Voltage-dependent Potassium Channel Blocker Research Articles

The effect of fampridine on gait in people with Multiple sclerosis (MS)

Fampridineis a drug for people with Multiple Sclerosis (MS). It is a broad-spectrum voltage-dependent potassium channel blocker that enhances synaptic transmission. The drug has been shown to be able to enhance conduction in demyelinated axons, thereby leading to improved gait in patients withMS. The purpose of this study was to examine the effect of fampridine on gait function in people with MS in the end of a 2 weeks trial drug period and to observe how many patients continued drug therapy. Data from 41 individuals with MS was collected retrospectively for this study. Measurements were administered by physiotherapists and the results from the Timed 25-Foot Walk (T25FW) and 12-item Multiple Sclerosis Walking Scale (MSWS-12) were obtained from medical records from The National University Hospital of Iceland. The results showed a significant difference in walking speed before and at the end of trial period (p<0.0001). The average improvement in walking speed was 22%. Results also demonstrated a significant difference in MSWS-12 scores before and at the end of treatment (p<0.0001). The average improvement in MSWS-12 was 11.4 points. Eighteen individuals (43.9%) continued treatment after the trial period. Fampridine can have a positive effect on impaired gait function in people with MS and can be an important adjunct to treatment.

The Repression of Matrix Metalloproteinases and Cytokine Secretion in Glioblastoma by Targeting K+ Channel.

Introduction:Glioblastoma is an aggressive human brain malignancy with poorly understood pathogenesis. Voltage-gated potassium (Kv) channels and Matrix Metalloproteinases (MMPs) are highly expressed in malignant tumors and involved in the progression and metastasis of glioblastoma. This study aimed to determine whether a voltage-dependent potassium channel blocker could modulate astrocytes as a cell involved in the immunopathogenesis of glioblastoma.Methods:The cytotoxic effect of 4-Aminopyridine (4-AP) at different doses in the cell model of glioblastoma was measured by MTT assay. The ELISA technique and gelatin zymography were used to assess cytokine levels and MMP-9 after 4-AP treatment.Results:Cytotoxicity analysis data indicated that cell viability reduced by increasing 4-AP level and cell growth decreased gradually by removing 4-AP from the cell medium. 4-AP inhibits the secretion of IL-6 and IL-1 (P<0.05). MMP9 activity significantly inhibits with increased 4-AP dose, compared to non-treated cells.Conclusion:The reduction of cell viability, IL-6 secretion, and MMP-9 activity in an in vitro model of glioblastoma might be assumed 4-AP as an agent for chemoprevention of cancer.Highlights4-Aminopyridine, as a K channel blocker, inhibits the secretion of IL-1.A voltage-gated potassium channel inhibits the secretion of IL-6.MMP9 activity, as a tumor metastasis marker, significantly decreased by 4-AP.Plain Language SummaryGlioblastoma is the most common primary malignant of the brain, which remains mainly untreatable. A group of enzymes -matrix metalloproteinases- can digest various extracellular matrix macromolecules. They express at a high level and play a role in the glioblastoma invasion. Besides, several substances are secreted by multiple cells and affect cancer metastasis. Among them, cytokines, like interleukin-6, released from glial cells, may contribute to glioblastoma progression. The present study determined whether an agent as a potassium channel blocker could modulate the immunopathogenesis of glioblastoma. We realized the cytotoxic effect of potassium channel blocker at different doses in the U-373 MG glioblastoma astrocytoma cells. Our chosen agent inhibits the secretion of both interleukin and matrix metalloproteinases activity. Overall, we suggest potassium channel blocker as an agent for cancer chemoprevention.

Evaluating dalfampridine for the treatment of relapsing-remitting multiple sclerosis: does it add to the treatment armamentarium?

ABSTRACTIntroduction: Multiple sclerosis (MS) is a demyelinating disease, causing axonal damage and disability. Dalfampridine (DAL) is an extended-release formulation of 4-aminopyridine (4AP) and broad-spectrum voltage-dependent potassium channel blocker that is reported to improve motor, visual and cognitive functions. Furthermore, it is presently the only approved drug for walking impairment in MS.Areas covered: Herein, the authors evaluate DAL as a relapsing-remitting MS treatment, reporting and commenting on all aspects of the drug including its chemistry, safety, pharmacokinetics, and cost-effectiveness. A bibliographic search was performed on PubMed using the terms ‘dalfampridine OR fampridine OR 4-aminopyridine’.Expert opinion: Evidence from post-marketing studies suggests that DAL, consistent with the effects of 4AP, may not only improve walking speed, but also arm function, fatigue, mood and cognition through restored nerve conduction in central nervous system demyelinated areas. Long-term safety data confirm that the approved dose of 10 mg twice daily is generally well tolerated. However, despite the reported efficacy, the extent of the benefits is limited in real life activities, although significant improvements have been demonstrated in the clinical setting. Patients often complain of side effects (such as cramps and painful paraesthesia) or lack of efficacy. Also, its considerably higher pricing in comparison to 4AP represents an important limitation.

Effect of tolbutamide on tetraethylammonium-induced postsynaptic zinc signals at hippocampal mossy fiber-CA3 synapses.

The application of tetraethylammonium (TEA), a blocker of voltage-dependent potassium channels, can induce long-term potentiation (LTP) in the synaptic systems CA3-CA1 and mossy fiber-CA3 pyramidal cells of the hippocampus. In the mossy fibers, the depolarization evoked by extracellular TEA induces a large amount of glutamate and also of zinc release. It is considered that zinc has a neuromodulatory role at the mossy fiber synapses, which can, at least in part, be due to the activation of presynaptic ATP-dependent potassium (KATP) channels. The aim of this work was to study properties of TEA-induced zinc signals, detected at the mossy fiber region, using the permeant form of the zinc indicator Newport Green. The application of TEA caused a depression of those signals that was partially blocked by the KATP channel inhibitor tolbutamide. After the removal of TEA, the signals usually increased to a level above baseline. These results are in agreement with the idea that intense zinc release during strong synaptic events triggers a negative feedback action. The zinc depression, caused by the LTP-evoking chemical stimulation, turns into potentiation after TEA washout, suggesting the existence of a correspondence between the observed zinc potentiation and TEA-evoked mossy fiber LTP.

Real-life experience with fampridine (Fampyra®) for patients with multiple sclerosis and gait disorders.

Fampridine is a broad-spectrum voltage-dependent potassium channel blocker that enhances synaptic transmission. The drug has been shown to be able to ameliorate conduction in demyelinated axons, thereby leading to improved gait in patients with multiple sclerosis (MS). To assess the "real-life" efficacy and safety of fampridine prescribed for gait disorders in MS. This was an observational and prospective study carried out at MS Units participating in the Brazilian Multiple Sclerosis Study Group. Patients with MS and gait disorders were prescribed fampridine (10 mg twice a day), irrespectively of the degree of disability determined by MS. Neurological disability determined by MS was assessed with the expanded disability scale score (EDSS). Outcomes for efficacy and safety of the drug were evaluated by the 25 foot-walk test and by the adverse events of fampridine. The time taken to walk 25 feet decreased by 20% or more in 62 patients (70%). Twenty-five patients were considered to be non-responders to this treatment. Improvement in walking speed was independent of improvement of disability. Mild or moderate adverse events were reported in 8% of patients. Fampridine is an efficient and safe therapeutic option for patients with MS and gait disorders.

Exogenous H2 S enhances mice gastric smooth muscle tension through S-sulfhydration of KV 4.3, mediating the inhibition of the voltage-dependent potassium current.

Hydrogen sulfide (H2 S) has been shown to have an excitatory effect on gastric motility, but the underlying molecular mechanism is unclear. In this study, we aimed to investigate the possible targets of H2 S and determine how H2 S affects its target proteins during H2 S-induced contraction. Patch-clamp and potentiometric fluorescence dye were utilized to measure the electrophysiological changes. The Biotin-switch assay was utilized to detect the protein S-sulfhydration. The isometric tension measurement was conducted too. Exogenous H2 S enhanced the tonic contraction of gastric antral smooth muscle, and voltage-dependent potassium channel (KV ) blocker and Dithiothreitol (DTT, a reducing agent) abolished the excitatory effect of NaHS. Exogenous H2 S inhibited the fast inactivation component of the voltage-dependent potassium channel current (IKVfast ) in isolated gastric antral smooth muscle cells. H2 S inhibited the KV 4.3 current in H293 cells with heterologous expression of KV 4.3, but did not inhibit the KV 4.1 and KV 4.2 currents, which together contribute greatly to IKVfast . NaHS significantly decreased the membrane potential in cultured gastric smooth muscle cells, but the NaHS-induced depolarization was suppressed by knockdown of KV 4.3 and N-ethylamaleimide (NEM), a free thiol group blocker. In addition, NaHS sulfhydrated KV 4.3 in H293 cells and in gastric smooth muscle tissue. However, this S-sulfhydration was inhibited by NEM and DTT. Meanwhile the NaHS-induced inhibition of IKVfast and KV 4.3 was also blocked by NEM and DTT. These results suggest that exogenous H2 S sulfhydrates KV 4.3 to decrease the membrane potential, thereby enhancing the basal tension of gastric antral smooth muscle.

Dalfampridine may activate latent trigeminal neuralgia in patients with multiple sclerosis.

To determine the effect of dalfampridine (4-aminopyridine), a broad-spectrum, voltage-dependent potassium channel blocker, on patients with trigeminal nerve dysfunction due to multiple sclerosis (MS). We reviewed histories of 71 patients in our clinic with clinically definite MS who were treated with dalfampridine for at least 2 to 3 months. Of the 71 patients, 5 had a history of either trigeminal neuralgia or altered facial sensation. Of these 5 patients, 3 with preexisting trigeminal neuralgia had a marked worsening of facial pain in close proximity to starting dalfampridine. One patient with altered facial sensation developed trigeminal pain after being on dalfampridine for 18 months. Pain in this individual rapidly subsided when dalfampridine was discontinued. Pain in the worsened 3 patients persisted, became more refractory to previously effective medications, and in one instance required trigeminal surgery for pain control. Dalfampridine should be used with caution in persons with trigeminal neuralgia due to MS. This study provides Class IV evidence that treatment with dalfampridine may precipitate or exacerbate preexisting trigeminal neuralgia.

The concomitant coronary vasodilator and positive inotropic actions of the nitroxyl donor Angeli's salt in the intact rat heart: contribution of soluble guanylyl cyclase‐dependent and ‐independent mechanisms

The NO redox sibling nitroxyl (HNO) elicits soluble guanylyl cyclase (sGC)-dependent vasodilatation. HNO has high reactivity with thiols, which is attributed with HNO-enhanced left ventricular (LV) function. Here, we tested the hypothesis that the concomitant vasodilatation and inotropic actions induced by a HNO donor, Angeli's salt (sodium trioxodinitrate), were sGC-dependent and sGC-independent respectively. Haemodynamic responses to Angeli's salt (10 pmol-10 μmol), alone and in the presence of scavengers of HNO (L-cysteine, 4 mM) or of NO [hydroxocobalamin (HXC), 100 μM] or a selective inhibitor of sGC [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), 10 μM], a CGRP receptor antagonist (CGRP8-37 , 0.1 μM) or a blocker of voltage-dependent potassium channels [4-aminopyridine (4-AP), 1 mM] were determined in isolated hearts from male rats. Angeli's salt elicited concomitant, dose-dependent increases in coronary flow and LV systolic and diastolic function. Both L-cysteine and ODQ shifted (but did not abolish) the dose-response curve of each of these effects to the right, implying contributions from HNO and sGC in both the vasodilator and inotropic actions. In contrast, neither HXC, CGRP8-37 nor 4-AP affected these actions. Both vasodilator and inotropic actions of the HNO donor Angeli's salt were mediated in part by sGC-dependent mechanisms, representing the first evidence that sGC contributes to the inotropic and lusitropic action of HNO in the intact heart. Thus, HNO acutely enhances LV contraction and relaxation, while concomitantly unloading the heart, potentially beneficial actions in failing hearts.

Functional expression of large-conductance Ca2+-activated potassium channels in lateral globus pallidus neurons

The presence of large-conductance Ca2+-activated potassium (BK) channels, which are considered to play an important role in the excitability of neurons, in the highly-excitable lateral globus pallidus (LGP) neurons has yet to be confirmed. In this study, we confirmed the functional expression of BK channels in mouse LGP neurons and investigated the characteristics of their single-channel currents using inside-out patch-clamp recordings. These BK channels had a conductance of 276 pS, were activated by the elevation of both the transmembrane potential and intracellular calcium concentration ([Ca2+]i), and were completely blocked by the BK channel-specific blocker paxilline (100 nM). In addition, the channel currents were sensitive to high-energy phosphate compounds and low internal pH. The cellular function of these BK channels was then investigated by nystatin-perforated whole-cell recording. Paxilline (100 nM) had no effect on the frequency and half-width of the action potential (AP) in LGP neurons under control conditions, but significantly attenuated the hyperpolarization that was caused by carbonyl cyanide m-chlorophenylhydrazone (CCCP), an inhibitor of ATP synthesis. In addition, the pancreatic β-cell type ATP-sensitive potassium channel (KATP channel) blocker tolbutamide (0.25 mM) also attenuated the hyperpolarization, in a manner similar to paxilline. The voltage-dependent potassium channel blocker tetraethylammonium (TEA, 2 mM) significantly decreased the frequency and increased the half-width of the AP in LGP neurons under control conditions, and attenuated CCCP-induced hyperpolarization to an extent close to that of paxilline. The results presented here suggest that functional BK channels are present in LGP neurons, and may behave as partners of KATP channels in the regulation of neuronal activity under metabolic stress conditions.

Voltage‐dependent potassium currents of novel threadlike structure on the surface of internal organs in rats

The electrophysiological properties of novel threadlike structure (NTS) on the surface of internal organs were investigated using whole cell patch clamp technique. NTS had well‐developed branches and were joined to a corpuscle (NTSC). Voltage clamp analysis revealed that the current‐voltage relationship (I–V) was highly non‐linear and can be divided into four types (Type I ~ IV) by slope conductance and their passive membrane properties in NTS cells. The outward current was inhibited, while residual currents were existed in outward and inward currents, by the voltage‐dependent potassium (Kv) channel blocker, tetraethylammonium (TEA), in a concentration‐dependent manner (IC50: 4.30 ± 1.71 and 4.43 ± 1.92 mM at +60 mV and −60 mV, respectively). These results indicated that the current was mainly carried by K+ ions. In addition, the resting membrane potential was depolarized by administration of 30 mM TEA. A systematic screening using RT‐PCR technique showed that genes of Kv1.2, Kv1.3, Kv2.1, Kv3.2, Kv3.3, Kv3.4, Kv4.1, Kv4.2 and Kv4.3 were expressed in NTSC. Taken together, our results indicated that Kv channel has an important role in regulating the membrane potential of NTSC cells.

Calcium oscillations induced by gambierol in cerebellar granule cells

Gambierol is a marine polyether ladder toxin derived from the dinoflagellate Gambierdiscus toxicus. To date, gambierol has been reported to act either as a partial agonist or as an antagonist of sodium channels or as a blocker of voltage-dependent potassium channels. In this work, we examined the cellular effect of gambierol on cytosolic calcium concentration, membrane potential and sodium and potassium membrane currents in primary cultures of cerebellar granule cells. We found that at concentrations ranging from 0.1 to 30 microM, gambierol-evoked [Ca(2+)]c oscillations that were dependent on the presence of extracellular calcium, irreversible and highly synchronous. Gambierol-evoked [Ca(2+)]c oscillations were completely eliminated by the NMDA receptor antagonist APV and by riluzole and delayed by CNQX. In addition, the K(+) channel blocker 4-aminopyridine (4-AP)-evoked cytosolic calcium oscillations in this neuronal system that were blocked by APV and delayed in the presence of CNQX. Electrophysiological recordings indicated that gambierol caused membrane potential oscillations, decreased inward sodium current amplitude and decreased also outward IA and IK current amplitude. The results presented here point to a common mechanism of action for gambierol and 4-AP and indicate that gambierol-induced oscillations in cerebellar neurons are most likely secondary to a blocking action of the toxin on voltage-dependent potassium channels and hyperpolarization of sodium current activation.

3,4-Diaminopyridine safety in clinical practice: an observational, retrospective cohort study

Fatigue is one of the most common and disabling symptoms of multiple sclerosis (MS) and has a significant, often underestimated, impact on patients' quality of life. Current management is mainly symptomatic. 3,4-diaminopyridine (3,4-DAP) is a voltage-dependent potassium channel blocker that has been used on a named patient basis in Europe for many years to improve motor function and fatigue in patients with MS and other neuromuscular disorders, and it is undergoing the European approval process for Lambert-Eaton myasthenic syndrome (LEMS). The efficacy and safety of 3,4-DAP as symptomatic therapy in MS have not been widely evaluated. This study aimed to assess the safety profile of 3,4-DAP in routine clinical practice in an observational, retrospective study. The study involved 669 patients of the Rennes Multiple Sclerosis Clinic, France, who were treated with 3,4-DAP for the relief of fatigue during the period 1998-2003. Overall, 18.2% of patients presented adverse drug reactions (ADRs) while using moderate doses of 3,4-DAP (20-30 mg daily or up to 80 mg daily for patients with LEMS) for periods of up to 51 months. The majority of ADRs were mild to moderate and transient or reversible at the end of treatment (mean treatment duration = two months) or after dose adjustment. Most did not require discontinuation. The most commonly observed ADRs were paraesthesias. There was one case of epileptic seizure, one of hepatotoxicity and one of heart palpitations thought 'possibly' to be linked to 3,4-DAP. These underline the need for continued monitoring during treatment with 3,4-DAP.

Role of potassium channels in the relaxant effect of levosimendan in guinea pig tracheal preparations

We investigated both the effect of levosimendan and the role of various potassium channels in carbachol-precontracted tracheal preparations samples obtained from guinea pig. The tracheas were cut into 0.5cm wide rings and suspended in a 20ml organ bath. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. Levosimendan or cromakalim produced concentration-dependent relaxation responses in guinea pig tracheal rings precontracted by carbachol. Incubation of guinea pig tracheal rings with the ATP-dependent potassium channel (KATP) blocker glibenclamide for 30 min significantly inhibited the relaxant responses to both levosimendan and cromakalim. The large conductance Ca2+-activated potassium channel (BKCa) blocker iberiotoxin also caused a significant inhibition on relaxant responses to levosimendan. However, incubation of the tracheal rings with the voltage-dependent potassium channel blocker 4-aminopyridine for 10 min did not cause significant alterations on relaxant responses to levosimendan. The present findings suggested that the relaxant effect induced by levosimendan might be partially due to KATP and BKCa in isolated guinea pig tracheal rings.

The role of potassium channels in the vasodilatory effect of caffeine in human internal mammary arteries

There is little information about the direct effect of caffeine in human blood vessels. The purpose of this study was to evaluate the direct vascular effect of caffeine on human internal mammary artery (IMA) and the involvement of potassium channels in this response. Segments of IMA were obtained from 29 patients who underwent coronary artery bypass graft surgery. They were cut into rings, suspended between two wire hooks in organ bath chambers and constricted submaximally with norepinephrine. Caffeine (3.16 × 10 − 9 to 10 − 4 mol/L) was added in a cumulative fashion to rings with or without functional endothelium and concentration response curves were constructed. The response to caffeine was also evaluated after incubation with adenosine 3′,5′-triphosphate (ATP)-dependent potassium channel blocker glibenclamide, voltage-dependent potassium channel blocker 4-aminopyridine and large-conductance calcium-activated potassium channel inhibitor tetraethylammonium. Caffeine produced a potent, concentration-dependent relaxation of IMA. The relaxant responses did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation with different potassium channel inhibitors (glibenclamide, 4-aminopyridine and tetraethylammonium) did not cause significant alterations in the relaxant responses to caffeine. These results suggest that the vasodilatory response to caffeine in human IMA is independent of endothelial function and is not mediated by potassium channels.

The Effect of Hydrogen Peroxide in Human Internal Thoracic Arteries: Role of Potassium Channels, Nitric Oxide and Cyclooxygenase Products

We investigated both the effect and the role(s) of potassium channels, nitric oxide (NO) and cyclooxygenase (COX) products in the effect of hydrogen peroxide (H(2)O(2)) in human internal thoracic artery (ITA) rings. Samples of redundant ITA obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. H(2)O(2) (10(-7)-10(-4) M) produced concentration-dependent relaxation responses in human ITA precontracted by phenylephrine. The relaxant responses to H(2)O(2) did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of human ITA rings with superoxide dismutase (50 U/ml) did not affect the relaxant responses to H(2)O(2), while 1,000 U/ml catalase caused a significant decrease. Incubation of endothelium-intact or endothelium-denuded human ITA rings with voltage-dependent potassium channel blocker 4-aminopyridine (5 mM) significantly inhibited the relaxant responses to H(2)O(2). COX inhibitor indomethacin (10(-5) M) also caused a significant inhibition. Incubation with ATP-dependent potassium channel blocker glibenclamide (10(-6) M) or Ca(2+)-activated potassium channel blocker iberiotoxin (10(-7) M) or NO synthase (NOS) blocker N(omega)-nitro-L: -arginine methyl ester (10(-4) M) did not alter relaxant responses of ITA rings to H(2)O(2). The findings of the present study suggested that H(2)O(2)-induced relaxation responses in human ITA were neither dependant on the endothelium nor blocked by NOS inhibition but they rather seem to depend on the activation of voltage-dependent potassium channels and COX.

Investigation of Relaxant Effects of Propofol on Sheep Sphincter of Oddi

Background/Aims: Intravenous anesthetics are often used for conscious sedation in endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic sphincter of Oddi (SO) manometry. This study was designed to investigate the effects of propofol on sheep SO. Methods: SO rings were mounted in a tissue bath and tested for changes in isometric tension in response to propofol (10^–8–10^–4M) in the presence or absence of L-NAME (3 × 10^–5M), a non-specific inhibitor of nitric oxide (NO) synthase; indomethacin (10^–5M), an inhibitor of cyclooxygenase; glibenclamide (10^–5M), an inhibitor of ATP-sensitive potassium channels; tetraethylammonium (3 × 10^–4M), inhibitors of calcium-activated potassium channels; 4-aminopyridine (10^–3M), a voltage-dependent potassium channel blocker. Furthermore, we investigated the Ca²⁺ antagonist feature of propofol in precontracted SO rings by CaCl₂. Results: Carbachol (10^–9–10^–5M) induced concentration-dependent contraction responses in the SO rings. Propofol (10^–8–10^–4M) produced concentration-dependent relaxation on isolated SO rings precontracted by carbachol (10^–6M). Preincubation of SO rings by L-NAME (3 × 10^–5M), indomethacin (10^–5M), glibenclamide (10^–5M), and 4-aminopyridine (10^–3M) did not produce a significant alteration on propofol-induced relaxation responses (p > 0.05), while preincubation by tetraethylammonium (3 × 10^–4M) significantly decreased the propofol-induced relaxation responses (p < 0.05). Propofol (10^–8–10^–4M) induced concentration-dependently relaxations in precontracted isolated SO rings by CaCl₂. Conclusion: The results suggest that propofol induced concentration-dependent relaxations in precontracted isolated SO rings. These relaxations are independent from NO, cyclooxygenase metabolites, and opened ATP-sensitive and voltage-dependent potassium channels. Opened Ca²⁺-sensitive K⁺ channels and inhibited L-type Ca²⁺ channels existing in smooth muscle by propofol can contribute to these relaxations. Propofol can be beneficial as alternative drugs for obtaining selective relaxation during SO manometry after controlled clinical studies.

The role of potassium channels in the vasodilatory effect of levosimendan in human internal thoracic arteries

We investigated the role of potassium channels in vasodilatory effect of levosimendan in human internal thoracic arteries. Samples of redundant internal thoracic arteries obtained from patients undergoing a coronary artery bypass graft surgery were cut into 3 mm wide rings and suspended in 20 ml organ baths. Isometric tension was continuously measured with an isometric force transducer connected to a computer-based data acquisition system. Levosimendan (10(-8)-10(-5) M) or cromakalim (10(-8)-10(-5) M) produced concentration-dependent relaxation responses in human internal thoracic arteries precontracted by 10(-6) M phenylephrine. The relaxant responses to levosimendan did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of human internal thoracic artery rings with adenosine 3',5'-triphosphate (ATP)-dependent potassium channel blocker glibenclamide (10(-6) M) for 30 min significantly inhibited the relaxant responses to both levosimendan and cromakalim. The Ca2+-activated potassium channel blocker iberiotoxin (10(-7) M) also caused a significant but smaller inhibition on relaxant responses to levosimendan. Incubation of the rings with the voltage-dependent potassium channel blocker 4-aminopyridine (5 mM) for 10 min did not cause significant alterations in relaxant responses to levosimendan. The findings of this study suggested that levosimendan-induced relaxation responses in human internal thoracic arteries were depended on the activation of ATP-dependent and Ca2+-activated potassium channels.

The Role of Potassium Channels in Relaxant Effect of Levosimendan in Rat Small Mesenteric Arteries

We investigated both the effect of levosimendan and the role of various potassium channels in KCl-precontracted rat small mesenteric arteries. Levosimendan (10(-6)-10(-3) M) or cromakalim (CRO, 10(-7)-10(-4) M) produced concentration-dependent relaxation responses in small mesenteric arteries precontracted by 30 mM KCl. The relaxant responses to levosimendan in KCl-precontracted arteries did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of rat small mesenteric arterial segments with ATP-dependent potassium channel (KATP) blocker glibenclamide (GLI, 10(-6) M) for 30 min significantly inhibited the relaxant responses to both levosimendan and CRO. Neither the Ca(2+)-activated potassium channel (KCa) blocker iberiotoxin (10(-7) M) nor the voltage-dependent potassium channel (KV) blocker 4-aminopyridine (5 mM) incubation for 30 min caused significant alterations in relaxant responses to levosimendan in KCl-precontracted small mesenteric arteries. These findings suggested that levosimendan-induced relaxation responses in isolated rat small mesenteric arteries were neither depended on endothelium nor inhibited by the blockers of KV or KCa but, they rather seem to depend on the activation of KATP.

Perivascular adipose tissue modulates vascular function in the human internal thoracic artery

Recent studies have shown that perivascular adipose tissue from the rat aorta secretes a substance that can dilate the aorta. The purpose of the present study was to examine whether this vasodilator is also present in human internal thoracic arteries. Vascular function of human internal thoracic arteries with and without perivascular adipose tissue was assessed with wire myography, and morphology was examined with light microscopy. The presence of perivascular adipose tissue attenuated the maximal contraction to U 46619 and the contraction to phenylephrine (1 micromol/L) by 37% and 24%, respectively. Transfer of the solution incubated with a perivascular adipose tissue-intact vessel (donor) to a vessel without perivascular adipose tissue (recipient) induced a significant relaxation (36%) in the recipient artery precontracted with phenylephrine. Transfer of incubation solution with perivascular adipose tissue alone also induced a relaxation response in the recipient vessel (37%). The relaxation of the recipient artery induced by the transfer of incubation solution from the donor (artery with intact perivascular adipose tissue or perivascular adipose tissue alone) was absent in vessels precontracted by KCl (60 mmol/L) and was prevented by calcium-dependent potassium channel blockers (tetraethylammonium chloride, 1 mmol/L; iberiotoxin, 100 nmol/L), but not by the voltage-dependent potassium channel blocker 4-aminopyridine (1 mmol/L) and the adenosine triphosphate-dependent potassium channel blocker glibenclamide (10 micromol/L). Perivascular adipose tissue in human internal thoracic arteries releases a transferable relaxation factor that acts through the activation of calcium-dependent potassium channels. Because perivascular adipose tissue is often removed in coronary artery bypass grafting, retaining perivascular adipose tissue might be helpful in reducing the occurrence of vasospasm of the graft vessels.

D-Tubocurarine-Sensitive Component of Calcium-Dependent Potassium Current in Guinea Pig Taenia Coli Myocytes

Using a patch-clamp technique in the whole-cell configuration, we studied transmembrane ion currents in isolated single smooth muscle cells of the guinea pig taenia coli. A depolarizing step shift of the membrane potential from −50 mV was accompanied by the appearance of an outward current. Application of d-tubocurarine (d-TK) or a nonselective blocker of voltage-dependent potassium channels, tetraethylammonium (TEA), led to a decrease in the outward current. Application of d-TK against the background of the action of TEA additionally decreased the outward current. Analysis of the current-voltage (I–V) relationships of the d-TK-sensitive current showed that this current is practically voltage-independent. At the same time, an inflection of the I–V curve of the potassium current within the segment of maximum activation of the voltage-dependent potassium current is indicative of the sensitivity of this current to the intracellular Ca2+ concentration. Therefore, the calcium-activated potassium current through small-conductance calcium-dependent potassium channels includes a d-TK-sensitive voltage-independent component. Using depolarizing shifts of the membrane potential, we observed high- and low-amplitude spontaneous outward currents (SOCs) in many studied cells, i.e., the effect of an increase in the conductance of calcium-dependent potassium channels as a result of periodic release of Ca2+ from the intracellular stores. Application of d-TK led to a decrease in the frequency of low-amplitude SOCs and exerted nearly no influence on the high-amplitude SOCs under study.