Effects of pirmenol on action potentials and membrane currents in single atrial myocytes

Characterization of the Pharmacology of YM-198313 on Volume-Regulated Anion Channels

Activation of the volume-regulated anion channels (VRAC) is considered to be involved in arrhythmia, but it has not yet been fully elucidated because of the lack of its high affinitive and selective compounds. A newly synthesized compound, YM-198313 (sodium 4-({[2-(methylthio)benzyl]amino}-5-[(1-phenylethyl)thio]isothiazol-3-olate), strongly inhibited VRAC in HeLa cells with an IC50 of 3.03+/-0.05 microM. However, YM-198313 weakly affected both the Ca2+-activated Cl- channels in HTC cells and the cAMP-activated Cl- channels in T84 cells, demonstrating that this compound is selective for VRAC among Cl- channels. At 10 microM, YM-198313 almost completely (100+/-7.8%) inhibited the VRAC current in guinea pig atrial myocytes. However, at the same concentration, YM-198313 showed little inhibitory effect on the cardiac cation currents in ventricular myocytes. We believe that YM-198313 is a potent and selective VRAC inhibitor, therefore, it should be use to clarify the role VRAC plays in arrhythmia.

Comparative actions of cibenzoline and disopyramide on I(Kr) and I(Ks) currents in rat sino-atrial nodal cells

Modulation by class Ia antiarrhythmic drugs, cibenzoline and disopyramide, of the pacemaking activity and the underlying ionic currents in rat sino-atrial nodal cells was investigated using current-clamp and whole-cell patch-clamp techniques. Both drugs depressed the spontaneous activity and often caused sinus arrest. The negative chronotropic effect was significant at 10 microM cibenzoline and 30 microM disopyramide. The L-type Ca(2+) current (I(Ca)) and the hyperpolarization-activated inward current decreased by 69.7+/-3.2% and by 45.8+/-3.0% at 30 microM cibenzoline and by 51. 2+/-3.3% and by 48.3+/-2.7% at 100 microM disopyramide, respectively. The delayed rectifier K(+) current, which is composed of rapidly and slowly activated currents (I(Kr) and I(Ks)), also decreased. The IC(50) values of I(Kr) for cibenzoline and disopyramide were 8.8+/-1. 1 and 25.1+/-2.3 microM, respectively. In the presence of 5 microM E-4031 (1-[2-(6-methyl-2-pyridyl)ethyl]-4-(4-methylsulfonylaminobenzoyl) piperidine), the IC(50) values of I(Ks) for cibenzoline and disopyramide were 12.3+/-1.8 and 81.1+/-2.3 microM, respectively. The I(Ks) was completely blocked by 30 microM 293B (trans-6-cyano-4-(N-ethylsulphonyl-N-methtamino)-3-hydroxy-2 , 2-dimethyl-chromane). These results indicate that the ionic currents are more sensitive to cibenzoline than disopyramide in rat sino-atrial nodal cells, and that I(Ca) and I(Kr) make major contributions to pacemaking activity.

Brugada syndrome characterized by the appearance of J waves

We describe a patient with Brugada syndrome. The ST-segment elevation in precordial leads was revealed during admission, but the appearance of J waves was characteristic before ventricular fibrillation (VF), rather than ST-segment elevation. J waves have been reported to be associated with the presence of an Ito-mediated prominent action potential notch in the epicardium. It is considered that one of the mechanisms of this VF is due to heterogeneous distribution of the refractory period according to changes in K+ channels including Ito.

Profiles of aprindine, cibenzoline, pilsicainide and pirmenol in the framework of the Sicilian Gambit. The Guideline Committee for Clinical Use of Antiarrhythmic Drugs in Japan (Working Group of Arrhythmias of the Japanese Society of Electrocardiology)

The Vaughan Williams classification has been used widely by clinicians, cardiologists and researchers engaged in antiarrhythmic drug development and testing in many countries throughout the world since its initial proposal in the early 1970s. However, a major criticism of the Vaughan Williams system arose from the extent to which the categorization of drugs into classes I-IV led to oversimplified views of both shared and divergent actions. The Sicilian Gambit proposed a two-dimensional tabular framework for display of drug actions to solve these problems. From April to December 1996, members of the Guideline Committee met to discuss pharmacologic profiles of 4 antiarrhythmic drugs (aprindine, cibenzoline, pilsicainide, and pirmenol) that were not included in the original spreadsheet but are used widely in clinical practice in Japan. The discussion aimed to fit the drug profiles into the Gambit framework based on all the important literature published to date regarding the actions of the 4 drugs. This report is a summary of that deliberation.