羊心浦肯野纤维钠泵活动与动作电位长度关系

On the Relationship Between Sodium—Pump and Action Potential Duration in Cardiac Purkinje Fibres

采用羊心浦肯野纤维标本,间断地施以快速刺激,用普通玻璃微电极与离子选择电极同时记录细胞动作电位(AP)、细胞内 Na^+ 活度(a_(Na)~i)及细胞间 K^+ 活度(a_k^0).或者,在固定频率刺激下将标本短时间置于无 K^+ 液中作预处理,以提高 a_(Na)~i,刺激钠泵活动.目的在于观察细胞膜钠泵活动及跨膜被动K^+ 流在 APD 变化中的调控作用.结果表明,在心率的生理范围内(60～150次/min),致电钠泵电流在总复极电流中占12%～15%。

Measurements of the intracellular sodium activity(a_(Na)~i,as a indicator of sodium-pump activity)and the paracellular potassium activity(a_K^0)were performed in sheep cardiac Purkin- je fibres at rest and during stimulation using ion-selective microelectrodes.During a period of stimulation,paracellular potassium first increased and then declined below control values as long as pump activity was enhanced.The time course of the maximal diastolic potential was similar to pump activity,whereas that of the action potential duration deviated markedly. Further experiments on the effect of pump activation following challenges to zero potassium solution revealed that the rate dependence of the action potential duration was more sensitive to extracellular calcium than it was to the pump activity.Quantitative analysis of the data showed that in the physiological range of heart rate(60～150/min),the contribution of the electrogenic pump current to total repolarizing currents is between 12% and 25%.