Objective: To determine the electrophysiological effects and related mechanisms of late sodium current inhibitors on hearts with short QT intervals. Methods: The electrophysiological study was performed on isolated Langendorff perfused rabbit hearts. A total of 80 New Zealand White rabbits were used and 34 hearts without drug treatment were defined as control group A, these hearts were then treated with I_KATP opener pinacidil, defined as pinacidil group A. Then, 27 hearts from pinacidil group A were selected to receive combined perfusion with sodium channel inhibitors or quinidine, a traditional drug used to treat short QT syndrome, including ranolazine combined group (n=9), mexiletine combined group (n=9), and quinidine combined group (n=9). Nineteen out of the remaining 46 New Zealand rabbits were selected as control group B (no drug treatments, n=19), and then treated with pinacidil, defined as pinacidil group B (n=19). The remaining 27 rabbits were treated with sodium inhibitors or quinidine alone, including ranolazine alone group (n=9), mexiletine alone group (n=9), and quinidine alone group (n=9). Electrocardiogram (ECG) physiological parameters of control group A and pinacidil group A were collected. In control group B and pinacidil group B, programmed electrical stimulation was used to induce ventricular arrhythmias and ECG was collected. ECG physiological parameters and ventricular arrhythmia status of various groups were analyzed. The concentrations of pinacidil, ranolazine, mexiletine and quinidine used in this study were 30, 10, 30 and 1 μmol/L, respectively. Results: Compared with control group A, the QT interval, 90% of the repolarization in epicardial and endocardial monophasic action potential duration (MAPD₉₀-Epi, MAPD₉₀-Endo) was shortened, the transmural dispersion of repolarization (TDR) was increased, and the effective refractor period (ERP) and post-repolarization refractoriness (PRR) were reduced in pinacidil group A (all P<0.05). Compared with the pinacidil group A, MAPD₉₀-Epi, MAPD₉₀-Endo, QT interval changes were reversed in quinidine combined group and mexiletine combined group (all P<0.05), but not in ranolazine combined group. All these three drugs reversed the pinacidil-induced increases of TDR and the decreases of ERP and PRR. The induced ventricular arrhythmia rate was 0 in control group B, and increased to 10/19 (χ²=13.6, P<0.05) in pinacidil group B during programmed electrical stimulation. Compared with the pinacidil group B, incidences of ventricular arrhythmia decreased to 11% (1/9), 11% (1/9) and 0 (0/9) (χ²=4.5, 4.5, 7.4, P<0.05) respectively in ranolazine group, mexiletine group and quinidine group. Conclusions: Inhibition of late sodium current does not increase but even decreases the risk of malignant arrhythmia in hearts with a shortened QT interval. The antiarrhythmic mechanism might be associated with the reversal of the increase of TDR and the decrease of refractoriness (including both ERP and PRR) of hearts with shortened QT interval.
Rabbits ; Animals ; Quinidine/therapeutic use* ; Mexiletine/therapeutic use* ; Pinacidil/therapeutic use* ; Sodium ; Ranolazine/therapeutic use* ; Electrophysiologic Techniques, Cardiac ; Arrhythmias, Cardiac/drug therapy*

Lubiprostone is a chloride (Cl-) channel activator derived from prostaglandin E1 and used for managing constipation. In addition, lubiprostone affects the activity of gastrointestinal smooth muscles. Interstitial cells of Cajal (ICCs) are pacemaker cells that generate slow-wave activity in smooth muscles. We studied the effects of lubiprostone on the pacemaker potentials of colonic ICCs. We used the whole-cell patch-clamp technique to determine the pacemaker activity in cultured colonic ICCs obtained from mice. Lubiprostone hyperpolarized the membrane and inhibited the generation of pacemaker potentials. Prostanoid EP1, EP2, EP3, and EP4 antagonists (SC-19220, PF-04418948, 6-methoxypyridine-2-boronc acid N-phenyldiethanolamine ester, and GW627368, respectively) did not block the response to lubiprostone. L-NG-nitroarginine methyl ester (L-NAME, an inhibitor of nitric oxide synthase) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) did not block the response to lubiprostone. In addition, tetraethylammonium (TEA, a voltage-dependent potassium [K+] channel blocker) and apamin (a calcium [Ca2+]-dependent K+ channel blocker) did not block the response to lubiprostone. However, glibenclamide (an ATP-sensitive K+ channel blocker) blocked the response to lubiprostone. Similar to lubiprostone, pinacidil (an opener of ATP-sensitive K+ channel) hyperpolarized the membrane and inhibited the generation of pacemaker potentials, and these effects were inhibited by glibenclamide. These results suggest that lubiprostone can modulate the pacemaker potentials of colonic ICCs via activation of ATP-sensitive K+ channel through a prostanoid EP receptor-independent mechanism.
Alprostadil ; Animals ; Apamin ; Calcium ; Colon* ; Constipation ; Glyburide ; Interstitial Cells of Cajal* ; Membranes ; Mice* ; Muscle, Smooth ; Nitric Oxide ; Patch-Clamp Techniques ; Pinacidil ; Potassium ; Tetraethylammonium ; Lubiprostone

BACKGROUNDMany studies have indicated that hyperpolarizing cardioplegia is responsible for myocardial preservation and researchers have suggested that the adenosine triphosphate-sensitive potassium channels (K(ATP)) were the end effectors of cardio-protection. But whether mitochondrial K(ATP) plays an important role in hyperpolarizing cardioplegia is not apparent. The present study investigated the effect of hyperpolarizing cardioplegia containing pinacidil (a nonselective K(ATP) opener) on ischemia/reperfusion injury in rat hearts, especially the role of mitochondrial K(ATP) in pinacidil hyperpolarizing cardioplegia.

METHODSSprague-Dawley rat hearts were Langendorff-perfused for 20 minutes with Krebs-Henseleit buffer at 37°C before equilibration. Cardiac arrest was then induced in different treatments: there was no arrest and ischemia in the normal group, the control group were arrested by clamping the aorta, depolarizing caidioplegia (St. Thomas solution containing 16 mmol/L KCl) and hyperpolarizing cardioplegia groups used St. Thomas solution containing 0.05 mmol/L pinacidil and 5 mmol/L KCl to induce cardiac arrest in group hyperkalemic and group pinacidil, in group hyperkalemic + 5-hydroxydecanote (5HD) and Pinacidil + 5HD, 5HD (0.1 mmol/L) was added to the above two solutions to block mitochondria K(ATP) channels. Global ischemia was then administrated for 40 minutes at 37°C, followed by 30 minutes of reperfusion. At the end of equilibration and reperfusion, hemodynamics, ultrastructure, and mitochondrial function were measured.

RESULTSIn the control group, ischemia/reperfusion decreased the left ventricular developed pressure, heart rate, coronary flow, mitochondrial membrane potential, impaired mitochondrial respiratory function, increased reactive oxygen species and left ventricular end diastolic pressure. Damage to myocardial ultrastructure was also evident. Both depolarized arrest and especially hyperpolarized cardioplegia significantly reduced these lesions. 5HD partially blocked the beneficial effects of pinacidil cardioplegia but showing no effects on hyperkalemic arrest.

CONCLUSIONSPinacidil cardioplegia provides better cardioprotection with preservation of hemodynamics, ultrastructure, and mitochondrial function than traditional cardioplegia. The mitochondria K(ATP) channels may play an important role in the protection mechanism.

Animals ; Hemodynamics ; drug effects ; Membrane Potential, Mitochondrial ; drug effects ; Microscopy, Electron, Transmission ; Myocardial Reperfusion Injury ; drug therapy ; metabolism ; Myocardium ; metabolism ; ultrastructure ; Pinacidil ; therapeutic use ; Potassium Channels ; metabolism ; Rats ; Rats, Sprague-Dawley ; Reactive Oxygen Species ; metabolism

PURPOSE: Evidence has emerged that oxygen-derived free radicals may induce vascular relaxations via ATP-sensitive K+ (K(ATP)) channels and the level of free radicals is increased in animal models of hypertension. The present study was conducted to determine whether relaxations to an K(ATP) channel opener, pinacidil, are increased in the aorta from two-kidney, one clip (2K1C) hypertensive rats and whether free radial scavengers reduce these relaxations. METHODS: 2K1C hypertension was induced by clipping the left renal artery and age-matched control rats received a sham treatment. Rings of aortae without endothelium were suspended for isometric force recording. RESULTS: Relaxations to pinacidil (10(-8) to 10(-5) M), which are abolished by glibenclamide (10(-5) M), were augmented in the aorta from 2K1C rats, compared to those from control rats. In the aorta from 2K1C rats, catalase (1,200 U/mL), but neither superoxide dismutase (150 U/mL) nor deferoxamine (10(-4) M), reduced relaxations to pinacidil, whereas in the aorta from control rats, the free radical scavengers did not affect these relaxations. CONCLUSION: These results suggest that in 2K1C hypertension, vasorelaxation to an KATP channel opener is augmented and that hydrogen peroxide in smooth muscle cells may partly contribute to these relaxations.
Animals ; Aorta ; Catalase ; Deferoxamine ; Endothelium ; Free Radical Scavengers ; Free Radicals ; Glyburide ; Hydrogen Peroxide ; Hypertension ; Hypertension, Renal ; Models, Animal ; Myocytes, Smooth Muscle ; Pinacidil ; Placebos ; Rats ; Relaxation ; Renal Artery ; Salicylamides ; Superoxide Dismutase ; Vasodilation

PURPOSE: This study is to assess the pharmacologic effects of ethanol and its metabolite, acetaldehyde on potassium channels of the corpus cavernosal smooth muscle of the rabbit. MATERIALS AND METHODS: Cavernosal strips from New Zealand white rabbits were harvested and pharmacophysiologic organ bath studies were executed. In equilibrium state after incubation, zaprinast (PDE5 inhibitor) induced relaxations were monitored in strips precontracted with phenylephrine (PE, 10(-4)M). The inhibitory effects of ethanol and acetaldehyde (2, 20, 40, 80 mmol) on zaprinast-induced relaxations were recorded. Pinacidil (K(ATP) channel opener) and phloretin (BK channel opener) were tested to reverse the inhibitory effects of ethanol and acetaldehyde on zaprinast-induced relaxations. RESULTS: Both ethanol and acetaldehyde inhibited the zaprinast-induced relaxations in a dosedependent manner (p<0.05). Both pinacidil and phloretin abolished the inhibition by both ethanol and acetaldehyde (p<0.05). Ethanol and acetaldehyde inhibits cavernosal relaxation, possibly through BK channels and K(ATP) channels. CONCLUSIONS: These results suggest that ethanol and its metabolite may affect the corpus cavernosal smooth muscle directly and lead to consequent erectile dysfunction. Furthermolecular and electrophysiological studies will help reveal the underlying mechanisms to which this process occurs.
Acetaldehyde ; Baths ; Erectile Dysfunction ; Ethanol ; Large-Conductance Calcium-Activated Potassium Channels ; Male ; Muscle, Smooth ; Penis ; Phenylephrine ; Phloretin ; Pinacidil ; Potassium Channels ; Purinones ; Rabbits ; Relaxation

NO released by myenteric neurons controls the off contraction induced by electrical field stimulation (EFS) in distal esophageal smooth muscle, but in the presence of nitric oxide synthase (NOS) inhibitor, L-NAME, contraction by EFS occurs at the same time. The authors investigated the intracellular signaling pathways related with G protein and ionic channel EFS-induced contraction using cat esophageal muscles. EFS-induced contractions were significantly suppressed by tetrodotoxin (1 micrometer) and atropine (1 micrometer). Furthermore, nimodipine inhibited both on and off contractions by EFS in a concentration dependent meaner. The characteristics of 'on' and 'off' contraction and the effects of G-proteins, phospholipase, and K+ channel on EFS-induced contraction in smooth muscle were also investigated. Pertussis toxin (PTX, a Gi inactivator) attenuated both EFS-induced contractions. Cholera toxin (CTX, Gs inactivator) also decreased the amplitudes of EFS-induced off and on contractions. However, phospholipase inhibitors did not affect these contractions. Pinacidil (a K+ channel opener) decreased these contractions, and tetraethylammonium (TEA, K+ Ca channel blocker) increased them. These results suggest that EFS-induced on and off contractions can be mediated by the activations Gi or Gs proteins, and that L-type Ca2+ channel may be activated by G-protein alpha subunits. Furthermore, K+ Ca-channel involve in the depolarization of esophageal smooth muscle. Further studies are required to characterize the physiological regulation of Ca2+ channel and to investigate the effects of other K+ channels on EFS-induced on and off contractions.
Animals ; Atropine ; Cats ; Cholera Toxin ; Contracts ; GTP-Binding Protein alpha Subunits ; GTP-Binding Proteins ; Ion Channels ; Muscle, Smooth ; Muscles ; Neurons ; NG-Nitroarginine Methyl Ester ; Nimodipine ; Nitric Oxide Synthase ; Pertussis Toxin ; Phospholipases ; Pinacidil ; Proteins ; Tetraethylammonium ; Tetrodotoxin

OBJECTIVETo investigate effect of pinacidil, an ATP sensitive potassium channel (K(ATP)) opener, on the neuronal apoptosis and its signaling transduction mechanism following focal cerebral ischemia-reperfusion in rats.

METHODSOne hundred male Wistar rats were randomly divided into four groups: A, sham-operated group; B, ischemia-reperfusion group; C, K(ATP) opener treatment group; and D, K(ATP) opener and blocker treatment group. The middle cerebral artery occlusion (MCAO) model was established by using the intraluminal suture occlusion method, neuronal apoptosis was determined by TUNEL staining, and expressions of caspase-8, caspase-9 and caspase-3 mRNA were detected by in situ hybridization.

RESULTS(1) The numbers of apoptotic neurons at 12 h, 24 h, 48 h, and 72 h were significantly less in group C than in groups B and D (P< 0.01 or P< 0.05); and there was no difference between groups B and D at all time points (P> 0.05). (2) The expressions of caspase-3 mRNA and caspase-8 mRNA at all times and the expressions of caspase-9 mRNA at 12 h, 24 h, 48 h, 72 h were significantly lower in group C than in groups B and D (P< 0.01 or P< 0.05); and there were no differences between groups B and D at all time points (P> 0.05).

CONCLUSIONSK(ATP) opener can significantly decrease the neuronal apoptosis and the expressions of caspase-3, caspase-8 and caspase-9 mRNAs following cerebral ischemia-reperfusion. The neuronal apoptosis may be decreased by the inhibition of both mitochondrial and death-receptor signal pathways.

Animals ; Antihypertensive Agents ; therapeutic use ; Apoptosis ; drug effects ; Brain Ischemia ; drug therapy ; Caspases ; metabolism ; Gene Expression Regulation ; drug effects ; In Situ Nick-End Labeling ; Male ; Neurons ; drug effects ; Pinacidil ; therapeutic use ; RNA, Messenger ; metabolism ; Rats ; Rats, Wistar ; Reperfusion Injury ; drug therapy ; Time Factors

To investigate whether hydrogen peroxide (H2O2) affects intestinal motility, pacemaker currents and membrane potential were recorded in cultured interstitial cells of Cajal (ICC) from murine small intestine by using a whole-cell patch clamp. In whole cell patch technique at 30 degress C, ICC generated spontaneous pacemaker potential under current clamp mode (I=0) and inward currents (pacemaker currents) under voltage clamp mode at a holding potential of -70 mV. When ICC were treated with H2O2 in ICC, H2O2 hyperpolarized the membrane potential under currents clamp mode and decreased both the frequency and amplitude of pacemaker currents and increased the resting currents in outward direction under voltage clamp mode. Also, H2O2 inhibited the pacemaker currents in a dose-dependent manner. Because the properties of H2O2 action on pacemaker currents were same as the effects of pinacidil (ATP-sensitive K+ channels opener), we tested the effects of glibenclamide (ATP-sensitive K+ channels blocker) on H2O2 action in ICC, and found that the effects of H2O2 on pacemaker currents were blocked by co- or pre-treatment of glibenclamide. These results suggest that H2O2 inhibits pacemaker currents of ICC by activating ATP-sensitive K(+) channels.
Gastrointestinal Motility ; Glyburide ; Hydrogen Peroxide* ; Hydrogen* ; Interstitial Cells of Cajal* ; Intestine, Small ; Membrane Potentials ; Pinacidil

This study was aimed to elucidate the effects of K(ATP) activation during IPC on the PKC-epsilon, NF-kappaB and AP-1 in ischemia-reperfused rat hearts. SD male rats weighting from 300 to 350 g were split into 9 groups, such as sham control (S), IPC, 3 cycles of 5 min ischemia and 5 min reperfusion, continuous preconditioning (CP), 8 cycles of 5 min ischemia and 5 min reperfusion, K(ATP) opening (KO) with pinacidil (1.0 mg/kg), K(ATP) blocking with glibenclamide (1.0 mg/kg) injection, ischemia (IS), 30 min ischemia, IPC followed by IS, 8) K(ATP) blocking and IPC followed by IS (KB+IPC+IS), IS and K(ATP) opening (KO+IS). Heart were subjected to ligation of left descending coronary artery and reperfusion in groups of IPC, CP, IS with or without IPC. Immunohistochemistry and Western blotting for PKC-epsilon, NF-kappaB and AP-1 were performed at 3, 6, 24 hours after reperfusion or treatment. Immunoreactivities against PKC-epsilon antibody were observed stronger in the groups of IPC, KO, IPC+IS and KO+IS than groups of KB, IS and KB+IPC+IS. NF-kappaB activation and translocation were only observed in the groups of including 30 min ischemia and reperfusion. AP-1 activation and translocation were opposite to the results of PKC-epsilon activation. In the group of CP, KB, IS and KB+IPC+IS, reactivities of AP-1 antibody were stronger than IPC+IS, KO+IS, and weaker in the groups of S, IPC and KO. These results suggest that K(ATP) opening with IPC or pharmacological methods may direct effect on the PKC-epsilon activation and that K(ATP) blocking has effect on the AP-1 activation and translocation in the heart of ischemiareperfused of rats.
Animals ; Blotting, Western ; Coronary Vessels ; Glyburide ; Heart* ; Humans ; Immunohistochemistry ; Ischemia ; Ischemic Preconditioning* ; Ligation ; Male ; NF-kappa B* ; Pinacidil ; Rats* ; Reperfusion ; Transcription Factor AP-1*

OBJECTIVEOn the basis that pinacidil can produce an "all or none" repolarization in right ventricular wall of canine, to observe the effects of quinidine on the marked transmural dispersion of repolarization. Recent studies have shown that ventricular myocardium is composed of at least 3 electrophysiological distinct cell types: epicardial, endocardial, and midcardial cells. Differences in the response of the 3 cell types to pharmacologic agents and/or pathophysiological states often result in amplification of intrinsic electrical heterogeneities, thus providing a substrate as well as a trigger for the development of arrhythmias. The study was designed to observe the right ventricular transmural heterogeneity in vitro canine heart tissue preparation level.

METHODSThe strips were isolated from the anterior wall of the right ventricular of canine. The preparations perfused with oxygenated (95%O(2)/5%CO(2)) Tyrode's solution. The tissues were stimulated at basic cycle lengths of 1000 ms. Standard microelectrode techniques were used. Transmembrane action potentials were recorded from epicardial, midcardial and endocardial cells respectively from right ventricular free wall of canine on different conditions [perusing with Tyrode's solution (Control), pinacidil (2.5 micromol/L), and quinidine (5 micromol/L) in turn].

RESULTSCompared with that of endocardial cells, the action potentials of canine ventricular epicardial and midcardial cells had more obvious spike and dome morphology. Pinacidil (2.5 micromol/L) caused a loss of the dome of transmembrane action potentials and a marked abbreviation of the action potential duration (APD) in right ventricular epicardial and midcardial cells, especially in epicardial cells, but not in endocardial cells (n = 10). With pinacidil (2.5 micromol/L), in epicardial cells, phase 2 amplitude of action potentials decreased from (117.7 +/- 9.3) mV to (71.3 +/- 6.4) mV (P < 0.01), and 90% of the APD(90) decreased from (198.2 +/- 20.8) ms to (103.9 +/- 13.5) ms (P < 0.01). The transmural dispersion of action potential duration increased from (48.5 +/- 9.2) ms to (128.7 +/- 13.5) ms (P < 0.01). Quinidine (5 micromol/L) effectively prolonged the APD abbreviated by pinacidil, restored or partly restored the dome of transmembrane action potentials of epicardial and midcardial cells but not of endocardial cells (n = 10). In epicardial cells phase 2 amplitude increased from (71.3 +/- 6.4) mV to (106.6 +/- 7.7) mV (P < 0.01), and 90% of the APD(90) increased from (103.9 +/- 13.5) ms to (185.9 +/- 15.7) ms (P < 0.01). The transmural dispersion of action potential duration significantly decreased from (128.7 +/- 13.5) ms to (54.3 +/- 10.8) ms (P < 0.01). Quinidine reduced pinacidil-induced transmural dispersion of phase 2 amplitude and the APD in right ventricular wall of canine.

CONCLUSIONBy restoring the dome and the APD of the epicardial and midcardial cells action potentials, quinidine (5 micromol/L) could reduce the marked transmural dispersion of repolarization caused by pinacidil.

Action Potentials ; drug effects ; Animals ; Dogs ; Heart Ventricles ; drug effects ; physiopathology ; Pinacidil ; pharmacology ; Quinidine ; pharmacology