Effects of hydrogen peroxide on voltage-dependent K+ currents in human cardiac fibroblasts through protein kinase pathways

Human cardiac fibroblasts (HCFs) have various voltage-dependent K+ channels (VDKCs) that can induce apoptosis. Hydrogen peroxide (H2O2) modulates VDKCs and induces oxidative stress, which is the main contributor to cardiac injury and cardiac remodeling. We investigated whether H2O2 could modulate VDKCs in HCFs and induce cell injury through this process. In whole-cell mode patch-clamp recordings, application of H2O2 stimulated Ca2+-activated K+ (K(Ca)) currents but not delayed rectifier K+ or transient outward K+ currents, all of which are VDKCs. H2O2-stimulated K(Ca) currents were blocked by iberiotoxin (IbTX, a large conductance K(Ca) blocker). The H2O2-stimulating effect on large-conductance K(Ca) (BK(Ca)) currents was also blocked by KT5823 (a protein kinase G inhibitor) and 1 H-[1, 2, 4] oxadiazolo-[4, 3-a] quinoxalin-1-one (ODQ, a soluble guanylate cyclase inhibitor). In addition, 8-bromo-cyclic guanosine 3', 5'-monophosphate (8-Br-cGMP) stimulated BK(Ca) currents. In contrast, KT5720 and H-89 (protein kinase A inhibitors) did not block the H2O2-stimulating effect on BK(Ca) currents. Using RT-PCR and western blot analysis, three subtypes of K(Ca) channels were detected in HCFs: BK(Ca) channels, small-conductance K(Ca) (SK(Ca)) channels, and intermediate-conductance K(Ca) (IK(Ca)) channels. In the annexin V/propidium iodide assay, apoptotic changes in HCFs increased in response to H2O2, but IbTX decreased H2O2-induced apoptosis. These data suggest that among the VDKCs of HCFs, H2O2 only enhances BK(Ca) currents through the protein kinase G pathway but not the protein kinase A pathway, and is involved in cell injury through BK(Ca) channels.

Effects of retinal ganglion cell apoptosis on delayed rectifier K+currents / 中国病理生理杂志

AIM: To investigate the effects of rat retinal ganglion cell (RGC) apoptosis on delayed rectifier K+currents (IK).METHODS:The retinas of 2~3 d newborn Sprague-Dawley rats were dissociated into cell suspension by trypsin digestion .The RGCs were cultured and divided into control group , pressure 0.5 h group, pressure 1 h group, pressure 1.5 h group and pressure 2 h group.The cells were cultured regularly for 6 d in control group , and the cells in other groups were cultured regularly for 6 d and gave pressure of 80 mmHg for 0.5 h, 1 h, 1.5 h and 2 h, respectively. The rhodamine 123 fluorescence from labeled RGC mitochondrion was detected by continuous wavelength multifunctional microplate detection instrument.The membrane capacitance (Cm) in different groups and IK in the pressure 1 h group were recorded from the RGCs by whole-cell patch-clamp technique .RESULTS:No difference of rhodamine 123 fluorescence in the RGC mitochondria between control group and pressure 0.5 h group was observed .Rhodamine 123 fluorescence in the other 3 groups was significantly lower than that in control group (P<0.05).No difference of the Cm between control group and pressure 0.5 h group was found, and the Cm in the other 3 groups was significantly lower than that in control group (P<0.05).The amplitudes of IK were higher than that in control group .At the test potential from -10 mV to 60 mV, the current density in pressure 1 h group was significantly higher than that in control group (P<0.05).The maximal conduc-tion ( Gmax ) in pressure 1 h group was significantly higher than that in control group .The voltage for IK channel half-activa-tion ( V1/2 ) in pressure 1 h group declined comparison with control group ( P<0.01 ) , and the k value had no significant difference between the 2 groups.CONCLUSION:Retinal ganglion cell apoptosis accompanies with delayed rectifier K +current enhancement .

Effects of tumor necrosis factor-α on MAPD between endocardium and epicardium in isolated heart tissues and study for mechanism / 中国免疫学杂志

Objective: To explore the relationship between expression of tumor necrosis factor-α( TNF-α) and electrophysiological heterogeneity in isolated heart tissues and isolated rat ventricular myocytes.The arrhythmogenic mechanisms of TNF-αwere further studied.Methods:Langendorff perfused heart tissues models were used to verify the arrhythmogenic effects of TNF-α.The monophasic action potentials( MAPs) of the endocardium and epicardium from the isolated heart tissues were recorded by elec-trophysiological experiments.The isolated rat ventricular myocytes were obtained by enzymatic dissociation.K+currents(Ito,IK1)were recorded by using whole cell patch clamp technique.Results: Compared to the control group, the difference in MAPD between endocardium and epicardium dramatically increased with TNF-α( P<0.05 ) .TNF-αcould cause MAP duration ( MAPD ) prolongation, and a single dose of TNF-αdifferentially affected the MAPs of endocardium and epicardium of isolated heart tissues.Compared to the control group,the K+currents(Ito,IK1)were dose-dependently decreased with TNF-αin rat ventricular myocytes(P<0.05).However, etanercept had no effects on the MAPD in the absence of TNF-α.Conclusion:TNF-α-induced heterogeneity of MAPD between the endo-cardium and epicardium may provide the substrate for the onset of ventricular arrhythmias during acute myocardial infarction.The effect might be associated with TNF-αcontribute to re-entrant ventricular arrhythmias which resulted from decreased K+currents(Ito,IK1).

Four Voltage-Gated Potassium Currents in Trigeminal Root Ganglion Neurons

Various voltage-gated K+ currents were recently described in dorsal root ganglion (DRG) neurons. However, the characterization and diversity of voltage-gated K+ currents have not been well studied in trigeminal root ganglion (TRG) neurons, which are similar to the DRG neurons in terms of physiological roles and anatomy. This study was aimed to investigate the characteristics and diversity of voltage-gated K+ currents in acutely isolated TRG neurons of rat using whole cell patch clamp techniques. The first type (type I) had a rapid, transient outward current (I(A)) with the largest current size having a slow inactivation rate and a sustained delayed rectifier outward current (I(K)) that was small in size having a fast inactivation rate. The I(A) currents of this type were mostly blocked by TEA and 4-AP, K channel blockers whereas the I(K) current was inhibited by TEA but not by 4-AP. The second type had a large I(A) current with a slow inactivation rate and a medium size-sustained delayed IK current with a slow inactivation rate. In this second type (type II), the sensitivities of the I(A) or I(K) current by TEA and 4-AP were similar to those of the type I. The third type (type III) had a medium sized I(A) current with a fast inactivation rate and a large sustained I(K) current with the slow inactivation rate. In type III current, TEA decreased both I(A) and I(K) but 4-AP only blocked I(A) current. The fourth type (type IV) had a smallest I(A) with a fast inactivation rate and a large IK current with a slow inactivation rate. TEA or 4-AP similarly decreased the I(A) but the I(K) was only blocked by 4-AP. These findings suggest that at least four different voltage-gated K+ currents in biophysical and pharmacological properties exist in the TRG neurons of rats.

Effects of Atractylodes Macrocephala on the Cytomembrane Ca2+-activated K+ Currents in Cells of Human Pregnant Myometrial Smooth Muscles / 华中科技大学学报（医学）（英德文版）

The study examined the inhibitory effect of Atractylodes macrocephala (AM) on the uterine contraction during premature delivery and explored its electrophysiological mechanism by studying the effects of AM on the Ca2+-activated K+ currents of pregnant human myometrial smooth muscle cells with or without the treatment with interleukin-6. Single cells were acutely isolated from pregnant human myometrial smooth muscles. Whole-cell Ca2+-activated K+ currents were recorded by using an Axopatchl-D amplifier. The cells were divided into three groups: group A in which AM was added into perfusate, group B, in which intefleukin-6 was added into perfusate) and group C in which AM was added into perfusate after addition of interleukin-6. IL-6 10 ng/mL inhibited Bkca by 36.9%±13.7% as compared with control (P<0.01). AM at 2 mg/mL raised Bkca by 36.7%±22.6% or 45.2%±13.7% with or without the treatment of IL-6, respectively (P<0.01). It is concluded that AM was able to enhance the Bkca of pregnant human myometrial smooth muscle cells treated or un- treated with interleukin-6 and its effect on the Bkca IL-treated cells was stronger that its effect on Bkca of untreated cells. Our results suggested that AM can help to maintain the membrane potentials and the resting status of pregnant human myometrial smooth muscle cells.

Heterogeneous Composition of Voltage-Dependent K+ Currents in Hepatic Stellate Cells

PURPOSE: Hepatic stellate cells (HSC) are a type of pericyte with varying characteristics according to their location. However, the electrophysiological properties of HSC are not completely understood. Therefore, this study investigated the difference in the voltage-dependent K(+) currents in HSC. MATERIALS AND METHODS: The voltage-dependent K(+) currents in rat HSC were evaluated using the whole cell configuration of the patch-clamp technique. RESULTS: Four different types of voltage-dependent K(+) currents in HSC were identified based on the outward and inward K(+) currents. Type D had the dominant delayed rectifier K(+) current, and type A had the dominant transient outward K(+) current. Type I had an inwardly rectifying K(+) current, whereas the non-type I did not. TEA (5mM) and 4-AP (2mM) suppressed the outward K(+) currents differentially in type D and A. Changing the holding potential from -80 to -40mV reduced the amplitude of the transient outward K(+) currents in type A. The inwardly rectifying K(+) currents either declined markedly or were sustained in type I during the hyperpolarizing step pulses from -120 to -150mV. CONCLUSION: There are four different configurations of voltage-dependent K(+) currents expressed in cultured HSC. These results are expected to provide information that will help determine the properties of the K(+) currents in HSC as well as the different type HSC populations.

The Effect of Midazolam on Outward K+ Channel Currents in Rabbit Cerebral Arterial Smooth Muscle Cells / 대한마취과학회지

BACKGROUND: Midazolam has a direct relaxing effect on vascular smooth muscle, but the mechanisms that this agent produces muscle relaxation are not fully understood. The current study was performed to identify the effects of the midazolam on K+ channels current in rabbit cerebral arterial smooth muscle cells. METHODS: Whole cell patch-clamp recording technique was used to evaluate the effects of midazolam (0.1 to 100micrometer) on outward K+ channel currents in dispersed rabbit cerebral arterial smooth muscle cells. RESULTS: Outward K+ currents of rabbit cerebral artery smooth muscle cells were voltage-dependent. Midazolam (10, 100micrometer) tested significantly inhibited outward K+ currents in a dose-dependent manner and half-blocking concentration (IC50) was 15.94micrometer at 60 mV. CONCLUSIONS: Midazolam inhibit outward K+ currents of rabbit cerebral arterial smooth muscle cells. Further study will be needed to determine the effect of midazolam on calcium channel current because it is unclear if the inhibitory effect of midazolam on outward K+current induces vasoconstriction.

Effects of Tamoxifen on the Voltage-dependent Ionic Currents in Mouse Colonic Smooth Muscle Cells / 대한소화기학회지

BACKGROUND/AIMS: Tamoxifen is a widely used anticancer drug for breast cancer with frequent gastrointestinal side effects. Changes in gastrointestinal motility is associated with altered activities of membrane ion channels. Ion channels have important role in regulating membrane potential and cell excitability. This study was performed to investigate the effects of tamoxifen on the membrane ionic currents in colonic smooth muscle cells. METHODS: Murine colonic smooth muscle cells were isolated from the proximal colon using collagenase, and the membrane currents were recorded using a whole-cell patch clamp technique. RESULTS: Two types of voltage-dependent K+ currents were recorded (A-type and delayed rectifier K+ currents). Tamoxifen inhibited both types of voltage-dependent K+ currents in a dose-dependent manner. However, tamoxifen did not change the half-inactivation potential and the recovery time of voltage-dependent K+ currents. Chelerythrine, a protein kinase C inhibitor or phorbol 12, 13-dibutyrate, a protein kinase C activator did not affect the voltage-dependent K+ currents. Guanosine 5'-O-(2-thio-diphosphate) did not affect the tamoxifen-induced inhibition of voltage-dependent K+ currents. Tamoxifen inhibited voltage-dependent Ca2+ currents completely in whole-test ranges. CONCLUSIONS: These results suggest that tamoxifen can alter various membrane ionic currents in smooth muscle cells and cause some adverse effects on the gastrointestinal motility.

The Effect of Propofol on Outward K+ Currents in Canine Colonic Myocytes / 대한마취과학회지

BACKGROUND: Propofol (2,6-diisopropylphenol) is a widely used intravenous anesthetic, and the effects of propofol on several ion channels have been studied at the whole cell and single-channel levels. However, in general there is no report on the effect of propofol on outward K+ currents in canine colonic myocytes, in which there are two types of outward K+ currents, a large-conductance Ca2+-activated K+ current and a classical delayed rectifier K+ current. We examined the effects of propofol on the two types of outward K+ currents the kinetics involved. METHODS: Experiments were performed on freshly dispersed smooth muscle cells from the circular muscle layer of the proximal canine colon. Outward currents were recorded using the patch clamp technique in the whole cell configuration. RESULTS: The application of propofol (600 nM-600microM) decreased net outward current in a dose-dependent manner. Propofol (6-60microM) also decreased peak delayed rectifier K+ currents. Pretreatment with TEA abolished propofol effects on delayed rectifier K+ currents. However, propofol still decreased delayed rectifier K+ currents in the presence of 4-AP. CONCLUSIONS: These data suggest that propofol decrease net outward K+ currents primarily by inhibiting large-conductance Ca2+-activated K+ currents and 4-AP resistant delayed rectifier K+ currents. These results suggest that propofol action on outward currents may depend on the different blocking mechanisms of the different types of K+ channels. If propofol cannot induce contraction, Ca2+ currents in colonic myocytes warrant further study.

Characteristics of Potassium and Calcium Currents of Hepatic Stellate Cells (Ito) in Rat

Hepatic stellate cells (HSCs) are known to play a role in the pathogenesis of the increased intrahepatic vascular resistance found in chronic liver diseases. The aim of this study was to evaluate the K+ and Ca2+ currents in cultured HSCs from rat liver, through the patch-clamp technique. Most cells were positive for desmin immunostain after isolation and in alpha-smooth muscle actin immunostain after 10 - 14 days of culturing. Outward and inward rectifying K+ currents were confirmed. Two different types of K+ currents were distinguished: one with the inward rectifying current and the other without. The outward K+ currents consisted of at least four components: tetraethylammonium (TEA) -sensitive current, 4-aminopyridine (4-AP) -sensitive current, pimozide-sensitive current and three blocker-resistant current. The peaks of the outward K+ currents evoked by a depolarizing pulse were decreased to 32.0 +/- 3.0, 62.8 +/- 3.7 and 32.8 +/- 3.5% by 5 mM TEA, 2 mM 4-AP and 15microM pimozide, respectively. Moreover, the combined application of three blockers caused 86.6 +/- 4.8% suppression. The inward currents evoked hyperpolarizing pulses were inwardly rectifying and almost blocked by Ba2+. Elevation of external K+ increased the inward current amplitude and positively shifted its reversal potential. Voltage- dependent Ca2+ currents which were completely abolished by Cd2+ and nimodipine were detected in 14 day cultured HSCs. In this study, the cultured HSCs were found to express outward K+ currents composed of multiple pharmacological components, Ba2+-sensitive inward rectifying K+ current and L-type Ca2+ current.

Ca2 -activated K Currents of Pancreatic Duct Cells in Guinea-pig

There are numerous studies on transepithelial transports in duct cells including Cl and/or HCO3. However, studies on transepithelial K transport of normal duct cells in exocrine glands are scarce. In the present study, we examined the characteristics of K currents in single duct cells isolated from guinea pig pancreas, using a whole-cell patch clamp technique. Both Cl and K conductance were found with KCl rich pipette solutions. When the bath solution was changed to low Cl, reversal potentials shifted to the negative side, 75 4 mV, suggesting that this current is dominantly selective to K. We then characterized this outward rectifying K current and examined its Ca2 dependency. The K currents were activated by intracellular Ca2. 100 nM or 500 nM Ca2 in pipette significantly (P< 0.05) increased outward currents (currents were normalized, 76.8 7.9 pA, n=4 or 107.9 35.5 pA, n=6) at 100 mV membrane potential, compared to those with 0 nM Ca2 in pipette (27.8 3.7 pA, n=6). We next examined whether this K current, recorded with 100 nM Ca2 in pipette, was inhibited by various inhibitors, including Ba2, TEA and iberiotoxin. The currents were inhibited by 40.4 % (n=3), 87.0 % (n=5) and 82.5 % (n=9) by 1 mM Ba2, 5 mM TEA and 100 nM iberiotoxin, respectively. Particularly, an almost complete inhibition of the current by 100 nM iberiotoxin further confirmed that this current was activated by intracellular Ca2. The K current may play a role in secretory process, since recycling of K is critical for the initiation and sustaining of Cl or HCO3 secretion in these cells.

Congenital LQT Syndromes: From Gene to Torsade de Pointes

Congenital Long QT syndrome (LQTs) is a relatively rare pathologic disorder but results frequently in sudden cardiac death. Of the six LQTs that have been clinically described, five have been worked out for their genetic and biophysical profile. Most are generated by mutations which cause a loss of function in two delayed K+currents, iKs and iKr. One syndrome is generated by mutations in the Na channel which causes essentially a gain of function in the channel. Clinically the syndromes are characterized by slowed repolarization of the cardiac ventricular action potential and the occurrence of typical arrhythmias with undulating peaks in the electrocardiogram, called Torsade de Pointes. Arrhythmias are initiated by early or delayed afterdepolarizations and continue as reentry. Triggers for cardiac events are exercise (swimming; LQT1), emotion (arousal; LQT2) and rest/sleep (LQT3). beta-blockers have a high efficacy in the treatment of LQT1 and LQT2. In LQT3 their use is questionable. The study of congenital LQTsyndromes is a remarkable example of how basic and clinical science converge and take profit of each other's contribution.

Stationary outward and transient Ca2+-dependent currents in hamster oocytes

The outward currents elicited in hamster eggs by depolarizing pulses were studied. The currents appeared to comprise at least two components, a transient outward component (Ito) and a steady-state outward component (Iinfin). Ito was transiently followed by the cessation of inward Ca2+ current (ICa), and its current-voltage (I-V) relation was a mirror image of that of ICa. Either blockade of ICa by Co2+ or replacement of Ca2+ with Sr2+ abolished Ito without change in Iinfin. Intracellular EGTA (10 mM) inhibited Ito but not Iinfin. suggesting strongly that generation of Ito requires intracellular Ca2+. Apamin (1 nM) abolished selectively Ito, indicating that Ito is Ca2+-dependent K+ current. On the other hand, Iinfin was Ca2+-independent. Both Ito and Iinfin were completely inhibited by internal Cs+ and external TEA. The estimated reversal potential of Ito was close to the theoretical EK. Taken together, both outward currents were carried by K+ channels. From these results, Ito is likely to be a current responsible for the hyperpolarizing responses seen in hamster eggs at fertilization.

Fluoxetine inhibits L-type Ca2+ and transient outward K+ currents in rat ventricular myocytes

The most common cardiovascular side effects of antidepressants are cardiac arrhythmias and orthostatic hypotension. Little is known, however, about the mechanisms by which these adverse reactions may occur, especially with regard to newer drugs such as fluoxetine. We hypothesized that these side effects may have an electrophysiological basis at the level of the cardiac myocyte. Thus, we investigated the effects of fluoxetine and other antidepressants on action potentials and ionic currents of rat ventricular myocytes using the amphotericin B perforated patch clamp technique. Fluoxetine (10 microM) prolonged the action potential duration (APD50) to 146.7 +/- 12.9% of control value without altering resting membrane potential. Fluoxetine and sertraline potently inhibited the L-type Ca2+ current (IC50 = 2.82 and 2.31 microM, respectively), but did not significantly modify the steady-state inactivation. Amitriptyline and imipramine had similar, but slightly weaker, effects (IC50 = 3.75 and 4.05 microM, respectively). Fluoxetine attenuated the peak transient outward K+ current and also altered current kinetics, as shown by accelerated decay. Fluoxetine did not change the voltage-dependence of the steady-state inactivation. Sertraline, amitriptyline and imipramine inhibited the transient outward K+ current with potencies very similar to fluoxetine. In contrast to the other antidepressants tested, trazodone weakly inhibited the Ca2+ and K+ currents and moclobemide had no detectable effect. Our comparative pharmacology data suggest that selective serotonin reuptake inhibitors, such as fluoxetine, are as potent as tricyclic antidepressants in inhibiting L-type Ca2+ and transient outward K+ currents. These inhibitory effects may contribute to cardiovascular complications such as arrhythmias and orthostatic hypotension.

Modulation of outward potassium currents by nitric oxide in longitudinal smooth muscle cells of guinea-pig ileum

To investigate the possible involvement of outward potassium (K+) currents in nitric oxide-induced relaxation in intestinal smooth muscle, we used whole-cell patch clamp technique in freshly dispersed guinea-pig ileum longitudinal smooth muscle cells. When cells were held at -60 mV and depolarized from - 40 mV to + 50 mV in 10 mV increments, sustained outward K+ currents were evoked. The outward K+ currents were markedly increased by the addition of 10 muM sodium nitroprusside (SNP). 10 muM S-nitroso-N-acetylpenicillamine (SNAP) and 1 mM 8-Bromo-cyclic GMP (8-Br-cGMP) also showed a similar effect to that of SNP. 1 mM tetraethylammonium (TEA) significantly reduced depolarization-activated outward K+ currents. SNP-enhanced outward K+ currents were blocked by the application of TEA. High EGTA containing pipette solution (10 mM) reduced the control currents and also inhibited the SNP-enhanced outward K+ currents. 5 mM 4-aminopyridine (4-AP) significantly reduced the control currents but showed no effect on SNP-enhanced outward K+ currents. 0.3 muM apamin and 10 muM glibenclamide showed no effect on SNP-enhanced outward K+ currents. 1 muM 1H-(1,2,4)oxadiazolo (4,3-a)quinoxaline-1-one (ODQ), a specific inhibitor of soluble guanylate cyclase, significantly blocked SNP-enhanced K+ currents. We conclude that NO donors activate the Ca2+-activated K+ channels in guinea-pig ileal smooth muscle via activation of guanylate cyclase.