ラット左・右心房筋におけるニコチンの変時・変力作用の比較

Abstract

Effects of nicotine on the sinus rate and the contractile force were investigated to compare the effects on the right and left atrial muscles of rats. Nicotine (300 μM and 1 mM) produced negative chronotropic and inotropic effects in the right atrium. The effects were dose-dependent. The maximum responses were caused about 30 sec after nicotine administration (1 mM), and the recovery period was almost 30 min. The depressive effects were not modified by 1 μM atropine. In the left atrial muscle, nicotine (300 μM and 1 mM) caused a negative inotropic effect. The muscle was electrically driven at different stimulations (1 to 3 Hz). The depression was decreased with an increase in stimulation frequencies (1 to 3 Hz). The negative inotropic effect reached its maximum in about 60 sec and persisted for 30 min. The negative responses to nicotine (1 mM) were stronger by 23% in the right atrium than in the left atrium stimulated at 3 Hz. There was no difference between the negative inotropic effects by single and cumulative administrations of nicotine in both right and left atrial muscles. These results suggest that the negative chronotropic and inotropic effects of nicotine may be due to a direct action on the cell membrane of rat atria, but not mediated through muscarinic and nicotinic acetylcholine receptors. The difference between the right and left atrial muscles might result from their characteristics for the sensitivity and/or binding sites of nicotine.