ABSTRACT
Sodium salicylate is an anti-inflammatory medication with a side-effect of tinnitus. Here, we used mouse cochlear cultures to explore the effects of salicylate treatment on cochlear inner hair cells (IHCs). We found that IHCs showed significant damage after exposure to a high concentration of salicylate. Whole-cell patch clamp recordings showed that 1-5 mmol/L salicylate did not affect the exocytosis of IHCs, indicating that IHCs are not involved in tinnitus generation by enhancing their neuronal input. Instead, salicylate induced a larger peak amplitude, a more negative half-activation voltage, and a steeper slope factor of Ca2+ current. Using noise analysis of Ca2+ tail currents and qRT-PCR, we further found that salicylate increased the number of Ca2+ channels along with CaV1.3 expression. All these changes could act synergistically to enhance the Ca2+ influx into IHCs. Inhibition of intracellular Ca2+ overload significantly attenuated IHC death after 10 mmol/L salicylate treatment. These results implicate a cellular mechanism for tinnitus generation in the peripheral auditory system.
Subject(s)
Animals , Mice , Calcium , Exocytosis , Hair Cells, Auditory, Inner , Sodium Salicylate/pharmacology , Tinnitus/chemically inducedABSTRACT
Bombesin receptor subtype-3(BRS-3) is an orphan receptor in the bombesin receptor family. Its signal transduction mechanism and biological function have attracted much attention. Seeking the ligand for BRS-3 is of great significance for exploring its function. Considering the fact that the activation of BRS-3 receptor can induce the change in intracellular Ca~(2+) concentration, the fluo-rometric imaging plate reader(FLIPR) was utilized for ligand screening at the cellular level. Among more than 400 monomeric compounds isolated from Chinese herbs, yuanhunine from Corydalis Rhizoma and sophoraisoflavanone A and licoriphenone from Glycyrrhizae Radix et Rhizoma antagonized BRS-3 to varying degrees. It was confirmed in HEK293 cells expressing BRS-3 that yuanhunine, sophoraisoflavanone A, and licoriphenone inhibited the calcium current response after the activation of BRS-3 by [D-Phe~6,β-Ala~(11),Phe~(13),Nle~(14)]bombesin-(6-14) in a dose-dependent manner with the IC_(50) values being 8.58, 4.10, and 2.04 μmol·L~(-1), respectively. Further study indicated that yuanhunine and sophoraisoflavanone A exhibited good selectivity for BRS-3. In this study, it was found for the first time that monomers derived from Chinese herbs had antagonistic activity against orphan receptor BRS-3, which has provided a tool for further study of BRS-3 and also the potential lead compounds for new drug discovery. At the same time, it provides reference for the research and development of innovative drugs based on the active ingredients of Chinese herbs.
Subject(s)
Humans , Drugs, Chinese Herbal/chemistry , HEK293 Cells , Ligands , Receptors, BombesinABSTRACT
Objective To observe the effect of allicin on the action potential duration (APD) and L-type calcium current (ICa,L) in the ventricular myocytes of rabbits with heart failure in order to explore the mechanisms of therapeutic effect of allicin on cardiac arrhythmias complicated with heart failure.Methods Forty-five New Zealand White male rabbits were randomly (random number) assigned to 3 groups (n=15 in each group):sham operated group (sham group),heart failure group (HF group),and heart failure treated with allicin group (HF+All group).The rabbit heart failure model was established by abdominal aortic constriction coupled with aortic regurgitation,the ventricular myocytes were obtained by enzyme double digestion,and the whole cell clamp was used to record action potential and calcium current.The action potential duration (APD),Ica,L and gating mechanism were observed during heart failure and allicin administered.Data were processed with pCLAMP version 10.2.Statistical analysis was performed using SPSS 17.0.Comparisons among groups were carried out using ANOVA,and SNK-q was used for multiple comparison as post-hoe.Results (1) Prolonged APD was found during heart failure,APD50 was prolonged from (93.4±4.7) ms in sham group to (115.5±6.2) ms in HF group(P＜0.01).After administration of allicin 30 μmol/L,APD50 was shortened to (105.2±5.5) ms (P＜0.05).(2) The density of ICa.L increased during heart failure,peak current density increased increased from (-8.4±0.6) pA/pF in sham group to (-15.1± 1.1) pA/pF while 0 mV attained at depolarizations (P＜0.01).After administration of allicin 30 μmol/L,the current density reduced to (-10.1+0.8) pA/pF (P＜0.01).The effect of allicin presented in both voltage dependent and consentration dependent manner.(3) According to the gating mechanism study,the main mechanism of lowering the density of ICa,L by allicin after heart failure was the acceleration of the steady inactivation of the channel,and the de-escalation of the recovery kinetic after the inactivation of the channel.Conclusions Allcin can be used to reduce the calcium current of ventricular myocytes in animal heart failure model,it has the potential of clinical use in treating cardiac arrhythmias during heart failure.
ABSTRACT
[ ABSTRACT] AIM:To establish a perforated whole-cell patch-clamp technique withβ-escin to record L-type cal-cium current (ICa,L) in osteoblasts.METHODS:ROS 17/2.8 is a rat osteoblast-like osteosarcoma cell line.β-escin was applied to the pipette solution to permeabilize the cell membrane and the perforated patch recording mode was obtained. RESULTS:β-escin at concentration of 50μmol/L easily permeabilized the cell membrane and obtained a perforated patch recording mode in 2~7 min.This technique prevented ICa,L rundown and preserved cytoplasmic signaling pathways.CON-CLUSION:β-escin may be used as an alternative ionophore for perforated patch-clamp studies in osteoblasts and results in minimal rundown that could facilitate recordings of ICa,L in osteoblasts.
ABSTRACT
Objective: To observe the effect of cilostazol on the ion channel of right ventricular cells in experimental rats, and to explore the ion channel mechanism of ciolstazol for preventing the ventricular arrhythmia in Brugada syndrome. Methods: Our research was composed of 2 groups: ①Perfusion group, the cells were treated in 4 sub-groups by cilostazole at 1, 2, 5, 50μmol/L respectively, and there were 9, 5, 3, 7 cells were recorded at each sub-group to observe the differences of current density Ito at before and after treatment. ②Oral group, which included 4 sub-groups:Control 1 with 7 rats, Experiment 1 with 5 rats, and Control 2 with 8 rats, Experiment 2 with 6 rats respectively. The differences of current density Ito and ICa,L were studied between each Control and Experiment sub-groups. Results: In Perfusion group,①with cilostazole 1, 2, 5, 50μmol/L treatment, the current density Ito decreased in all sub-groups, when the self-command voltage at+60mV, the Ito was signiifcantly different in each sub-group at before and after treatment, all P0.05. In Oral group,①When the self-command voltage from-50mV reached the maximum of+60mV, the Ito was similar between Control 1 and Experiment 1 sub-groups, P>0.05.②When the self-command voltage at+10mV, the current density of ICa,L was slightly higher in Control 2 sub-group than that in Experiment 2 sub-group, P>0.05. Conclusion: Direct perfusion of cilostazole in right ventricular cells may inhibit Ito in experimental rats, such effect was similar with cilostazole treatment at (1-50)μmol/L. Cilostazole might prevent the ventricular arrhythmia in Brugada syndrome in experimental rats.
ABSTRACT
Objective To investigate the effect of the calmodulin kinase Ⅱ Inhibitor KN-93 on L-typecalcium current(ICa,L)and intracellular calcium concentration([Ca2+]i)in hypertrophic cardiac myocytes.Methods Forty-eight female New Zealand white rabbits were randomized(random number)into four groups(12 animals in each group):the sham operation group(sham group),the left ventricular hypertrophy group(LVH group),the myocardial hypertrophy + KN-93 group(KN-93 group),and the myocardial hypertrophy + KN-92 group(KN-92 group).Myocardial hypertrophy in the rabbits was established by coarctation of the abdominal aorta.In the sham group,the abdominal aorta was dissociated without coarctation.Eight weeks after coarctation,single ventricular myocytes were isolated by enzymaticdissociation,and ICa,L was recorded using perforated-patch recording(PPR)techniques.[Ca2+]i was measured using single-cell calcium imaging with the fluorescence calcium indicator dye fura-2/AM.Results Cardiac hypertrophy was successfully established after 8 weeks of coarctation of the abdominal aorta.The peak ICa,L in the LVH group and the sham group was(1.38 ± 0.3)nA and(0.87 ± 0.1)nA at 0 mV,respectively(P ＜0.01,n =12).There was no significant difference in Ica,L density between the LVH group and the sham group[(6.7 ±1.0)pA/pF vs.(6.3±0.7)pA/pF; P≥0.05,n=12].The addition of either KN-92(0.5 μmol/L)or KN-93(0.5 μmol/L)to the perfusing solution caused a modest steady-state inhibition of peak ICaL(9.4％ ±2.8％,KN-92; 10.5％ ±3％,KN-93)(P≥0.05,n =12)at 0 mV.However,at a higher concentration(1 μmol/L),KN-93 more potently inhibited peak ICa,L(40％±4.9％)compared to KN-92(13.4％ ± 3.7％ ; P ＜ 0.01,n =12).Resting[Ca2+]i levels in fura-2-loaded myocytes isolated from the sham,LVH,KN-92,and KN-93 groups were(98 ± 12.3)nmol/L,(154 ± 26.2)nmol/L,(147 ± 29.6)nmol/L,and(108 ± 21.2)nmol/L,respectively.Conclusions The CaMK Ⅱ specific inhibitor,KN-93,can effectively block ICa,L and reduce intracellular calcium overload in hypertrophic cardiac myocytes.This action may account for the antiarrhythmic effect of KN-93 in hypertrophic ventricular myocardium.
ABSTRACT
Objective To assess the anti-arrhythmic activity and cardioprotective effects of Wenxin Granula, a traditional Chinese formula (consisting of Salviae Miltiorrhizae Radix, Polygonati Rhizoma, Notoginseng Radix et Rhizoma, Nardostachyos Radix et Rhizoma, Angelicae Sinensis Radix, and Succinum), on heart in ischemic-induced myocardial infarction (MI) rats and compare with those of Amiodarone which have been demonstrated in clinic. Methods Rats were randomly divided into Sham-operated (control), Ml + Amiodarone [5 mg/(kg·d)] (MI), and MI + Wenxin Granula [10 mg/(kg·d)] groups and left anterior descending coronary artery was occluded in each group. After left anterior descending for 12 h, standard lead Ⅱ of administration electrocardiogram was recorded in order to analyze the occurrence of arrhythmia. After one month, the size of the infarct area of heart was evaluated by TTC staining method and haemodynamic function was assessed to detect the heart function. Laser scanning confocal microscope and the technique of patch clamp were used to detect the intracellular Ca2+ ([Ca2+]j) and L-type calcium current (ICa-L), respectively. Results Both Wenxin Granula [10 mg/(kg·d)] and Amiodarone [5 mg/(kg·d)] could markedly decrease the incidence of arrhythmia in heart of rats which were subjected to ischemic injury. After one month, Wenxin Granula could significantly decrease mortality to 22.22% and reduce the infarct area (P < 0.05), but Amiodarone did not. The mechanism may involve that Wenxin Granula attenuated [Ca2+]j decreasing in MI rats. Additionally, Wenxin Granula could obviously ameliorate the impaired heart function of MI rats by decreasing the elevated left ventricular end-diastolic pressure and increasing the attenuated maximum change velocity of left ventricular pressure in the isovolumic contraction or relaxation period. On the other hand, electrophysiological experiment results revealed that Wenxin Granula administration one month later also increased the reduced ICa-L density in rat ventricular myocytes in MI rats. The results of LSCM showed that Wenxin Granula could recover the amplitude of [Ca2+]j decreased by heart failure during long term. Conclusion Wenxin Granula could not only inhibit the incidence of arrhythmia but also decrease the mortality, which was accompanied by recovering the amplitude of [Ca2+]j. This protective effect of Wenxin Granula may partially be mediated through changing ICa-L.as well as increasing [Ca2+]j.
ABSTRACT
Aim To observe the effect of Ginkgo biloba extract 50(GBE50)on L-type calcium current and cytosolic[Ca~(2+)]_i in ischemic guinea pig ventricular myocytes.Methods Single ventricular myocytes were isolated by enzymatic dissociation. I Ca-L was recorded by whole-cell patch clamp technique in voltage clamp mode.[Ca~(2+)]_i was detected by laser confocal micros-copy and represented by relative fluorescent intensity (FI).Results During ischemia, the peak Ca~(2+) current was reduced, and the I-U curve of I Ca-L was shifted upward.50 mg·L~(-1) GBE50 reversed the change induced by ischemia(n =6, P >0.05).After perfusing ischemic solution for 12 min, intracellular calcium concentration was increased(n =10, P <0.01).After perfusion with ischemic solution containing 50 mg·L~(-1) GBE50, the increase of intracellular calcium concentration was markedly inhibited(n =10, P >0.05).Conclusion GBE50 can reverse the decrease of I Ca-L and partially inhibit calcium overloading during ischemia.
ABSTRACT
AIM: To evaluate the effects of simulated acute ischemia and reperfusion on L-type calcium current (ICa,L) in ventricular myocytes from diabetic and non-diabetic rabbits.METHODS: Using whole-cell patch clamp techniques, ICa,L was measured in left ventricular myocytes isolated from 6-week alloxan-induced diabetic rabbits and age-matched control ones at baseline, 5 min of simulated ischemia, and 5 min of reperfusion.RESULTS: There were no significant differences on baseline maximum ICa,L densities between diabetic and control ventricular myocytes. In control cells (n=11), maximal ICa,L densities of baseline, ischemia and reperfusion were (-8.36±1.63)pA/pF, (-5.90±1.75)pA/pF and (-4.22±1.02)pA/pF, respectively. The ICa,L of ischemia was less than that of baseline (P<0.01), while the ICa,L of reperfusion was less than those of baseline (P<0.01) and ischemia (P<0.05). In diabetic cells (n=9),the ICa,L of baseline, ischemia and reperfusion were (-7.55±1.62)pA/pF, (-6.05±1.58)pA/pF and (-5.12±1.13)pA/pF, respectively. Only ICa,L of reperfusion was less than that of baseline (P<0.01), while ICa,L of ischemia was not significantly different from that of baseline (P>0.05) or reperfusion (P>0.05).CONCLUSION: ICa,L in diabetic ventricular myocytes represents blunted response to acute ischemic injury, being decreased more slowly than that in control cells. Post-ischemic reperfusion is still a potent inhibitor against ICa,L in both diabetic and non-diabetic cells. This study may be indicative of the mechanism about ischemia-reperfusion injury to diabetic myocardium and the therapy for diabetic patients with ischemic heart disease.
ABSTRACT
Objective To determine the effects of valsartan, a specific angiotensin Ⅱ type 1 receptor blockade, on arrhythmia in rabbits after myocardial infarction and to discuss the mechanism. Method Twentyfour rabbits were randomly (random number) divided into sham operated (SO) group ( n = 8), myocardial infarction (MI) group ( n = 8) and valsartan (VAL) group ( n = 8). The rabbits of SO group were operated upon with median stemotomy without left ventricular coronary artery hgature. The rabbits of MI group and VAL group had median stemotomy with left ventricular coronary artery ligature. After MI, the rabbits of VAL group were fed with border zone of infracted left ventricular wall and the L-type calcium current was recorded by whole-cell patch clamp technique. Results Ventricular tachycardia or fibrillation (VT/VF) episodes were markedly decreased in VAL group than that in MI group [(3.2 ± 0. 6) vs. ( 11.7 ± 1.8)] after 12 weeks. The density of Ica-L current was higher in MI group than that in SO group and VAL group [( - 9.12 ± 0.73) pA/pF vs. ( - 6.29 ± 0.65) pA/pF and ( - 6.75 ± 0.64) pA/pF], ( P ＜ 0.05), however, there were no significant differences in Ica-L current between So group and VAL group ( P ＞ 0.05). Conclusions Valsartan reduces the VT/VF episodes in rabbits after MI. The effects of valsartan may be attributed to the inhibited electrical remodeling after MI.
ABSTRACT
To elucidate the mechanism of cyclic nucleotides, such as adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5' -cyclic monophosphate (cGMP), in the regulation of human gastric motility, we examined the effects of forskolin (FSK), isoproterenol (ISO) and sodium nitroprusside (SNP) on the spontaneous, high K+ and acetylcholine (ACh)-induced contractions of corporal circular smooth muscle in human stomach. Gastric circular smooth muscle showed regular spontaneous contraction, and FSK, ISO and SNP inhibited its phasic contraction and basal tone in a concentration-dependent manner. High K+ (50 mM) produced sustained tonic contraction, and ACh (10 micrometer) produced initial transient contraction followed by later sustained tonic contraction with superimposed phasic contractions. FSK, ISO and SNP inhibited high K+-induced tonic contraction and also ACh-induced phasic and tonic contraction in a reversible manner. Nifedipine (1 micrometer), inhibitor of voltage-dependent L-type calcium current (VDCC(L)), almost abolished ACh-induced phasic contractions. These findings suggest that FSK, ISO and SNP, which are known cyclic nucleotide stimulators, inhibit smooth muscle contraction in human stomach partly via inhibition of VDCCL.
Subject(s)
Humans , Acetylcholine , Adenosine , Calcium , Contracts , Colforsin , Guanosine , Isoproterenol , Muscle, Smooth , Nifedipine , Nitroprusside , Nucleotides, Cyclic , Relaxation , StomachABSTRACT
It was previously showed that aqueous leaf extract (AqEx) of Averrhoa carambola depresses the guinea pig atrial inotropism. Therefore, experiments were carried out on guineapig left atrium and on pituitary GH3 cells in order to evaluate the effect of AqEx on the cellular calcium infl ux. The atrium was mounted in an organ chamber (5 mL, Tyrode, 27 ± 0.1 °C, 95% O2, 5 % CO2), stretched to 10 mN, and paced at 2 Hz (0.5 ms, 400 V) and GH3 cells were submitted to a whole cell voltage clamp confi guration. In the atrium, the AqEx (1500 μg/mL) shifted to the right the concentration-effect curve of the positive inotropic effect produced by (±) BAY K 8644, an L-type calcium channel agonist. The AqEx increased EC50 (concentration required to promote 50% of the maximum effect) of the inotropic effect of BAY K 8644 from 7.8 ± 0.38 to 115.1 ± 0.44 nM (N = 3; p < 0.05). In GH3 cells assayed with 500 μg/mL of AqEx, the L-type calcium inward current declined 30 % (from 282 to 190 pA). Nevertheless, the extract did not change the voltage correspondent to the peak current. These data suggest that, at least in part, the negative inotropic effect of AqEx on the guinea pig atrium is due to a reduction of the L-type calcium current.
Em estudo prévio mostrou-se que o extrato aquoso das folhas de Averrhoacarambola (ExAq) reduziu o inotropismo atrial da cobaia. Por isso, este trabalho avaliou se o ExAq interfere com o infl uxo de cálcio através da membrana celular. A investigação foi conduzidaem átrio esquerdo de cobaia, montado em cuba (5 mL, Tyrode, 27 ± 0,1 °C, 95 % O2, 5 % CO2), estirado para uma tensão de repouso de 10 mN e submetido a uma estimulação de 2 Hz (0,5 ms, 400 V). O efeito do ExAq sobre a entrada de cálcio nas células foi avaliado em átrio de cobaia e em células GH3, estas submetidas a patch clamp na confi guração whole cell. No átrio, o ExAq (1500 μg /mL) deslocou para direita a curva concentração-efeito do (±) BAY K 8644 (agonista dos canais de cálcio tipo-L), aumentando a CE50 (concentração capaz de produzir 50 % do efeito máximo) de 7,8 ± 0,38 para 115,1 ± 0,44 nM (N = 3, p < 0,05). Em células GH3, este extrato (500 μg /mL) reduziu de 282 para 190 pA (30 %) a corrente de cálcio, sem contudo alterar a voltagem de pico da curva desta corrente. Estes resultados mostram que, pelo menos em parte, o efeito inotrópico negativo do ExAq em átrio de cobaia se deve a uma diminuição do infl uxo de cálcio pelos canais tipo-L.
ABSTRACT
Objective To study the intervention effect of tanshinone on electrophysiological abnormality of hypertrophic cardicoyte in order to illuminate the underlying mechanism of tanshinone in preventing the arrhythmia induced by myocardial hypertrophy. Method Twenty-week-rid SD rats (200～250 g) were divided into 4 groups (8 in each group) randomly. Of 4 groups, rats of three groups were operated on by a procedure of 'one kidney one clamp' to make renal artery constriction. The rest group served as sham operation group (control group). When the blood pressure increased,rats of operation groups were divided into tanshinone group, captopril group and hyper-trophic group. The effects of tanshinoe and captopril were observed and compared on the action potential duration (APD),L-type calcium current (ICa, L) and transient outward potassium current (Ito) density in cellular membrane of hypertrophic myocardium by using patch clamp and intra-cellular calcium survey technique. Results The blood pressure in operation groups was obviously higher than that in sham-operation group (P<0.01), but there was no difference between operation groups (P>0.05). The ratio of ventricle weight to body weight (VW/BW) was much higher in hypertrophic group than in control group (P<0.01), and it significantly decreased after interven-tion with tanshinone or captopril (P<0.01). Compared with hypertrophic group, tanshinone markedly shortened the prolongation of action potential duration (P<0.01), decreased membrane capacity and peak amplitude of ICa,L(P<0.01), but had no effect on the density of ICa,L. Tanshinone also significantly increased Ito current density and peak amplitude, which were completely different from hypertrophic group (P<0.05). There were similar results foundin captopril intervention. Conclusions Tanshinone could reduce calcium influx and resume the activity of ho ion channels, and thus shorten the first phase and the plateau phase of repolarization and decrease the prolongation of APD in hypertrophic cadiocyte. So tanshinone can prevent the onset of arrhythmia attributed to the myocardial hypertrophy.
ABSTRACT
In our previous study, we found that spermine and putrescine inhibited spontaneous and acetylcholine (ACh)-induced contractions of guinea-pig stomach via inhibition of L-type voltage- dependent calcium current (VDCCL). In this study, we also studied the effect of spermidine on mechanical contractions and calcium channel current (IBa), and then compared its effects to those by spermine and putrescine. Spermidine inhibited spontaneous contraction of the gastric smooth muscle in a concentration-dependent manner (IC50=1.1+/-0.11 mM). Relationship between inhibition of contraction and calcium current by spermidine was studied using 50 mM high K+-induced contraction: Spermidine (5 mM) significantly reduced high K+(50 mM)-induced contraction to 37+/-4.7% of the control (p<0.05), and inhibitory effect of spermidine on IBa was also observed at a wide range of test potential in current/voltage (I/V) relationship. Pre- and post-application of spermidine (5 mM) also significantly inhibited carbachol (CCh) and ACh-induced initial and phasic contractions. Finally, caffeine (10 mM)-induced contraction which is activated by Ca2+-induced Ca2+release (CICR),` was also inhibited by pretreatment of spermidine (5 mM). These findings suggest that spermidine inhibits spontaneous and CCh-induced contraction via inhibition of VDCCL and Ca2+releasing mechanism in guinea-pig stomach.
Subject(s)
Acetylcholine , Caffeine , Calcium , Calcium Channels , Carbachol , Contracts , Muscle, Smooth , Putrescine , Relaxation , Spermidine , Spermine , StomachABSTRACT
AIM: To determine whether chronic hypercholesterolemia affects ionic currents on cardiac ventricular myocytes of rats. METHODS: Whole - cell patch - clamp technique was used to record the ionic currents in single cardiac myocytes isolated from normal cholesterolemia and hypercholesterolemia rats. RESULTS: In the hypercholesterol group (group Ⅱ ), serum total - cholesterol level was significantly higher than that of normal group (group Ⅰ) [ (3. 10 ±tricular myocytes of rats, 50% repolarization of action potential duration (APD50) prolonged from (70. 86 ± 8.12) ms (group Ⅰ) to (116.16±6.90)ms (group Ⅱ) (n=10 in each group, P＜0.01); APD90 prolonged from (95.10±7. 27)ms (group Ⅰ ) to (144. 04 ± 7.39)ms (group Ⅱ ) (n = 10 in each group, P ＜ 0. 01 ); at the test potential of - 120 mV, Ik1 increased from ( - 16. 98 ±4. 54) pA/pF(group Ⅰ ) to ( - 19.92 ±4.08) pA/pF (group Ⅱ ) (n = 12 in each group, P ＜ 0. 05 ); at the test potential of 0 mV, ICa- L decreased from ( - 8.56 ± 1.29) pA/pF ( group Ⅰ ) to ( -5. 24 ± 0. 90) pA/pF ( group Ⅱ ) ( n = 10 in each group, P ＜ 0. 01 ); at the test potential of + 60 mV, Ito decreased from (13.20±1.97) pA/pF (group Ⅰ) to (10.30±1.97) pA/pF (group Ⅱ) (n=8 in each group, P＜0. 05). CON-CLUSION: Hypercholesterolemia affects the ionic currents on cardiomyocytes of rats greatly, which may be the ionic mechanism of cardiac toxicity induced by hypercholesterolemia.
ABSTRACT
This study was designed to investigate the effects of polyamines on mechanical contraction and voltage-dependent calcium current (VDCC) of guinea-pig gastric smooth muscle. Mechanical contraction and calcium channel current (I(Ba)) were recorded by isometric tension recording and whole-cell patch clamp technique. Spermine, spermidine and putrescine inhibited spontaneous contraction of the gastric smooth muscle in a concentration-dependent manner. Spermine (2 mM) reduced high K+ (50 mM)-induced contraction to 16+/-6.4% of the control (n=9), and significantly inhibited I(Ba) in a reversible manner (p<0.05; IC50=0.8 mM). Pre- and post-treatment of tissue with spermine (2-5 mM, n=10) also inhibited acetylcholine (10 micrometer)-induced phasic contraction to 5+/-6.4% of the control. Inhibitory effect of spermine on I(Ba) was observed at a wide range of test potentials of current/voltage (I/V) relationship (p<0.05), and steady-state activation of I(Ba) was shifted to the right by spermine (p<0.05). Spermidine and putrescine (1 mM each) also inhibited I(Ba) to 51+/-5.7% and 81+/-5.3% of the control, respectively. And putrescine (1 mM) inhibited I(Ba) at whole tested potentials (p<0.05) without significant change of kinetics (p<0.05). Finally, 5 mM putrescine also inhibited high K+ -induced contraction to 53+/-7.1% of the control (n=4). These findings suggest that polyamines inhibit contractions of guinea-pig gastric smooth muscle via inhibition of VDCC.
Subject(s)
Male , Female , Animals , Pyloric Antrum/drug effects , Potassium/pharmacology , Polyamines/pharmacology , Muscle, Smooth/drug effects , Muscle Contraction/drug effects , Guinea Pigs , Calcium Channels/drug effects , Calcium/metabolismABSTRACT
@#ObjectiveTo investigate the effect of hyperlipidemia on monophasic action potential and calcium current of heart in rabbits.Methods24 rabbits were divided into the high cholesterol group (n=12) and control group (n=12) and fed with high cholesterol forage and standard forage respectively for 10 weeks. Electrocardiograph, ventricular fibrillation threshold and the level of serum lipid were examined. Whole-cell patch clamp technique was used to record I_ Ca-L.ResultsIn high cholesterol group, the serum cholesterol level was higher than the control group ( P<0.01), ventricular fibrillation threshold (10.2±1.7 V) lower than that of the control group (13.9±1.3 V)( P<0.05), MAPD90 displayed more significant rate-dependent prolongation. At cycle lengths of 1500 ms, MAPD90 was 358±18 ms in the high cholesterol group, while it was 277±20 ms in the control group. The densities of ICa-L were larger in the high cholesterol group (14.7±0.8 pA/pF) than that in the control group (10.9±1.1 pA/pF)( P<0.01).ConclusionHypercholesterolemia can produce cardiac electrical remodeling, including increased ICa-L, prolonged repolarization and decreased ventricular fibrillation thresholds.
ABSTRACT
Summary: The current difference between male and female rabbit ventricular myocytes was investigated for elucidating the mechanism of longer QT interval and higher incidence of drug-associated torsade de pointes in female rabbits than in male rabbits. Whole cell patch clamp technique was used to record APD, Ito, IK,tail, IK1 and ICa,L of myocytes from left ventricular apex. There was no difference in the membrane capacitance between male and female rabbit myocytes. APD90 was longer in female rabbits (560.4±26.5 ms, n=15) than in male ones (489.0±20.7 ms, n=14), P<0.05. In female rabbit myocytes, IK,tail, Ito, IK1 and ICa,L were 0.71±0.05 pA/pF (n=17), 8.28±1.03 pA/pF (n=18), 24.5±3.6 pA/pF (n=12) and 9.0±2.3 pA/pF (n=15) respectively. In male rabbit myocytes, they were 0.84±0.07 pA/pF (n=18), 8.60±1.20 pA/pF (n=18), 25.9±4.5 pA/pF (n=14) and 9.3±2.6 pA/pF (n=16) respectively. IK,tail in female rabbits was significantly lower than that of male rabbits (P<0.05), but there was no difference in Ito, IK1 and ICa,L between male rabbits and female rabbits (P>0.05). The lower IK,tail of female rabbit myocytes may contribute to the longer repolarization and the higher incidence of drug-associated torsade de pointes.
ABSTRACT
The effects of hepatic ischemia/reperfusion (I/R) injuries on hepatocellular viability and store-operated calcium current (Isoc) in isolated rat hepatocytes and the effects of 2-APB on storeoperated calcium current (Isoc) in isolated rat hepatocytes after hepaticischemia/reperfusion injuries were studied. Hepatic ischemia and reperfusion injury model was established and whole cell patch-clamp techniques were used to investigate the effects of 2-APB on Isoc. The results showed that ischemia/reperfusion injuries could significantly reduce hepatocellular viability and further increase Isoc in hepatocytes and 2-APB (20, 40, 60, 80, 100 μmol/L) produced a concentration-dependent decrease of Isoc with IC50 value of 64.63±10.56 μmol/L (n= 8). It was concluded that ischemia/reperfusion injuries could reduce hepatocellular viability, probably through increased Isoc in hepatocytes and 2-APB had a protective effect on ischemia/reperfusion-induced liver injury, probably though inhibiting Isoc.
ABSTRACT
To study the direct effect of somatostatin (SS) on calcium channel current (IBa) in guinea-pig gastric myocytes, IBa was recorded by using whole-cell patch clamp technique in single smooth muscle cells. Nicardipine (1microM), a L-type Ca2+ channel blocker, inhibited IBa by 98+/-1.9% (n=5), however IBa was decreased in a reversible manner by application of SS. The peak IBa at 0 mV were decreased to 95+/-1.1, 92+/-1.9, 82+/-4.0, 66+/-5.8, 10+/-2.9% at 10-10, 10-9, 10-8, 10-7, 10-5 M of SS, respectively (n=3~6; mean+/-SEM). The steady-state activation and inactivation curves of IBa as a function of membrane potentials were well fitted by a Boltzmann equation. Voltage of half-activation (V0.5) was -12+/-0.5 mV in control and -11+/-1.9 mV in SS treated groups (respectively, n=5). The same values of half-inactivation were -35+/-1.4 mV and -35+/-1.9 mV (respectively, n=5). There was no significant difference in activation and inactivation kinetics of IBa by SS. Inhibitory effect of SS on IBa was significantly reduced by either dialysis of intracellular solution with GDPbetaS, a non-hydrolysable G protein inhibitor, or pretreatment with pertussis toxin (PTX). SS also decreased contraction of guinea-pig gastric antral smooth muscle. In conclusion, SS decreases voltage-dependent L-type calcium channel current (VDCCL) via PTX- sensitive signaling pathways in guinea-pig antral circular myocytes.