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OBJECTIVE@#To investigate the effects and underlying mechanisms of Panax quinquefolium saponin (PQS) on energy deficiency in hypoxia-reperfusion (H/R) induced cardiomyocytes.@*METHODS@#The H/R injury involved hypoxia for 3 h and then reperfusion for 2 h. Cardiomyocytes recruited from neonatal rat ventricular myocytes (NRVMs) were randomly divided into control, H/R, H/R+compound C (C.C), H/R+PQS, and H/R+C. C+PQS groups. BrdU assay, lactase dehydrogenase (LDH) leakage and early apoptosis rate were evaluated to assess cell damages. Contents of high energy phosphate compounds were conducted to detect the energy production. Protein expression levels of adenosine monophosphate-activated protein kinase a (AMPKα), glucose transporter 4 (GLUT4), phosphate fructose kinase 2 (PFK2), fatty acid translocase/cluster of differentiation 36 (FAT/CD36), and acetyl CoA carboxylase 2 (ACC2) in the regulatory pathways were measured by Western blotting. Immunofluorescence staining of GLUT4 and FAT/CD36 was used to observe the mobilization of metabolic transporters.@*RESULTS@#PQS (50 mg/L) pretreatment significantly alleviated H/R-induced inhibition of NRVMs viability, up-regulation of LDH leakage, acceleration of early apoptosis, and reduction of energy production (P<0.05). Compared with the H/R group, up-regulated expression of AMPKα, GLUT4, PFK2, FAT/CD36 and ACC2 were observed, and more GLUT4 and FAT/CD36 expressions were detected on the membrane in the H/R+PQS group (P<0.05). These effects of PQS on H/R-induced NRVMs were eliminated in the H/R+C.C+PQS group (P<0.05).@*CONCLUSION@#PQS has prominent advantages in protecting NRVMs from H/R-induced cell damages and energy metabolic disorders, by activation of AMPKα-mediated GLUT4-PFK2 and FAT/CD36-ACC2 pathways.
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Aim To study the effects of daidzein on sodium channel current ( /Na) in ventricular myocytes of rats and the mechanism of its antiarrhythmia. Methods The effect of daidzein on the viability of ventricular myocytes was delected by MTT assay; single ventricular myocytes from rats were isolated by single enzymatic hydrolysis; the changes of /N, and its dynamic characteristics in rat ventricular myocytes before and after administration of daidzein were observed, recorded and analyzed by cell patch clamp technique. Results MTT experiments showed that the ICjo of daidzein was 30 to 100 jjimol • L"1 ,so the concentration of 0. 3 - 10 jimol • L"1 was chosen for the subsequent experiments. When daidzein was given 0. 3,1,3,10 pjnol • L"',the /Nb amplitude of ventricular myocytes in rats showed a concentration-dependent inhibition. The concentration of daidzein 0. 3 imol • L"1 also had certain effect on the time course of /Nt. The /Nl, peak decreased gradually over time. The 1,3,10 jimol • L"1 daidzein raised the I-U curve obviously. Under the same condition, the activation curve moved to the direction of depolarization. The steady-state inactivation curve shifted toward hyperpolarization, and the t value of the recovery curve was prolonged after inactivated state. Conclusions Daidzein significantly inhibited the Na∗ channel of ventricular myocardium in rats, which may l)e one of its mechanisms of anti-arrhythmia.
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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.
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To investigate the effects of isovitexin Ⅳ on transient outward potassium current in rat ventricular myocytes. In this study, MTT assay was used to investigate the safe range of isovitexin. The results showed that the IC₅₀ of the drug was in the range of 10-30 μmol•L⁻¹, and the drug concentration of 1-3 μmol•L⁻¹ for the patch clamp test was within the safe range. In addition, the single ventricular myocytes were obtained by single-enzymatic hydrolysis through aortic retrograde perfusion. The transient outward potassium current (Ito) of rat ventricular myocytes was guided and measured by whole-cell patch-clamp technique and the changes of current characteristics were recorded after isovite was applied. When the concentration of IV was less than 0.1 μmol•L⁻¹, there was no significant effect on Ito. However, with the increase in the concentration of IV (≥0.3 μmol•L⁻¹), the peak of Ito was decreased gradually, from (32.32±2.9) pA/pF to （25.83±4.3） pA/pF, 1 μmol•L⁻¹ IV and (19.51±3.5) pA/pF, 3 μmol•L⁻¹ IV respectively, with an inhibition effect in a concentration-dependent manner. In the range of 1-3 μmol•L⁻¹, IV down-regulated the I-V curve of Ito significantly. The activation curve showed that IV can enable the maximum half activation potential (V1/2) to move to the positive direction, and the V1/2 was increased from (19.59±1.6) mV to (22.81±1.7) mV and (28.86±1.4) mV at concentration of 1, 3 μmol•L⁻¹, meanwhile the activation curve moved to the right. However, the maximum half inactivating potential (V1/2) of the steady-state inactivation curve of Ito was significantly decreased from (－51.43±0.99) mV to (－61.81±1.3) mV with concentration of 1 μmol•L⁻¹ and (－71.50±1.4) mV with concentration of 3 μmol•L⁻¹. The inactivation time constant of recovery from inactivation (τ) was up-regulated significantly from (94.89±0.73) ms to (118.5±1.5) ms and (162.4±1.4) ms at concentration of 1, 3 μmol•L⁻¹ respectively. Meanwhile IV could enable the inactivation recovery curve to move to the right, which suggested that it can prolong the recovery time from inactivation of the transient outward potassium channel. In conclusion, isovitexin had a high inhibitory effect on Ito in rat ventricular myocytes.
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Objective To observe the influence of Kuailvning capsule(KLN)and its drug serum on the concentration of Ca2 + in rat ventricular muscle cells.Methods SD rats were randomly divided into five groups:the control group,serum control group,KLN high -dose group,KLN medium -dose group and KLN low -dose group,six mice in each group.The rat ventricular myocytes were separated by enzymatic hydrolysis.The influence of KLN and its drug serum on the concentration of Ca2 + in rat ventricular muscle cells were observed by Fluo -3 /AMprobe.Results The mean fluorescence intensity of cytosolic Ca2 + in the KLN high -dose group,KLN medium -dose group and KLN low -dose group after 50s,100s,150s,200s,250s were [(18.75 ±1.55),(16.69 ±0.93),(17.76 ±1.26)], [(25.47 ±1.118),(17.86 ±1.49),(17.81 ±1.13)],[(29.05 ±1.31),(20.14 ±1.73),(18.26 ±1.37)], [(35.21 ±1.33),(23.19 ±0.97),(18.18 ±1.46)],[(41.08 ±1.21),(26.34 ±1.69),(17.91 ±1.01)], which were higher than those in the control group(F =5.556,7.007,8.816,10.208,12.232,all P 0.05).Conclusion KLN drug serum can promote myocardial cell spon-taneous extracellular calcium influx,the mechanism of KLN antiarrhythmic effect may be related to the Ca2 + channel.
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Objective To observe the effects of neuregulin‐1 (NRG‐1)on calcium transients in mouse ventricular myo‐cytes.Methods Nine C57BL/6 mice of male were randomly dived into 3 groups :the blank control group ,NRG‐1 group ,and iso‐proterenol(ISO)group.Their hearts were removed and immediately cannulated via the aorta and retrogradely perfused with en‐zymatic isolation solution to get single ventricular cell by Langendorff system.Myocytes were loaded with the Ca2+ indicator Fluo‐4 and subjected to electrical field stimulation at 0.5 or 1 Hz by using living cells workstation.The change of fluorescene in‐tensity was recorded simultaneously in each group.Results Compared with the blank control group ,NRG‐1 group had signifi‐cantly increased Ca2+ transient amplitude ΔF/F0 (n=10 ,P0.05).Conclusion NRG‐1 can increase Ca2+ transient amplitude and Ca2+ transients and reduce the time interval of Ca2+ transients.
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Aim To investigate the antiarrhythmic mechanism of taurine-magnesium coordination com-pound on abnormal sodium current channel ( INa ) in-duced by hypoxia-reoxygenation in ventricular myocytes of rats. Methods Single ventricular myocytes were i-solated from each rat heart using enzymatic dissociation through Langendorff retrograde aortic perfusion. Whole-cell patch clamp was applied in voltage clamp mode to record INa both in normal ventricular myocytes and single ventricular myocytes of arrhythmia induced by hypoxia-reoxygenation. Results The peak density of INa was changed from ( 56. 89 ± 2. 07 ) pA/pF to (35. 05 ± 1. 52) pA/pF( n=6, P 0. 05), in a concentration-dependent manner, while amioda-rone restored it to (39. 44 ± 1. 24) pA/pF (n=6,P<0. 01 ) . Both high concentration of TMCC and amioda-rone could shift the I-V curve downward. In addition, TMCC and amiodarone could restore the INa inactivation curve and slow down its inactivation, whereas the acti-vation curves showed no significant differences among groups. Conclusion TMCC(200,400 μmol·L-1) could restore the H/R induced INa reduction and shift the I-V curve downward by inhibiting steady-state inac-tivation, which is suggested to be one of the mecha-nisms of the antiarrhythmic effects of TMCC in hypoxia-reoxygenation model.
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Objective: To investigate the effects of serum containing dioscin on sodium current (INa) and reveal the mechanisms of cardioprotection and antiarrhymias. Methods: Serum was obtained from the aortaventralis from Wistar rats after ig administration 4 d of dioscin 300 mg/kg, twice daily for 4 d. Single ventricular myocytes were isolated from adult rat hearts by enzymatic dissociation and the effects of dioscin on INa were observed by whole-cell patch clamp. Results: Serum containing dioscin shifted downward the I-V curve with increased peak current density. With the effects of 1, 10, and 100 μL serum containing dioscin, the peak current density was dose-dependently changed from (-52.10 ± 3.80) pA/pF to (-76.44 ± 4.09) pA/pF and (-81.96 ± 4.70) pA/pF, respectively (P < 0.01 vs control); Dioscin facilitated the activation process with the inactivation process unchanged. The half activation potential was changed from (-57.69 ± 1.86) mV to (-59.71 ± 2.57) mV, ( -66.56 ± 1.32) mV (P < 0.01 vs control), and (-68.52 ± 3.91) mV (P < 0.01 vs control), respectively; The recovery process of sodium channel was accelerated by 1, 10, and 100 μL serum containing dioscin with the recovery constant τ changed from (150.73 ± 21.49) ms to (143.19 ± 13.88) ms, (84.83 ± 18.03) ms (P < 0.01 vs control), and (80.63 ± 13.89) ms (P < 0.01 vs control). Conclusion: Serum containing dioscin could increase the sodium current by facilitating the activation process and accelerating the recovery process of sodium channel.
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Cardiovascular complications are a leading cause of mortality in patients with diabetes mellitus (DM). The present study was designed to investigate the effects of trimetazidine (TMZ), an anti-angina drug, on transient outward potassium current (Ito) remodeling in ventricular myocytes and the plasma contents of free fatty acid (FFA) and glucose in DM. Sprague-Dawley rats, 8 weeks old and weighing 200-250 g, were randomly divided into three groups of 20 animals each. The control group was injected with vehicle (1 mM citrate buffer), the DM group was injected with 65 mg/kg streptozotocin (STZ) for induction of type 1 DM, and the DM + TMZ group was injected with the same dose of STZ followed by a 4-week treatment with TMZ (60 mg·kg-1·day-1). All animals were then euthanized and their hearts excised and subjected to electrophysiological measurements or gene expression analyses. TMZ exposure significantly reversed the increased plasma FFA level in diabetic rats, but failed to change the plasma glucose level. The amplitude of Ito was significantly decreased in left ventricular myocytes from diabetic rats relative to control animals (6.25 ± 1.45 vs 20.72 ± 2.93 pA/pF at +40 mV). The DM-associated Ito reduction was attenuated by TMZ. Moreover, TMZ treatment reversed the increased expression of the channel-forming alpha subunit Kv1.4 and the decreased expression of Kv4.2 and Kv4.3 in diabetic rat hearts. These data demonstrate that TMZ can normalize, or partially normalize, the increased plasma FFA content, the reduced Ito of ventricular myocytes, and the altered expression Kv1.4, Kv4.2, and Kv4.3 in type 1 DM.
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Animals , Rats , Diabetes Mellitus, Experimental/metabolism , Diabetes Mellitus, Type 1/metabolism , Myocytes, Cardiac/drug effects , Potassium Channels/drug effects , Trimetazidine/pharmacology , Vasodilator Agents/pharmacology , Fatty Acids/blood , Glucose/analysis , Myocytes, Cardiac/metabolism , Potassium Channels/metabolism , Rats, Sprague-Dawley , StreptozocinABSTRACT
We carried out a series of experiment demonstrating the role of mitochondria in the cytosolic and mitochondrial Ca2+ transients and compared the results with those from computer simulation. In rat ventricular myocytes, increasing the rate of stimulation (1~3 Hz) made both the diastolic and systolic [Ca2+] bigger in mitochondria as well as in cytosol. As L-type Ca2+ channel has key influence on the amplitude of Ca2+-induced Ca2+ release, the relation between stimulus frequency and the amplitude of Ca2+ transients was examined under the low density (1/10 of control) of L-type Ca2+ channel in model simulation, where the relation was reversed. In experiment, block of Ca2+ uniporter on mitochondrial inner membrane significantly reduced the amplitude of mitochondrial Ca2+ transients, while it failed to affect the cytosolic Ca2+ transients. In computer simulation, the amplitude of cytosolic Ca2+ transients was not affected by removal of Ca2+ uniporter. The application of carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) known as a protonophore on mitochondrial membrane to rat ventricular myocytes gradually increased the diastolic [Ca2+] in cytosol and eventually abolished the Ca2+ transients, which was similarly reproduced in computer simulation. The model study suggests that the relative contribution of L-type Ca2+ channel to total transsarcolemmal Ca2+ flux could determine whether the cytosolic Ca2+ transients become bigger or smaller with higher stimulus frequency. The present study also suggests that cytosolic Ca2+ affects mitochondrial Ca2+ in a beat-to-beat manner, however, removal of Ca2+ influx mechanism into mitochondria does not affect the amplitude of cytosolic Ca2+ transients.
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Animals , Rats , Computer Simulation , Cytosol , Hydrazones , Ion Transport , Membranes , Mitochondria , Mitochondrial Membranes , Muscle Cells , NitrilesABSTRACT
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.
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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.
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Objective To investigate the effects of docosahexaenoic acid (DHA) on action potential (AP)and transient outward potassium channel (Ito) in rat ventricular myocytes in order to evaluate the anti-arrhythmia mechanism of DHA. Method The rat ventricular myocytes were isolated by using enzyme digestion method. AP and Ito of individual ventricular myocyte were recorded by using patch-clamp technique in whole-cell configuration at room temperature. The effects of DHA on AP and Ito were observed when it was applied in 0 μmol/L, 20 μmol/L, 40 μmol/L, 60 μmol/L, 80 μmol/L, 100 μmol/L and 120μmol/L separaterly. Results The 25%,50% and 90% of action potential duration (APD25, APD50 and APD90) were gradually prolonged with the escalation of concentration of DHA ( P ＜ 0.05, n= 20). The effects of DHA of different concentrations on AP maximal velocity (Vmax), AP amplitude (APA) and AP overshoot (OS) did not produce significantly different results (P ＞ 0.05, n= 20). The degree of blockade of Ito was concentration-dependent as different concentrations of DHA were applied, and as the concentration of DHA was escalated, the I-V curves went downwards, the stably inactivated curves shifted to the lift, and the time taken for recovery from inactivation prolonged ( P ＜ 0.05, n =20). However, the different concentrations of DHA did not produce different effects on stably activated curves ( P＞ 0.05). The Itos were blocked to (2.61 ± 0.26)%, (21.79±4.85)%, (63.11 ± 6.57)%, 75.52±7.26 ) %, (81.82 ± 7.63) % and (84.33 ± 8.25) % by the above given concentrations of DHA respectively under given potential equaling to + 70 mV( P ＜ 0.05, n = 20), and the half-effect concentration (EC50) of DHA on Ito was(49.11±2.68) umol/L. Conclusions The effects of DHA on APD and Ito may be one of the anti-arrhythmia mechanism of DHA.
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Objective: To study the effect of low concentration of ouabain MUM on intracellular calcium concentration ([Ca2+]i) in guinea pig ventricular myocytes and to understand whether low concentration of OUA can increase [Ca2+]i through Na+, K+-ATPase channel. Methods: The guinea pig ventricular myocytes were obtained by enzymatic digestion and the [Ca2+]i fluorescent density of individual myocytes was observed under confocal laser scanning microscope. The isolated ventricular myocytes were then incubated with different concentrations of ouabain(10-9, 10-8, 10-7, 10-6 mol · L-1). The sediment was subjected to Western blot analysis to assess the phosphorylation of Src by OUA. Results: In normal Tyrode' s solution and Ca2+-free Tyrode's solution, OUA (1 × 10-9 -1 × 10-6) mol · L-1 elevated [Ca2+]i in a concentration-dependent manner, with the elevation in normal Tyrode's solution more obvious (P < 0.05). Genistein (GST) (1, 10, 50, and 100 μmol - L-1) abolished the OUA-induced increases of [Ca2+]i in a concentration-dependent manner. There were two tyrosine-phosphorylated bands, with the molecular weights being 120 000 and 70 000. Compared with control group, the densities of the 2 bands in all OUA groups were significantly higher (P<0.05) and GST could obviously inhibit the elevating effect of OUA. Conclusion: Low concentration of OUA may promote opening of Ca2+ channel and release of intracellular Ca2+, and subsequently elevate intracellular free calcuim through phosphorylation of tyrosine and activition of OUA/Na+, k+-ATPase/Src signal transduction pathway.
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Objective To study the influence of arachidonic acid (AA) on L-type calcium channel in rabbits sin-gle cardiomyocyte and its mechanism of antiarrhythmia. Method The single ventricular cardiomyocyte was isolat-ed by using enzyme dispersion method and whole-cell clamp-patch technique was used to record L-type calcium current.All data were analyzed using ANOVA. Results AA inhibited Ica-L in a concentration-dependent manner. The application of 3 μmol/L, 10 μmol/L and 20 μmol/L arachidonic acid reduced the density of peak Ica-L from (10.79±0.93)pA/pF to (8.99±0.43)pA/pF to (7.60±0.35)pA/pF and to (5.60±0.30)pA/pF, respctive-ly (n=7, P<0. O1 ). The Ica-Lpartially resumed after washout. The AA up-shifted the I-V curves of Ica-L without changes of their shape,peak and reverse potentials. The AA also markedly shifted the inactivation curve to left, and prolonged the recorvery time from inactivation,but did not change the curve of calcium channel activation. Con-clustions By acceleration of L-type calcium channel inactivation and prolongation of recorvery time from inactiva-fion,arachidonic acid can reduce the calcium ion influe and prolong effective refractory period, playing the role of antiarrhythmia.
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To investigate the effect of sea anemone toxin anthopleurin-Q (AP-Q) on potassium currents in isolated rats and guinea pig ventricular myocytes.Methods The ventricular cells of guinea pigs and SD rats were obtained by enzymatic dissociation method.Whole cell patch clamp technique was used to record potassium currents (Ito,IK,and IK1).Results AP-Q 3-100 nmol/L increased Ito in a concentration-dependent manner,with an EC50 value of 12.7 nmol/L.At a potential of +50mV,AP-Q 10nmol/L increased Ito from (13.3±3.4) pA pF-1 to (19.46±4.3) pA pF-1.AP-Q 0.1-100 nmol/L increased IK and IK tail in a concentration-dependent manner with EC50 values of 4.7 nmol/L and 5.0 nmol/L,respectively.AP-Q 1 pmol/L-100 nmol/L increased IK1 in dose-dependent manner,with an EC50 of 0.2 nmol/L.Conclusions The effect of AP-Q on Ito,IK and IK1 may partly explain its mechanism in shortening APD and increasing RP.(J Geriatr Cardiol 2008;5:243-247)
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Objective To investigate the alterations and molecular mechanism of transient outward potassi- um currents(I_(to)) in ventricular myocytes from diabetic rats and explore the mechanism of predisposition of arrhyth- mias in diabetes.Methods The diabetes model was established by a single injection of streptozocin(STZ,65 mg/ kg,pH=4.5) I.P.in male Sprague-Dawley rats with weight 150-200 g.Ventricular myocytes were isolated by enzymatic perfusion.The currents were recorded with the whole-cell patch clamp technique,and gene expres- sions of channel-forming subunits (Kv4.2,Kv4.3 and Kv1.4) were semi-quantified by the technique of reverse transcriptase-polymerase chain reaction(RT-PCR).Results The I_(to) density (+70 mV) decreased significantly in diabetic rats compared with controls[control:(30.6?3.8)pA/pF(n=9) vs diabetes:(18.9?3.3)pA/pF(n= 29)(P
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Objective To investigate the effect and mechanism of sphingosine 1-phosphate(S1P)on action potential(AP)and voltage-dependent potassium current(KV)in isolated guinea pig ventricular myocytes.Methods The ventricular myocytes were isolated by using Langendorff perfusion method.The AP and KV were recorded by whole cell patch-clamp recording technique.Results S1P prolonged the 50% and 90% action potential duration(APD50 and APD90)and decreased KV which were blocked by pertussis toxin(PTX)or Calphostin C.Conclusion S1P decreased KV in a PKC pathway and prolonged action potential duration in guinea-pig ventricular myocytes.
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BACKGROUND: Whereas sevoflurane (SEVO) has been reported to prolong the QT interval, little has been known on the electrophysiologic effects of SEVO which contributes to the prolongation of action potential (AP) duration. METHODS: The ventricular myocytes were obtained from enzymatically treated rat hearts. The standard whole cell voltage-clamp methods were used. The AP was measured using current clamp technique. As a repolarizing K+ current, the transient outward K+ current (I(to)), the sustained outward K+ current (I(sus)), and the inwardly rectifying K+ current (I(kI)) were measured. The L-type Ca2+ current (I(Ca), L) was also obtained. After the baseline measurements, the myocytes were exposed to 1.7 and 3.4% SEVO. SEVO concentrations in Tyrode superfusate at room temperature were 0.35 and 0.7 mM for 1.7 and 3.4% SEVO, respectively. Results are mean +/- SEM. RESULTS: SEVO prolonged the AP duration, while the amplitude and the resting membrane potential remained unchanged. At membrane potential of +60 mV, peak I(to) was significantly reduced by 18 +/- 2 and 24 +/- 2% by 0.35 and 0.7 mM SEVO, respectively. 0.7 mM SEVO did not shift the steady-state inactivation curve. Isus was unaffected by 0.7 mM SEVO. The I(kI) at -130 mV was little altered by 0.7 mM SEVO. I(Ca), L was significantly reduced by 28 +/- 3 and 33 +/- 1% by 0.35 and 0.7 mM SEVO, respectively. CONCLUSIONS: Prolongation of AP duration by SEVO in rat ventricular myocytes is likely to be caused by a reduction of I(to). Resting membrane potential was unaffected by SEVO, which seems to be related to no alteration of I(kI).
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Animals , Rats , Action Potentials , Heart , Membrane Potentials , Muscle CellsABSTRACT
BACKGROUND: Desflurane has been reported to prolong the QTc. Several ionic currents that contribute to the prolongation of the action potential (AP) duration were investigated using guinea pig (GP) and rat ventricular myocytes. METHODS: The normal APs were measured in isolated GP papillary muscles at 37 degrees C. Ventricular myocytes were obtained from GP and rat hearts. Both the delayed outward K+ current (I(K)) and the inward rectifier K+ current (I(KI)) were assessed using a voltage ramp protocol. A more detailed study on the I(K) was performed. The ICa, L was measured. In the rat ventricular myocytes, the transient outward K+ current (I(to)) was obtained. All the patch clamp experiments were carried out at room temperature. The values are presented as mean +/- SD. RESULTS: 0.91 mM desflurane significantly prolonged the APD in the GP ventricular myocytes. Using a linear voltage ramp protocol, the I(KI) at -130 mV and the peak outward I(KI) at -60 to -50 mV were not found to be significantly reduced by 0.78 and 1.23 mM desflurane, respectively. However, the peak outward I(K) at +60 mV was significantly reduced to 63 +/- 19% and 58 +/- 12% of the baseline by 0.78 and 1.23 mM desflurane, respectively. At a membrane potential of +60 mV, 0.78 and 1.23 mM desflurane reduced the Ito to 80 +/- 8% and 68 +/- 7%, respectively. A concentration-dependent reduction in the ICa, L was observed. CONCLUSIONS: The prolongation of the APD induced by clinically relevant concentrations of desflurane in GP and rat ventricular myocytes is most likely the result of I(K) and I(to) suppression.