Sodium current in single internally perfused myocardial cells. Effects of ethmozine and lidocaine.
Voltage-clamp experiments were carried out, and sodium current (INa) was recorded on single rat cardiac cells perfused internally with Ca2+-free 140 mM Tris aspartate, 2 mM EGTA buffer, pH 7.3 at 20 degrees C. A voltage control microelectrode was impaled in the cell. Ethmozine (E), 0.08 mg/ml, and lidocaine (L), 0.08 mg/ml, were tested both inside and outside the cells. Although practically ineffective when administered inside the cell, E markedly affected INa when used externally. After 5 min of E treatment, the maximal INa was diminished to 43 +/- 6% (N = 6) of control value without any significant changes in the reactivation time constant tau re. Extra- and intracellular effects of L on INa were nearly equal. Internal L reduced the maximal INa to 31 +/- 5% (N = 7) of its initial value in 5 min; longer periods (8-10 min) were needed to obtain a similar effect with externally added L. Diminution of INa was accompanied by a delay in recovery; after 8 min of external L action, tau re increased from 17.5 +/- 1.7 msec (N = 4) to 142.5 +/- 19.9 msec (N = 4). It is supposed that ethmozine and lidocaine act at different sites on the cellular membrane.
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006352:Heart Ventricles / Q000187:drug effects; D007473:Ion Channels / Q000187:drug effects*; D007700:Kinetics; D008012:Lidocaine / Q000494:pharmacology*; D008855:Microscopy, Electron, Scanning; D016293:Moricizine; D010477:Perfusion; D010640:Phenothiazines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D000889:Anti-Arrhythmia Agents; D007473:Ion Channels; D010640:Phenothiazines; D016293:Moricizine; D008012:Lidocaine; D012964:Sodium