Search

The negative inotropic effects of nine Vaughan Williams class I antiarrhythmic drugs were examined in guinea pig ventricular tissue preparations. The drugs decreased the contractile force of papillary muscles with different potencies: the potency order was propafenone > aprindine > cibenzoline > flecainide > ranolazine > disopyramide > pilsicainide > mexiletine > GS-458967. The potency of drugs correlated with the reported IC 50 values to block the L-type Ca 2+ channel rather than the Na + channel. The effects of drugs were roughly the same when examined under a high extracellular K + solution, which inactivates the Na + channel. Furthermore, the attenuation of the extracellular Ca 2+ -induced positive inotropy was strong with propafenone, moderate with cibenzoline, and weak with pilsicainide. These results indicate that the negative inotropic effects of class I antiarrhythmic drugs can be largely explained by their blockade of the L-type Ca 2+ channel.

The effect of blocking the persistent component of the sodium channel current (late I Na ) on the automatic activity of the isolated guinea pig pulmonary vein myocardium was examined. NCC-3902 blocked late I Na , but did not affect other major ion channel currents stably expressed in cell lines. In isolated pulmonary vein cardiomyocytes, NCC-3902 blocked the late I Na induced by a ramp depolarizing voltage clamp pulse similar to that of the pacemaker depolarization observed in the pulmonary vein myocardium. In isolated pulmonary vein tissue, NCC-3902 decreased the frequency of automatic firing of the myocardium through a reduction of the pacemaker depolarization slope. In isolated pulmonary vein cardiomyocytes, NCC-3902 significantly reduced the firing frequency of Ca 2+ transients, but had no effect on Ca 2+ sparks. NCC-3902 affected neither the spontaneous beating rate of the right atrium nor the contractile force of the ventricular myocardium. Selective blockers of late I Na like NCC-3902, which inhibit the automatic activity of the pulmonary vein myocardium, appear to be promising as drugs for the pharmacological treatment of atrial fibrillation.

We developed a method to evaluate the activity of the Na + -Ca 2+ exchanger (NCX) and sarco-endoplasmic reticulum Ca 2+ -ATPase (SERCA) with fluorescence microscopy in mouse ventricular cardiomyocytes. In non-beating ventricular cardiomyocytes, α-adrenoceptor stimulation by phenylephrine caused a decrease in the cytoplasmic Ca 2+ concentration, which was inhibited by SEA0400, an NCX inhibitor, but not cyclopiazonic acid, a SERCA inhibitor. β-Adrenoceptor stimulation by isoprenaline caused a decrease in the cytoplasmic Ca 2+ concentration, which was inhibited by cyclopiazonic acid but not SEA0400. Ellagic acid, a phenolic phytochemical, also decreased the basal Ca 2+ concentration, which was inhibited by cyclopiazonic acid, but not SEA0400. Thus, this method using fluorescent microscopy and specific inhibitors would be useful for the evaluation of pharmacological agents acting on NCX and SERCA.

The lusitropic effect of quercetin was examined on isolated ventricular myocardial tissue preparations from normal and streptozotocin-induced diabetic mice. The time required for 90% relaxation of the myocardium, which was prolonged in the diabetic mice, was shortened by quercetin in both normal and diabetic myocardia. This effect of quercetin was completely inhibited by cyclopiazonic acid but not by SEA0400. These results indicated that quercetin accelerates myocardial relaxation through activation of the sarco-endoplasmic reticulum Ca 2+ -ATPase.

The functional role of ATP released from sympathetic nerve terminals was examined in isolated guinea pig ventricular papillary muscles. The contractile force of papillary muscles was increased by field electrical stimulation of sympathetic nerve endings. This increase was attenuated by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) or suramin, blockers of the P2X receptor, and was abolished by propranolol and prazosin. PPADS, suramin, and ATP affected neither the basal contractile force nor the positive inotropic effect of noradrenaline. These results provide functional evidence that ATP released from sympathetic nerve terminals enhances noradrenaline release and contributes to sympathetic nerve-induced inotropy.

The effect of KB-R7943, an inhibitor of the plasmalemmal Na + -Ca 2+ exchanger, on mitochondrial Ca 2+ transporters was examined with membrane-permeabilized cardiomyocyte-derived H9c2 cells expressing the fluorescent Ca 2+ indicator, yellow cameleon 3.1, in the mitochondria. KB-R7943, as well as ruthenium red, inhibited the rise in mitochondrial Ca 2+ on increasing the extramitochondrial Ca 2+ concentration from 0 nM to 300 nM. CGP-37157, but not KB-R7943, inhibited the decline in mitochondrial Ca 2+ on return to Ca 2+ free extramitochondrial solution. These results indicated that KB-R7943 has inhibitory effects on the mitochondrial Ca 2+ uniporter, but not on the mitochondrial Na + -Ca 2+ exchanger.

The presence and function of the ATP-sensitive potassium channel current (I KATP ) were examined in the guinea pig myocardium to clarify the mechanisms for the resistance of the fetal myocardium to hypoxia. Experimental hypoxia markedly reduced the action potential duration and contractile force in isolated ventricular myocardium from the adult, but only moderately in those from the fetus. In isolated ventricular cardiomyocytes, the density of the I KATP activated by cromakalim, as well as their sensitivity to intracellular ATP concentration, were not different between the fetus and adult. The tissue ATP content was similar between the fetal and adult myocardium under normal condition, but the hypoxia-induced decrease was smaller in the fetus. Confocal microscopic analysis revealed that the mitochondria in the fetal cardiomyocyte is less in quantity than that in the adult and is more localized to the cell center. These results indicate that I KATP in the fetal guinea pig myocardium has a current density and ATP sensitivity similar to those of the adult, but is not activated under hypoxic conditions because the energy metabolism of the fetal myocardium is less dependent on oxidative phosphorylation.

We investigated the effect on mitochondrial Ca 2+ of SEA0400, an inhibitor of the Na + /Ca 2+ exchanger (NCX) which reduces mitochondrial Ca 2+ overload during myocardial ischemia, in digitonin-permeabilized H9c2 cells expressing the mitochondrial-targeted Ca 2+ indicator, yellow cameleon 3.1. The elevation of mitochondrial Ca 2+ concentration caused by an increase in extramitochondrial Ca 2+ concentration was inhibited by carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) or ruthenium red, but enhanced by CGP-37157, a mitochondrial NCX inhibitor. SEA0400 had no effect on mitochondrial Ca 2+ under normal and ischemic conditions. Thus, the mitochondria-protective effects of SEA0400 could be explained by inhibition of plasmalemmal NCX but not mitochondrial NCX.

The effects of mechanical stretch on the automaticity of the guinea pig isolated pulmonary vein preparations were studied in microelectrode experiments. The application of cumulative mechanical stretch to the preparations resulted in increases in the firing rate of spontaneous electrical activity in the myocardial layer. This effect was significantly inhibited by stretch-activated channel blockers such as gadolinium or streptomycin. These results suggest that acute mechanical stretch enhances the automaticity of the guinea pig pulmonary vein myocardium through the opening of the stretch-activated channels.

We examined the effects of SEA0400 and CGP-37157 on the plasmalemmal Na(+)-Ca(2+) exchanger (NCX) and mitochondrial NCX using H9c2 cardiomyocytes loaded with Ca(2+)-sensitive fluorescent probes. The plasmalemmal NCX activity, which was measured as the increase in cytoplasmic Ca(2+) concentration after application of low Na(+) extracellular solution, was inhibited by SEA0400 but not by CGP-37157. The mitochondrial NCX activity, which was measured in permeabilized H9c2 cells as the decrease in mitochondrial Ca(2+) concentration after application of Ca(2+)-free extramitochondrial solution, was inhibited by CGP-37157 but not by SEA0400. These results indicate that SEA0400 and CGP-37157 act as selective inhibitors towards plasmalemmal and mitochondrial NCX, respectively, and provide pharmacological evidence that the plasmalemmal and mitochondrial NCX are distinct molecular entities.

An outbreak of Multi-Drug Resistance Pseudomonas aeruginosa (MDRP) infections occurred in intensive care unit (ICU) and emergency room (ER) between June and August 2007. Five patients who isolated MDRP in the outbreak of 2007 were all used bronchoscopes, thus, we suspected contamination of the bronchoscopes as the cause of outbreak. Although we did not detect MDRP from any bronchoscopes, the outbreak finally ended after all the bronchoscopes had been disinfected appropriately with the reexamination of washing process in 2008 and 2009. We retrospectively reviewed eleven patients who isolated MDRP in 2006 and 2007, and the fact was revealed that bronchoscopes were used in most patients in ICU and ER. Bronchoscopes were significantly used during 2006-2007 period, compared with 2008-2009 period in ICU and ER, and the case-control analysis among all Pseudomonas aeruginosa isolated patients identified that bronchoscopes [risk ratio (RR) 8.25, 95% confidence interval (CI) 1.328-51.26] was one of the most important risk factors for MDRP isolation. Duration from admission to MDRP isolation was significant longer in MDRP-isolated cases (19.82±12.77 d), compared with in non MDRP-isolated controls (11.76±11.69 d: p=0.0453). Our epidemiological analysis suggested the significant risk factors for an MDRP outbreak, and could contribute the estimation of the focus and prevention of future outbreaks.

The effects of terfenadine and pentamidine on the human ether-a-go-go related gene (hERG) channel current and its intracellular trafficking were evaluated. Green fluorescent protein (GFP)-linked hERG channels were expressed in HEK293 cells, and the membrane current was measured by an automated whole cell voltage clamp system. To evaluate drug effects on channel trafficking to the cell membrane, the fraction of channel present on the cell membrane was quantified by current measurement after drug washout and confocal microscopy. Terfenadine directly blocked the hERG channel current but had no effect on trafficking of hERG channels to the cell membrane after application in culture medium for 2 d. In contrast, pentamidine had no direct effect on the hERG channel current but reduced trafficking of hERG channels. The two drugs inhibited hERG channel function through different mechanisms: terfenadine through direct channel blockade and pentamidine through inhibition of channel trafficking to the cell membrane. Combined use of automated voltage clamp and confocal microscopic analyses would provide insights into the mechanisms of drug-induced QT-prolongation and arrhythmogenesis.

This study aimed to clarify the efficacy, safety, and pharmacokinetics of piperacillin–tazobactam (PIPC– TAZ) in late elderly Japanese patients. This is the first antimicrobial pilot study in late elderly patients with nursing and healthcare associated pneumonia. After PIPC–TAZ administration, PIPC concentrations in plasma were measured chromatographically and the pharmacokinetic parameters were estimated. Efficacy, safety, and bacteriological evaluations were also carried out. The mean age was 85.0 years old and most of the patients were late elderly. Chest X-rays, body temperature, white blood cell count, and C reactive protein all improved significantly, and a high efficacy ratio of 90.9% was observed. Serious nephrotoxicity was observed in 4 cases (18.2%) after administration of PIPC–TAZ. Creatinine clearance (meanS.D.) measured before PIPC–TAZ therapy was significantly lower in the nephrotoxicity group (32.54.4 mL/min) than in the non-nephrotoxicity group (46.116.7 mL/min), although the ages were not different between the 2 groups. In the pharmacokinetic parameters for PIPC, total clearance was slightly lower in the nephrotoxicity group than in the non-nephrotoxicity group. However, no significant difference was observed in plasma PIPC levels between the 2 groups. In patients with renal impairment, especially with a creatinine clearance of <40 mL/ min, renal impairment was found to be an influencing factor for severe nephrotoxicity following PIPC–TAZ administration. In conclusion, the results suggest that physicians should pay close attention in order to avoid possible toxicity, and that deliberate administration planning and careful follow-up are required in late elderly patients with comprised organ dysfunction.

Effects of NIP-142, a benzopyran compound which terminates experimental atrial arrhythmia, on potassium channel alpha-subunits and mouse atrial repolarization were examined. NIP-142 concentration-dependently blocked the outward current through potassium channel alpha subunits Kv1.5, Kv4.2 and Kv4.3 expressed in Xenopus oocytes. In isolated mouse atrial myocardia, NIP-142 prolonged the action potential duration and effective refractory period, and increased the contractile force. These results suggest that NIP-142 blocks the potassium channels underlying the transient and sustained outward currents, which may contribute to its antiarrhythmic activity.