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At least 127 records · Page 7Linked to original sources
PubMed1998

Epoxyeicosatrienoic acids, potassium channel blockers and endothelium-dependent hyperpolarization in the guinea-pig carotid artery.

1. Using intracellular microelectrodes, we investigated the effects of 17-octadecynoic acid (17-ODYA) on the endothelium-dependent hyperpolarization induced by acetylcholine in the guinea-pig isolated internal carotid artery with endothelium. 2. In the presence of Nomega-nitro-L-arginine (L-NOARG, 100 microM) and indomethacin (5 microM) to inhibit nitric oxide synthase and cyclo-oxygenase, acetylcholine (1 microM) evoked an endothelium-dependent hyperpolarization which averaged -16.4 mV starting from a resting membrane potential of -56.8 mV. There was a negative correlation between the amplitude of the hyperpolarization and the absolute values of the resting membrane potential. 3. The acetylcholine-induced endothelium-dependent hyperpolarization was not altered by charybdotoxin (0.1 microM) or iberiotoxin (30 nM). It was partially but significantly reduced by apamin (0.5 microM) to -12.8+/-1.2 mV (n=10) or the combination of apamin plus iberiotoxin (-14.3+/-3.4mV, n=4). However, the combination of charybdotoxin and apamin abolished the hyperpolarization and under these conditions, acetylcholine evoked a depolarization (+ 7.1+/-3.7 mV, n = 8). 4. 17-ODYA (10 microM) produced a significant hyperpolarization of the resting membrane potential which averaged -59.6 mV and a partial but significant inhibition of the acetylcholine-induced endothelium-dependent hyperpolarization (-10.9 mV). 5. Apamin did not modify the effects of 17-ODYA but in the presence of charybdotoxin or iberiotoxin, 17-ODYA no longer influenced the resting membrane potential or the acetylcholine-induced hyperpolarization. 6. When compared to solvent (ethanol, 1% v/v), epoxyeicosatrienoic acids (EpETrEs) (5,6-, 8,9-, 11,12- and 14,15-EpETrE, 3 microM) did not affect the cell membrane potential and did not relax the guinea-pig isolated internal carotid artery. 7. These results indicate that, in the guinea-pig internal carotid artery, the involvement of metabolites of arachidonic acid through the cytochrome P450 pathway in endothelium-dependent hyperpolarization is unlikely. Furthermore, the hyperpolarization mediated by the endothelium-derived hyperpolarizing factor (EDHF) is probably not due to the opening of BK(Ca) channels.

8,11,14-Eicosatrienoic Acid↗
PubMed2006

Structure-based secondary structure-independent approach to design protein ligands: Application to the design of Kv1.2 potassium channel blockers.

We have developed a structure-based approach to the design of protein ligands. This approach is based on the transfer of a functional binding motif of amino acids, often referred as to the "hot spot", on a host protein able to reproduce the functional topology of these residues. The scaffolds were identified by a systematic in silico search in the Protein Data Bank for proteins possessing a group of residues in a topology similar to that adopted by the functional motif in a reference ligand of known 3D structure. In contrast to previously reported studies, this search is independent of the particular secondary structure supporting the functional motif. To take into account the global properties of the host protein, two additional criteria were taken into account in the selection process: (1) Only those scaffolds sterically compatible with the positioning of the functional motif as observed in a reference complex model were retained. (2) Host proteins displaying electrostatic potentials, in the region of the transferred functional motif, similar to that of the reference ligand were selected. This approach was applied to the development of protein ligands of the Kv1.2 channel using BgK, a small protein isolated from the sea anemone Bunodosoma granulifera, as the reference ligand. Four proteins obtained by this approach were produced for experimental evaluation. The X-ray structure of one of these proteins was determined to check for similarity of the transferred functional motif with the structure it adopts in the reference ligand. Three of these protein ligands bind the Kv1.2 channel with inhibition constants of 0.5, 1.5, and 1.6 microM. Several mutants of these designed protein ligands gave binding results consistent with the presumed binding mode. These results show that protein ligands can be designed by transferring a binding motif on a protein host selected to reproduce the functional topology of this motif, irrespective to the secondary structure supporting the functional motif, if the host protein possesses steric and electrostatic properties compatible with the binding to the target. This result opens the way to the design of protein ligands by taking advantage of the considerable structural repertoire of the Protein Data Bank.

Amino Acid Sequence↗
PubMed1988

Bupivacaine is an effective potassium channel blocker in heart.

The local anesthetic agent bupivacaine increases action potential duration in isolated frog atrial myocytes, and blocks two potassium conductances, IK and IK1. The effective concentrations, particularly for IK, are similar to those which depress the sodium conductance. Potassium channel block may thus contribute to bupivacaine's reported cardiotoxicity.

Action Potentials↗
PubMed2000

Electropharmacological characterization of cardiac repolarization in German shepherd dogs with an inherited syndrome of sudden death: abnormal response to potassium channel blockers.

OBJECTIVES: This study sought to determine whether abnormal ventricular repolarization is implicated in cardiac arrhythmias of German shepherd dogs with inherited sudden death. BACKGROUND: Moïse et al. (9) have identified German shepherd dogs that display pause-dependent lethal ventricular arrhythmias. METHODS: Ventricular repolarization was studied both in vivo using electrocardiogram recordings on conscious dogs and in vitro with a standard microelectrode technique performed on endomyocardial biopsies and Purkinje fibers. Pharmacological manipulation was used to evaluate the role of potassium channels. RESULTS: In control conditions, electrocardiogram parameters were similar in both groups of dogs, except for the PR interval (18% longer in affected dogs, p < 0.05). Injection of d,l-sotalol (2 mg/kg) prolonged QT interval more in affected dogs (+14%, n = 9) than it did in unaffected dogs (+6%, n = 6, p < 0.05) and increased the severity of arrhythmias in affected dogs. In vitro, in control conditions, action potential duration (APD90) of endomyocardial biopsies and Purkinje fibers were significantly longer in affected dogs (respectively 209 +/- 3 ms, n = 30 and 352 +/- 15 ms, n = 17) than they were in unaffected dogs (197 +/- 4 ms, n = 25 and 300 +/- 9 ms, n = 30) at a pacing cycle length (PCL) of 1,000 ms. This difference increased with PCL. The kinetics of adaptation of APD90 to a change in PCL was faster in affected dogs. D,l-sotalol (10(-5) and 10(-4)M) increased APD90 in both groups of dogs, but this increase was greater in affected dogs, with the occurrence of triggered activity on Purkinje fibers. E-4031 (10(-7) and 10(-6) M), an I(Kr)-blocker, increased APD90 similarly in both groups of dogs. Chromanol 293B (10(-6) and 10(-5)M), an I(Ks)-blocker, increased significantly APD90 in unaffected dogs but had no effect in affected dogs. CONCLUSIONS: These results support the hypothesis of an abnormal cardiac repolarization in affected dogs. The effects of 293B suggest that I(Ks) may be involved in this anomaly.

Animals↗
PubMed1989

Effect of some potassium channel blockers on contractile responses of the rabbit aorta.

Contractile responses of rabbit aortic rings to KCl or angiotensin II (AII) were investigated in the presence of five compounds known to block K+ channels. Tetraethylammonium (3 and 10 mM), 3,4-diaminopyridine (0.3 and 1 mM), and a charybdotoxin-like toxin from the venom of the scorpion Leiurus quinquestriatus hebraeus (3-30 ng ml-1), augmented contractions due to low but not high KCl concentrations and increased the maximum tissue response to AII. This latter augmentation could be reduced (but not fully inhibited) by the calcium entry blocker PN 200-100 (100 nM), implicating an influx of extracellular calcium in the response. 3,4-Diaminopyridine (1 mM) and the scorpion toxin additionally increased the resting tension of the aortic rings, an effect not observed with tetraethylammonium at concentrations up to 10 mM. Apamin and toxin I (both 1 microM) failed to modify KCl or AII contractions of the aorta. In all cases, aortic rings denuded of endothelium gave essentially the same results as rings having an intact endothelium. These results are discussed in relation to the possible types of K+ channels involved in modulating the tone of this blood vessel during hormonal stimulation.

4-Aminopyridine↗
PubMed1996

[The new potassium channel blocker tedisamil and its hemodynamic, anti-ischemic and neurohumoral effect in patients with coronary heart disease].

Thirty-two patients with angiographically proven coronary artery disease and reproducible ST-segment depression in the exercise ECG took part in this open dose-finding study on the hemodynamic and anti-ischemic effects of tedisamil, using right heart catheterization and bicycle exercise testing. Tedisamil--a bispidine derivative--is a new potassium channel blocking agent with negative chronotropic (i.e., direct effects on sinus node automaticity) and class III antiarrhythmic properties. Four groups of 8 patients each received rising doses of 0.1, 0.2, 0.3, and 0.4 mg/kg BW tedisamil intravenously. Being well tolerated, tedisamil was found to be dose-linear with the dose of 0.3 mg/kg BW having the most favorable anti-ischemic effects accompanied by a significant decrease in heart rate at rest (-13%, p < 0.001) and maximum exercise (-9%, p < 0.05). There was a consecutive fall of CO (by 10%, p < 0.05), while stroke volume remained unaltered. Despite singular significant changes, PCWPm and RV-EF, as indirect parameters of ventricular function, showed different responses without a clear tendency. PAPm increased slightly in accordance with peripheral and pulmonary vascular resistance, being significant at 3.3 mm Hg (p < 0.05) only at the dose of 0.4 mg/kg BW. Mean arterial pressure demonstrated a slight increase at rest (9% at 0.4 mg/kg BW; p < 0.05). Plasma catecholamine levels fell in a dose-dependent way by a maximum of 115-150 pg/ml (p < 0.01) on treatment with 0.4 mg/kg BW. QTc was found significantly prolonged by 16% (p < 0.001) on 0.4 mg/kg BW. During treatment with 0.3 mg/kg BW, tedisamil produced a dose-dependent reduction of ST segment depression at a maximum of 42% (p < 0.001) as well as a decrease in myocardial oxygen consumption, pressure rate product, and plasma lactate concentrations. In conclusion, tedisamil lowered heart rate and showed favorable hemodynamic, anti-ischemic, and neurohumoral effects in patients with coronary artery disease.

Aged↗
PubMed1984

Actions of potassium channel blockers on guinea-pig lateral olfactory tract axons.

Population action potentials were recorded from the guinea-pig isolated lateral olfactory tract. At 30 degrees C, the conduction velocity of the fibres was about 4 m/s and the absolute refractory period was less than or equal to 1.5 ms. The population spike was unaffected by removal of calcium ions from the superfusate but was abolished in tetrodotoxin. Tetraethylammonium ions (10 mmol/l) had no effect on the population spike, however the following potassium channel blocking drugs increased the duration in a concentration-dependent manner (in order of decreasing potency): 3,4-diaminopyridine, 4-aminopyridine, 3-aminopyridine, sparteine, cesium ions and barium ions. In addition to a prolongation, these substances also reduced the amplitude of the conducted spike. It is concluded that the rising phase of the spike is generated by a voltage-dependent increase in sodium conductance and that an increase in potassium conductance contributes to the falling phase. The potassium channels are potently blocked by aminopyridine like drugs.

4-Aminopyridine↗
PubMed1990

Effects of potassium channel blockers on baclofen-induced suppression of paroxysmal discharges in rat neo-cortical slices.

Baclofen reduced the frequency and aborted the bursts of spontaneous paroxysmal discharges in rat neocortical slices maintained in magnesium-free medium. This action was prevented by pretreatment with barium or caesium, which each increased the ictaform burst frequency, amplitude and duration. 4-Amino-pyridine also increased the burst frequency but reduced the amplitude and did not completely prevent the action of baclofen. Evidently baclofen suppresses such discharges by opening potassium channels normally involved in limiting the burst activity.

4-Aminopyridine↗
PubMed1991

Potassium channel blockers potentiate impulse inhibition by local anesthetics.

The ability of local anesthetics to reduce the amplitude of compound action potentials (CAP) of frog sciatic nerve was examined in the absence and presence of agents that selectively block K+ channels. In the presence of lidocaine concentrations that inhibit the CAP by about 20% at low frequencies of stimulation (1 per min, "tonic inhibition"), the addition of the K(+)-channel blocker tetraethylammonium ion (TEA, 12 mM) increased this inhibition by another 15%. Furthermore, the use-dependent inhibition induced by lidocaine at higher stimulation frequencies (5-20 Hz, "phasic inhibition") was markedly enhanced by TEA: at 20 Hz it increased from 35% with lidocaine alone to 63% with lidocaine plus TEA. A comparable potentiation was rendered by 3,4-diaminopyridine (1 mM), a different K(+)-channel blocker. Similarly, phasic inhibition by bupivacaine also was enhanced by TEA. The K(+)-channel blockers alone slightly depolarized the resting membrane, broadened and elevated the CAP, produced no phasic inhibition, and, during repetitive stimulation, resulted in a less negative steady-state repolarization potential than at rest. Both the broadening of CAP and the depolarizing actions of K(+)-channel blockers increased the presence of open and inactivated states of the neuronal Na+ channels, and thereby enhanced the binding of local anesthetic. The inhibitory actions of saxitoxin, a Na(+)-channel blocker that binds equally well to all channel states, were not potentiated by TEA.

4-Aminopyridine↗