Discussion of "Why do some drugs preferentially block open sodium channels?": consideration of other significant factors in the binding process

The effects of propranolol on regional cardiac metabolism during ischemia and reperfusion assessed by magnetic resonance spectroscopy

Sixteen anesthetized New Zealand white rabbits were subjected to thoracotomy, and a reversible snare occluder was attached around a large branch of the left circumflex coronary artery. A 1.3 cm. diameter nuclear magnetic resonance (NMR) surface coil was placed adjacent to the myocardium perfused by this vessel. The animals were divided into two groups of eight animals each, treatment and control. The rabbits were studied using a 2.0 T magnetic resonance (MR) spectrometer, and baseline spectra were acquired. The treatment animals then received intravenous propranolol (1.5 mg/kg) and the control animals received an equal volume of saline. Spectra were then acquired during a 20-minute occlusion period and during subsequent reperfusion. Animals in both groups showed expected decreases in phosphocreatine and adenosine triphosphate and an increase in inorganic phosphate during occlusion; these changes reverted toward baseline values with reperfusion. There were no significant differences between the two groups. The myocardium became acidotic during occlusion in both groups, but significantly more so in the control animals: during the first 10 minutes of occlusion pH was 7.30 +/- 0.41 in the treatment group versus 6.55 +/- 0.24 for controls (p = 0.0005). During the second 10 minutes of occlusion pH was 7.05 +/- 0.65 in the treatment group versus 6.24 +/- 0.25 in controls (p = 0.0053). We conclude that attenuation of intracellular acidosis by propranolol during myocardial ischemia was evident by MR spectroscopy in this animal model.

Effects of antiarrhythmic agents classified as class III group on ischaemia-induced myocardial damage in canine hearts

1. The cardioprotective effects of antiarrhythmic agents classified as class III, amiodarone, sotalol and E-4031, were investigated in anaesthetized dogs. 2. The left anterior descending coronary artery was occluded for 2 h. 3. Heart mitochondria were prepared from both the ischaemic and non-ischaemic areas, and their function was estimated polarographically. 4. Activities of the lysosomal enzymes, N-acetyl-beta-glucosaminidase and beta-glucuronidase, were measured in each fraction. 5. Two hour occlusion induced ventricular arrhythmias, and amiodarone, sotalol and E-4031 greatly suppressed the development of arrhythmias. 6. Amiodarone, sotalol and E-4031 significantly protected mitochondria against ischaemia, and prevented ischaemia-induced leakage of lysosomal enzymes. 7. Antiarrhythmic agents classified as class III show cardioprotective effects, which might participate in their antiarrhythmic effect.