration and continued for 7 days (n = 7 rats in each group). Histopathological evaluation showed that TMZ prevented ISO-induced myocardial damage. TMZ preserved the ATP levels and decreased the maleic dialdehyde (MDA) content in the hearts compared with ISO-treated rats. The diastolic [Ca2+]i measured by loading with fura-2 AM in isolated cardiomyocytes was increased significantly in ISO-treated rats compared to the control animals. TMZ prevented the rise of diastolic [Ca2+]i and the depression of caffeine-induced Ca2+ transients caused by ISO administration. The reduction in sarcoplasmic reticulum (SR) Ca2+ content in the heart cells and in cardiac SR Ca2+-ATPase activity in ISO-treated rats was abolished by TMZ, although there were no differences in SR Ca2+-ATPase protein levels between the control, ISO and ISO + 7 mz-treated rats. In addition, TMZ prevented the reduction in sarcolemmal L-type Ca2+ current density in the heart cells induced by ISO treatment. These results demonstrate that the treatment of rats with TMZ inhibited the increase of diastolic [Ca2+]i and prevented the decrease of SR Ca2+ content, SR Ca2+-ATPase activity and L-type Ca2+ current density in cardiomyocytes in ISO-mediated myocardial injury of rats. These changes in Ca2+ handling could help to explain the favourable action of TMZ in myocardial injury.

Urocortin II Inhibits the Apoptosis of Mesenteric Arterial Smooth Muscle Cells Via L-type Calcium Channels in Spontaneously Hypertensive Rats

Urocortin (UCN) II, a newly isolated corticotropinreleasing- factor (CRF) related peptide, has been found to have potent cardiovascular protective effects. To investigate the mechanisms of its vascular protective effects, we exposed mesenteric arterial smooth muscle cells (MASMC) from spontaneously hypertensive rats (SHR) to UCN II to observe the change in cell apoptosis using TUNEL assay and measured intracellular calcium concentration ([Ca2+]i) using confocal laser scanning microscope. In addition, effects of UCN II on L-type calcium currents (ICa,L) were also measured using whole-cell patch clamp. Our results showed that UCN II concentration-dependently, but time-independently inhibited cell apoptosis. Astressin 2B, a special CRF 2 receptor antagonist, had no influence on this inhibition. Hypoxia or Bay K8644, the L-type calcium channel activator, induced the apoptosis of MASMC from SHR. Pretreatment of the cells with UCN II diminished the effects of hypoxia or Bay K8644. UCN II was also observed to reduce [Ca2+]i increase induced by KCl or Bay K8644. UCN II concentration-dependently inhibited ICa,L, which was not affected by astressin 2B. It did not affect the activation of ICa,L, but markedly shifted the inactivation curve to the left. In conclusion, UCN II inhibits the apoptosis of MASMC from SHR via inhibiting L-type calcium channels.

The saponin monomer of dwarf lilyturf tuber, DT-13, reduces L-type calcium currents during hypoxia in adult rat ventricular myocytes

The saponin monomer 13 of dwarf lilyturf tuber (DT-13), one of the saponin monomers of dwarf lilyturf tuber, has been found to have potent cardioprotective effects. In order to investigate the effects of DT-13 on L-type calcium currents (I(Ca,L)), exploring the mechanisms of DT-13's cardioprotective effects in the condition of pathophysiology, we directly measured the I(Ca,L) during hypoxia in the adult rat cardiac myocytes exposed to DT-13 using standard whole-cell patch-clamp recording technique. Our previous results showed that DT-13 exerted decreasing effects on the I(Ca,L) of the single adult rat cardiac myocytes. In the condition of hypoxia, the current density was inhibited by about 29% after exposure of the cells to DT-13 (0.1 micromol L(-1)) for 10 min, from 6.96+/-1.05 pA/pF to 4.38+/-0.35 pA/pF (n=5, P<0.05). This I(Ca,L)-inhibiting action of DT-13 was concentration-dependent and showed no frequency-dependence. DT-13 up-shifted the current-voltage (I-V) curve. Steady-state activation of I(Ca,L) was not affected markedly, and the half activation potential (V(0.5)) in the presence of DT-13 (0.1 micromol L(-1)) was also not significantly different. DT-13 at 0.1 micromol L(-1) markedly accelerated the voltage-dependent steady-state inactivation of calcium current and shifted the steady-state inactivation curve of I(Ca,L) to the left. In combination with previous reports, these results suggest that there might be a close relationship between the cardioprotective effects of DT-13 and L-type calcium channels in the condition of hypoxia.

Effect of urocortin on L-type calcium currents in adult rat ventricular myocytes

The newly isolated peptide, urocortin (UCN) has been found to have potent cardioprotective effects. In order to investigate the effect of UCN on L-type calcium currents (I(Ca,L)), exploring the mechanisms of UCN's cardioprotective effects, we directly measured the I(Ca,L) in the adult rat cardiac myocytes exposed to UCN using standard whole-cell patch-clamp recording technique. Our results showed that UCN exerted decreasing effects on the I(Ca,L) of the single adult rat cardiac myocytes. The current density was inhibited by about 35% after exposure of the cells to UCN (0.1 micromol L(-1)) for 10 min, from the control value of 7.19 +/- 1.44 pA/pF to 4.74 +/- 0.75 pA/pF (n = 5, P < 0.05). This I(Ca,L)-inhibiting action of UCN was concentration dependent. Moreover, no frequency dependence of UCN effects on I(Ca,L) was observed. In combination with previous reports, our results suggest that there might be a close relationship between the cardioprotective effects of UCN and L-type calcium channels.