Decreased inward rectifier and voltage-gated K⁺ currents of the right septal coronary artery smooth muscle cells in pulmonary arterial hypertensive rats

In vascular smooth muscle, K⁺ channels, such as voltage-gated K⁺ channels (Kv), inward-rectifier K⁺ channels (Kir), and big-conductance Ca²⁺-activated K⁺ channels (BK(Ca)), establish a hyperpolarized membrane potential and counterbalance the depolarizing vasoactive stimuli. Additionally, Kir mediates endothelium-dependent hyperpolarization and the active hyperemia response in various vessels, including the coronary artery. Pulmonary arterial hypertension (PAH) induces right ventricular hypertrophy (RVH), thereby elevating the risk of ischemia and right heart failure. Here, using the whole-cell patch-clamp technique, we compared Kv and Kir current densities (I(Kv) and I(Kir)) in the left (LCSMCs), right (RCSMCs), and septal branches of coronary smooth muscle cells (SCSMCs) from control and monocrotaline (MCT)-induced PAH rats exhibiting RVH. In control rats, (1) I(Kv) was larger in RCSMCs than that in SCSMCs and LCSMCs, (2) I(Kv) inactivation occurred at more negative voltages in SCSMCs than those in RCSMCs and LCSMCs, (3) I(Kir) was smaller in SCSMCs than that in RCSMCs and LCSMCs, and (4) I(BKCa) did not differ between branches. Moreover, in PAH rats, I(Kir) and I(Kv) decreased in SCSMCs, but not in RCSMCs or LCSMCs, and I(BKCa) did not change in any of the branches. These results demonstrated that SCSMC-specific decreases in I(Kv) and I(Kir) occur in an MCT-induced PAH model, thereby offering insights into the potential pathophysiological implications of coronary blood flow regulation in right heart disease. Furthermore, the relatively smaller I(Kir) in SCSMCs suggested a less effective vasodilatory response in the septal region to the moderate increase in extracellular K⁺ concentration under increased activity of the myocardium.

Possible mechanisms involved in the effect of the subchronic administration of rosuvastatin on endothelial function in rats with metabolic syndrome

Metabolic syndrome is a multifaceted condition associated with a greater risk of various disorders (e.g., diabetes and heart disease). In a rat model of metabolic syndrome, an acute in vitro application of rosuvastatin causes relaxation of aortic rings. Since the outcome of a subchronic rosuvastatin treatment is unknown, the present study explored its effect on acetylcholine-induced vasorelaxation of aortic rings from rats with metabolic syndrome. Animals were submitted to a 16-week treatment, including a standard diet, a cafeteria-style diet (CAF-diet), or a CAF-diet with daily rosuvastatin treatment (10 mg/kg). After confirming the development of metabolic syndrome in rats, aortic segments were extracted from these animals (those treated with rosuvastatin and untreated) and the acetylcholine-induced relaxant effect on the corresponding rings was evaluated. Concentration-response curves were constructed for this effect in the presence/absence of L-NAME, ODQ, KT 5823, 4-aminopyridine (4-AP), tetraethylammonium (TEA), apamin plus charybdotoxin, glibenclamide, indomethacin, clotrimazole, and cycloheximide pretreatment. Compared to rings from control rats, acetylcholine-induced vasorelaxation decreased in rings from animals with metabolic syndrome, and was maintained at a normal level in animals with metabolic syndrome plus rosuvastatin treatment. The effect of rosuvastatin was inhibited by L-NAME, ODQ, KT 5823, TEA, apamin plus charybdotoxin, but unaffected by 4-AP, glibenclamide, indomethacin, clotrimazole, or cycloheximide. In conclusion, the subchronic administration of rosuvastatin to rats with metabolic syndrome improved the acetylcholine-induced relaxant response, involving stimulation of the NO/cGMP/PKG/Ca2+-activated K+ channel pathway.

Expression of potassium channel genes predicts clinical outcome in lung cancer

Lung cancer is the most common cause of cancer deaths worldwide and several molecular signatures have been developed to predict survival in lung cancer. Increasing evidence suggests that proliferation and migration to promote tumor growth are associated with dysregulated ion channel expression. In this study, by analyzing high-throughput gene expression data, we identify the differentially expressed K⁺ channel genes in lung cancer. In total, we prioritize ten dysregulated K⁺ channel genes (5 up-regulated and 5 down-regulated genes, which were designated as K-10) in lung tumor tissue compared with normal tissue. A risk scoring system combined with the K-10 signature accurately predicts clinical outcome in lung cancer, which is independent of standard clinical and pathological prognostic factors including patient age, lymph node involvement, tumor size, and tumor grade. We further indicate that the K-10 potentially predicts clinical outcome in breast and colon cancers. Molecular signature discovered through K⁺ gene expression profiling may serve as a novel biomarker to assess the risk in lung cancer.

Effect of extracellular potassium on the activity of distal renal tubule in mice / 上海交通大学学报（医学版）

Objective: To investigate the effect of extracellular potassium (K+) concentration on the activities of sodium chloride co-transporter (NCC) and large conductance Ca2+-activated K+ channel (BK) in distal renal tubule of mice. Methods: Six specific pathogen free (SPF) C57BL/6 mice aged 8 to 10 weeks were sacrificed,and the kidney slices were made with previously reported method. Then,these slices were incubated randomly in normal K+,high K+,BaCl2 and RbCl solutions,respectively. The abundance and phosphorylation level of NCC in kidney slices at different K+ concentrations and different time courses were detected by Western blotting. The overall and membrane expressions of BK in kidney slices were also detected after incubation with different K+ solutions for 2 h. Results: Compared with normal K+ solution,NCC phosphorylation level was significantly decreased after incubation with high K+ solution for 5,15,30 min (all P<0.05),and NCC phosphorylation level was also decreased after intervention with K+ channel inhibitor Ba2+ or Rb+ (both P<0.05). After the treatment with high K+ solution for 2 h,neither the overall cell expression of BKα subunit and β4 subunit,nor membrane expression of BKα subunit was found significant changes compared with normal K+ incubation. Conclusion: High K+ can directly down-regulate NCC phosphorylation level,which may be preparation for kaliuresis of the downstream tubule of distal convoluted tubule.

Construction of stable cell lines expressing large conductance Ca2+-activated K+ channel α-subunit and molecular mechanism of potassium excretion in this channel / 上海交通大学学报（医学版）

Objective: To construct stable cell lines expressing the large conductance Ca2+-activated K+ channel (MaxiK or BK) α-subunit and to explore the mechanism of potassium excretion via BKα channel. Methods:The BKα plasmid with Myc tag was constructed and transfected into HEK293 cell lines by lipofectamine 2000. The positive monoclonal cell lines were screened by G418, and the expression of BKα was detected by Western blotting and the location of BKα by immunofluorescence. The stable cell lines expressing BKα protein was cultured on slides to form a single cell layer, which was perfused with different potassium ion concentrations of 5 mmol/L and 100 mmol/L, and the single channel patch clamp recorded the ion flux of BKα. Wild type and mutants (G77R, G130R, C140R and R297C) of the inwardly rectifying potassium channel (Kir4.1) were transfected into HEK293 cells stably transfected with BKα, and then the membrane protein was extracted. The expression of BKα was detected by Western blotting. Results:Stable cell lines expressing BKα channel were selected from HEK293 cells after transfection and cellular immunofluorescence verified the expression of BKα channel and its expression on the cell membrane. The channel open frequency (Npo) of BKα increased rapidly when perfused with 100 mmol/L potassium. After being transfected with wild type or mutants of Kir4.1, the membrane expression of BKα in the stable cell lines showed significant difference among these groups (P<0.05). Conclusion:The HEK293 cell lines stably expressing BKα have been successfully constructed. BKα channel can be activated by high potassium solutions. The function of the BKα subunit can be related to Kir4.1 channel, which may be attributed to the depolarization of the cells transfected by Kir4.1 mutants.

Angiotensin (1-7) participating in renal fibrosis by inhibiting intermediate conductance Ca2+-activated K+ channels protein expression / 解剖学报

Objective: To investigate the relationship between the protective effect of angiotensin (Ang) (1-7) and the protein expression of intermediate conductance Ca2+-activated K+ channels (KCa3. 1) in renal fibrosis. Methods: Totally 60 male mice were randomly divided into 5 groups: control group (WT); Ang II group: mice received Ang II [1.4 mg/(kg.d)] by hypodermic injection; Ang II blocker group (Losartan): mice received Ang II [1.4 mg/(kg.d)] and Losartan [40 mg/(kg.d)]by hypodermic injection; Ang (1-7) group; mice received Ang II [1.4 mg/(kg.d)] and Ang (1-7) [0. 14 mg/(kg.d)] by hypodermic injection; diminazene aceturate(DIZE) group: mice received Ang II [1.4 mg/(kg.d)] and DIZE [10 mg/(kg.d)] by hypodermic injection. After 4 weeks of continuous administration, the related indicators were detected. Masson staining was used to detect the collagen content, and Western blotting was used to detect the protein expression of collagen type I, collagen type DI and KCa3. 1 channel. Results: Collagen deposition in renal tissue increased significantly after 4 weeks of hypodermic injection of Ang II (n = 12,P<0.01) compared with the WT group, which suggested that the model of renal fibrosis was successfully reproduced. Ang II significantly increased the synthesis of collagen type I and DI (n=6,P<0.01) and increased the expression of Kca3. 1 channel protein (n=6,P< 0. 01) in renal tissues, while Ang (1-7) and ACE2 activator DIZE significantly inhibited those exchanges (n= 12 or 6,P< 0. 01). Conclusion: Ang (1-7) plays a protective role in the process of renal fibrosis, which may be related to the downregulation of KCa3. 1 channel protein expression in renal tissue.

Polysaccharide extracts of Astragalus membranaceus and Atractylodes macrocephala promote intestinal epithelial cell migration by activating the polyamine-mediated K channel / 中国天然药物

Astragalus membranaceus (Radix Astragali, RA) and Atractylodes macrocephala (Rhizoma Atractylodis Macrocephalae, RAM) are often used to treat gastrointestinal diseases. In the present study, we determined the effects of polysaccharides extracts from these two herbs on IEC-6 cell migration and explored the potential underlying mechanisms. A migration model with IEC-6 cells was induced using a single-edged razor blade along the diameter of cell layers in six-well polystyrene plates. The cells were grown in control media or media containing spermidine (5 μmol·L, SPD), alpha-difluoromethylornithine (2.5 mmol·L, DFMO), 4-Aminopyridine (40 μmol·L, 4-AP), the polysaccharide extracts of RA or RAM (50, 100, or 200 mg·L), DFMO plus SPD, or DFMO plus polysaccharide extracts of RA or RAM for 12 or 24 h. Next, cytosolic free Ca ([Ca]) was measured using laser confocal microscopy, and cellular polyamine content was quantified with HPLC. Kv1.1 mRNA expression was assessed using RT-qPCR and Kv1.1 and RhoA protein expressions were measured with Western blotting analysis. A cell migration assay was carried out using Image-Pro Plus software. In addition, GC-MS was introduced to analyze the monosaccharide composition of both polysaccharide extracts. The resutls showed that treatment with polysaccharide extracts of RA or RAM significantly increased cellular polyamine content, elevated [Ca] and accelerated migration of IEC-6 cells, compared with the controls (P < 0.01). Polysaccharide extracts not only reversed the inhibitory effects of DFMO on cellular polyamine content and [Ca], but also restored IEC-6 cell migration to control level (P < 0.01 or < 0.05). Kv1.1 mRNA and protein expressions were increased (P < 0.05) after polysaccharide extract treatment in polyamine-deficient IEC-6 cells and RhoA protein expression was increased. Molar ratios of D-ribose, D-arabinose, L-rhamnose, D-mannose, D-glucose, and D-galactose was 1.0 : 14.1 : 0.3 : 19.9 : 181.3 : 6.3 in RA and 1.0 : 4.3 : 0.1 : 5.7 : 2.8 : 2.2 in RAM. In conclusion, treatment with RA and RAM polysaccharide extracts stimulated migration of intestinal epithelial cells via a polyamine-Kv1.1 channel activated signaling pathway, which facilitated intestinal injury healing.

Polysaccharide extracts of Astragalus membranaceus and Atractylodes macrocephala promote intestinal epithelial cell migration by activating the polyamine-mediated K channel / 中国天然药物

Astragalus membranaceus (Radix Astragali, RA) and Atractylodes macrocephala (Rhizoma Atractylodis Macrocephalae, RAM) are often used to treat gastrointestinal diseases. In the present study, we determined the effects of polysaccharides extracts from these two herbs on IEC-6 cell migration and explored the potential underlying mechanisms. A migration model with IEC-6 cells was induced using a single-edged razor blade along the diameter of cell layers in six-well polystyrene plates. The cells were grown in control media or media containing spermidine (5 μmol·L, SPD), alpha-difluoromethylornithine (2.5 mmol·L, DFMO), 4-Aminopyridine (40 μmol·L, 4-AP), the polysaccharide extracts of RA or RAM (50, 100, or 200 mg·L), DFMO plus SPD, or DFMO plus polysaccharide extracts of RA or RAM for 12 or 24 h. Next, cytosolic free Ca ([Ca]) was measured using laser confocal microscopy, and cellular polyamine content was quantified with HPLC. Kv1.1 mRNA expression was assessed using RT-qPCR and Kv1.1 and RhoA protein expressions were measured with Western blotting analysis. A cell migration assay was carried out using Image-Pro Plus software. In addition, GC-MS was introduced to analyze the monosaccharide composition of both polysaccharide extracts. The resutls showed that treatment with polysaccharide extracts of RA or RAM significantly increased cellular polyamine content, elevated [Ca] and accelerated migration of IEC-6 cells, compared with the controls (P < 0.01). Polysaccharide extracts not only reversed the inhibitory effects of DFMO on cellular polyamine content and [Ca], but also restored IEC-6 cell migration to control level (P < 0.01 or < 0.05). Kv1.1 mRNA and protein expressions were increased (P < 0.05) after polysaccharide extract treatment in polyamine-deficient IEC-6 cells and RhoA protein expression was increased. Molar ratios of D-ribose, D-arabinose, L-rhamnose, D-mannose, D-glucose, and D-galactose was 1.0 : 14.1 : 0.3 : 19.9 : 181.3 : 6.3 in RA and 1.0 : 4.3 : 0.1 : 5.7 : 2.8 : 2.2 in RAM. In conclusion, treatment with RA and RAM polysaccharide extracts stimulated migration of intestinal epithelial cells via a polyamine-Kv1.1 channel activated signaling pathway, which facilitated intestinal injury healing.

Beneficial Effect of Berberis amurensis Rupr. on Penile Erection / 中国结合医学杂志

<p><b>OBJECTIVE</b>To investigate whether the methanol extract of Berberis amurensis Rupr. (BAR) augments penile erection using in vitro and in vivo experiments.</p><p><b>METHODS</b>The ex vivo study used corpus cavernosum strips prepared from adult male New Zealand White rabbits. In in vivo studies for intracavernous pressure (ICP), blood pressure, mean arterial pressure (MAP), and increase of peak ICP were continuously monitored during electrical stimulation of Sprague-Dawley rats.</p><p><b>RESULTS</b>Preconstricted with phenylephrine (PE) in isolated endotheliumintact rabbit corus cavernosum, BAR relaxed penile smooth muscle in a dose-dependent manner, which was inhibited by pretreatment with NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, and H-[1,2,4]-oxadiazole-[4,3-α]-quinoxalin-1-one, a soluble guanylyl cclase inhibitor. BAR significantly relaxed penile smooth muscles dose-dependently in ex vivo, and this was inhibited by pretreatment with L-NAME H-[1,2,4]-oxadiazole-[4,3-α]-quinoxalin-1-one. BAR-induced relaxation was significantly attenuated by pretreatment with tetraethylammonium (TEA, P<0.01), a nonselective K channel blocker, 4-aminopyridine (4-AP, P<0.01), a voltage-dependent K channel blocker, and charybdotoxin (P<0.01), a large and intermediate conductance Ca sensitive-K channel blocker, respectively. BAR induced an increase in peak ICP, ICP/MAP ratio and area under the curve dose dependently.</p><p><b>CONCLUSION</b>BAR augments penile erection via the nitric oxide/cyclic guanosine monophosphate system and Ca sensitive-K (BK and IK) channels in the corpus cavernosum.</p>

Overexpression of K+ channel regulator inhibits proliferation, migration and invasion of hepatocellular carcinoma cells / 肿瘤

Objective: To detect the expression level of K+ channel regulator (KCNRG) in hepatocellular carcinoma (HCC) cells, and further to investigate the effects of up-regulation of KCNRG gene expression on the proliferation, colony formation, migration, invasion and epithelial-tomesenchymal transition (EMT) of HCC cells. Methods: The expression levels of KCNRG mRNA and protein in human immortalized normal liver cell line THLE-3 and HCC cell lines including BEL-7402, SMMC-7721, MHCC-LM3 and SK-HEP1 were detected by RT-PCR, real-time fluorescent quantitative PCR and Western blotting, respectively. The KCNRG gene overexpression vector KCNRG-pcDNA3.1 (+) was transfected into HCC MHCC-LM3 and SK-HEP1 cells by using LipofectAMINE 2000, while the corresponding empty vector-transfection group and untransfection group were used as the negative control and blank control, respectively. The efficiency of KCNRG overexpression was verified by real-time fluorescent quantitative PCR and Western blotting, respectively. Then the expression levels of EMT markers in MHCC-LM3 and SK-HEP1 cells with KCNRG overexpression were detected by Western blotting. The changes of proliferation, colony formation, migration and invasion abilities of the transfected MHCC-LM3 and SK-HEP1 cells were detected by cytometry, clone forming assay, Transwell chamber assay, respectively. Results: Compared with the human immortalized normal liver cell line THLE-3, the expression levels of KCNRG mRNA and protein were higher than those in HCC cells, especially in MHCC-LM3 and SK-HEP1 cells (both P < 0.01). After transfection of KCNRG-pcDNA3.1 (+), the expression of KCNRG gene was up-regulated in MHCC-LM3 and SK-HEP1 cells (both P < 0.01). The expression level of N-cadherin was significantly decreased in KCNRG gene overexpressed MHCC-LM3 and SK-HEP1 cells (both P < 0.01), while the expression level of E-cadherin was significantly increased (both P < 0.01). The proliferation, colony formation, migration and invasion abilities of MHCC-LM3 and SK-HEP1 cells were significantly inhibited after KCNRG overexpression (all P < 0.01). Conclusion: The expression level of KCNRG gene in HCC cells was lower than that in human normal liver cells. The up-regulation of KCNRG gene expression can reduce the proliferation, colony formation, migration, invasion and EMT of HCC cells.

Inhibition of voltage-dependent K⁺ current in rabbit coronary arterial smooth muscle cells by the class Ic antiarrhythmic drug propafenone

In this study, we demonstrated the inhibitory effect of the Class Ic antiarrhythmic agent propafenone on voltage-dependent K⁺ (Kv) channels using freshly isolated coronary artery smooth muscle cells from rabbits. The Kv current amplitude was progressively inhibited by propafenone in a dose-dependent manner, with an apparent IC₅₀ value of 5.04±1.05 µM and a Hill coefficient of 0.78±0.06. The application of propafenone had no significant effect on the steady-state activation and inactivation curves, indicating that propafenone did not affect the voltage-sensitivity of Kv channels. The application of train pulses at frequencies of 1 or 2 Hz progressively increased the propafenone-induced inhibition of the Kv current. Furthermore, the inactivation recovery time constant was increased after the application of propafenone, suggesting that the inhibitory action of propafenone on Kv current is partially use-dependent. Pretreatment with Kv1.5, Kv2.1 or Kv7 inhibitor did not change the inhibitory effect of propafenone on the Kv current. Together, these results suggest that propafenone inhibits the vascular Kv channels in a dose- and use-dependent manner, regardless of Na⁺ channel inhibition.

Antidepressant drug paroxetine blocks the open pore of Kv3.1 potassium channel

In patients with epilepsy, depression is a common comorbidity but difficult to be treated because many antidepressants cause pro-convulsive effects. Thus, it is important to identify the risk of seizures associated with antidepressants. To determine whether paroxetine, a very potent selective serotonin reuptake inhibitor (SSRI), interacts with ion channels that modulate neuronal excitability, we examined the effects of paroxetine on Kv3.1 potassium channels, which contribute to highfrequency firing of interneurons, using the whole-cell patch-clamp technique. Kv3.1 channels were cloned from rat neurons and expressed in Chinese hamster ovary cells. Paroxetine reversibly reduced the amplitude of Kv3.1 current, with an IC₅₀ value of 9.43 µM and a Hill coefficient of 1.43, and also accelerated the decay of Kv3.1 current. The paroxetine-induced inhibition of Kv3.1 channels was voltage-dependent even when the channels were fully open. The binding (k₊₁) and unbinding (k₋₁) rate constants for the paroxetine effect were 4.5 µM⁻¹s⁻¹ and 35.8 s⁻¹, respectively, yielding a calculated K(D) value of 7.9 µM. The analyses of Kv3.1 tail current indicated that paroxetine did not affect ion selectivity and slowed its deactivation time course, resulting in a tail crossover phenomenon. Paroxetine inhibited Kv3.1 channels in a usedependent manner. Taken together, these results suggest that paroxetine blocks the open state of Kv3.1 channels. Given the role of Kv3.1 in fast spiking of interneurons, our data imply that the blockade of Kv3.1 by paroxetine might elevate epileptic activity of neural networks by interfering with repetitive firing of inhibitory neurons.

Mitochondrial dysfunction reduces the activity of KIR2.1 K⁺ channel in myoblasts via impaired oxidative phosphorylation

Myoblast fusion depends on mitochondrial integrity and intracellular Ca²⁺ signaling regulated by various ion channels. In this study, we investigated the ionic currents associated with [Ca²⁺]i regulation in normal and mitochondrial DNA-depleted (ρ0) L6 myoblasts. The ρ0 myoblasts showed impaired myotube formation. The inwardly rectifying K⁺ current (I(Kir)) was largely decreased with reduced expression of KIR2.1, whereas the voltage-operated Ca²⁺ channel and Ca²⁺-activated K⁺ channel currents were intact. Sustained inhibition of mitochondrial electron transport by antimycin A treatment (24 h) also decreased the I(Kir). The ρ0 myoblasts showed depolarized resting membrane potential and higher basal [Ca²⁺]ᵢ. Our results demonstrated the specific downregulation of I(Kir) by dysfunctional mitochondria. The resultant depolarization and altered Ca²⁺ signaling might be associated with impaired myoblast fusion in ρ0 myoblasts.

Effect of four 5-hydroxytryptamine type 4 receptor agonists on rat cardiac Iκ1 channels and proarrhythmic risk stratification / 中国药理学与毒理学杂志

OBJECTIVE To compare the effect of four 5-hydroxytryptamine type 4 (5-HT4) receptor agonists:cisapride,zacopride,macopride and 2-[1-(4-piperonyl) piperazinyl]-benzothiazole (BZTZ),on rat cardiac inward rectifier potassium channel (IK1)and heart rhythm.METHODS The whole-cell configuration of patch-clamp technique was used to record effects of 5-HT4 receptor agonists onIk1 in enzymatic dissociated rat ventricular myocytes or Kir2.1 transfected HEK 293 cells.Western blotting was used to observe the expression of Kir2.1 channel exposed 24 h to agents in ventricular myocytes.Langendorff-perfused hearts were perfused with four agents respectively for 30 min.The electrocardiogram was recorded simultaneously.RESULTS BZTZ,cisapride and mosapride 0.1-10 μmol· L-1 decreasedIk1 in a concentrationdependent manner.At the same concentration (1 μmol· L-1),BZTZ showed the most potent inhibition onIκ1 (P＜0.01),followed by cisapride.Mosapride showed slight inhibition efficiency.However,zacopride enhanced Iκ1 (P＜0.01).In Kir2.1 heterologous expression systems,zacopride activated Kir2.1 current (P＜0.01) while mosapride had no effect.In ex vivo Langendorff-perfused hearts,BZTZ and cisapride 1μmol· L-1 elicited singnificant rhythm disturbances,and the total of premature ventricular beats (PVB) were 159±28 and 61±13.50％ (4/8) (P＜0.05) and 25％ (1/8) of the hearts exhibited ventricular tachycardia (VT),while 37.5％ (3/8) and 12.5％ (1/8) of the hearts exhibited ventricular fibrillation (VF),respectively.Mosapride and zacopride had no side effects on heart rhythm.Zacopride also suppressed BZTZ-or cisapride-induced arrhythmias.BZFZ had the strongest proarryhthmic potency among the 5-HT4 agonists,followed by cisapride,mosapride and zacopride.CONCLUSION Iκ1 might be an independent risk factor for arrhythmogenesis and a new target for screening safe 5-HT4 receptor agonists and gastrointestinal prokinetic agents.

Intermediate-conductance Ca2+-activated K+channel:research advances / 国际药学研究杂志

Intermediate-conductance Ca2+-activated K+channel ,also known as KCa3.1,IKCa and SK4,is widely distributed in fibroblasts,proliferating smooth muscle cells,endothelial cells,T lymphocytes,plasma cells,macrophages,and epithelial cells, and involved in the pathological and physiological processes such as vascular contraction,inflammation ,calcification,tissue fibrosis, immune response,malignant tumor,internal and external secretory glands. In recent years,it has been found that blocking the KCa3.1 pathway or knockouting the gene can significantly prevent the pathophysiological process of its involvement. The recent use of the specific blocker TRAM-34 in animals and humans shows its safety and tolerability,providing a new direction for the treatment of related diseases. In this article,the research progress in KCa3.1 related diseases in recent years is reviewed.

Intermediate-conductance Ca2+-activated K+ channel: Research advances / 国际药学研究杂志

Intermediate-conductance Ca2+-activated K+ channel, also known as KCa3.1, IKCa and SK4, is widely distributed in fibroblasts, proliferating smooth muscle cells, endothelial cells, T lymphocytes, plasma cells, macrophages, and epithelial cells, and involved in the pathological and physiological processes such as vascular contraction, inflammation, calcification, tissue fibrosis, immune response, malignant tumor, internal and external secretory glands. In recent years, it has been found that blocking the KCa3.1 pathway or knockouting the gene can significantly prevent the pathophysiological process of its involvement. The recent use of the specific blocker TRAM-34 in animals and humans shows its safety and tolerability, providing a new direction for the treatment of related diseases. In this article, the research progress in KCa3.1 related diseases in recent years is reviewed.

T wave

The T wave in a surface electrocardiogram (ECG) indicates the diastolic phase in the cardiac cycle. Even though the cellular basis of T-wave morphology in surface ECG remains unclear in clinical cardiology, the morphology may be determined by the transmural voltage gradient during the repolarization period that underlies the changes in the T wave and QT interval. The heterogeneous distribution of electrophysiological activity across the heart is essential for normal cardiac function. However, excessive heterogeneity may contribute to arrhythmogenesis and sudden cardiac death. This paper will provide an overview of T wave genesis and the contribution to action potential duration (APD), in which ion channels are involved in the repolarization period, with special emphasis on K+ channels involved in phase 3 repolarization. These channels are primarily Kv11.1 (hERG1), Kv7.1 (KCNQ1), and Kir2.1 (KCNJ2), which are the α-subunits responsible for conducting I(Kr), I(Ks), and I(K1). Changes in the T wave and QT interval that are affected by both functional loss and gain of these currents are associated with various arrhythmogenic diseases. This review also briefly discusses arrhythmogenesis in diseases that are manifested by changes in the T wave and QT interval.

Nortriptyline, a tricyclic antidepressant, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We demonstrated the effect of nortriptyline, a tricyclic antidepressant drug and serotonin reuptake inhibitor, on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Nortriptyline inhibited Kv currents in a concentration-dependent manner, with an apparent IC₅₀ value of 2.86±0.52 µM and a Hill coefficient of 0.77±0.1. Although application of nortriptyline did not change the activation curve, nortriptyline shifted the inactivation current toward a more negative potential. Application of train pulses (1 or 2 Hz) did not change the nortriptyline-induced Kv channel inhibition, suggesting that the effects of nortiprtyline were not use-dependent. Preincubation with the Kv1.5 and Kv2.1/2.2 inhibitors, DPO-1 and guangxitoxin did not affect nortriptyline inhibition of Kv channels. From these results, we concluded that nortriptyline inhibited Kv channels in a concentration-dependent and state-independent manner independently of serotonin reuptake.

Chronic Ca²⁺ influx through voltage-dependent Ca²⁺ channels enhance delayed rectifier K⁺ currents via activating Src family tyrosine kinase in rat hippocampal neurons

Excessive influx and the subsequent rapid cytosolic elevation of Ca²⁺ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic Ca²⁺ level in normal as well as pathological conditions. Delayed rectifier K⁺ channels (I(DR) channels) play a role to suppress membrane excitability by inducing K⁺ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under Ca²⁺-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of IDR channels to hyperexcitable conditions induced by high Ca²⁺ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high Ca²⁺-treatment significantly increased the amplitude of IDR without changes of gating kinetics. Nimodipine but not APV blocked Ca²⁺-induced IDR enhancement, confirming that the change of I(DR) might be targeted by Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated I(DR) enhancement was not affected by either Ca²⁺-induced Ca²⁺ release (CICR) or small conductance Ca²⁺-activated K⁺ channels (SK channels). Furthermore, PP2 but not H89 completely abolished I(DR) enhancement under high Ca²⁺ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for Ca²⁺-mediated I(DR) enhancement. Thus, SFKs may be sensitive to excessive Ca²⁺ influx through VDCCs and enhance I(DR) to activate a neuroprotective mechanism against Ca²⁺-mediated hyperexcitability in neurons.

Escitalopram, a selective serotonin reuptake inhibitor, inhibits voltage-dependent K⁻ channels in coronary arterial smooth muscle cells

We investigated the inhibitory effect of escitalopram, a selective serotonin reuptake inhibitor (SSRI), on voltage-dependent K⁺ (Kv) channels in freshly separated from rabbit coronary arterial smooth muscle cells. The application of escitalopram rapidly inhibited vascular Kv channels. Kv currents were progressively inhibited by an increase in the concentrations of escitalopram, suggesting that escitalopram inhibited vascular Kv currents in a concentration-dependent manner. The IC₅₀ value and Hill coefficient for escitalopram-induced inhibition of Kv channels were 9.54±1.33 µM and 0.75±0.10, respectively. Addition of escitalopram did not alter the steady-state activation and inactivation curves, suggesting that the voltage sensors of the channels were not affected. Pretreatment with inhibitors of Kv1.5 and/or Kv2.1 did not affect the inhibitory action of escitalopram on vascular Kv channels. From these results, we concluded that escitalopram decreased the vascular Kv current in a concentration-dependent manner, independent of serotonin reuptake inhibition.