Mackaay A J, Bleeker W K, Bouman L N
Recent Adv Stud Cardiac Struct Metab. 1976;11:51-5.
In the isolated right atrium of rabbit hearts, excess calcium causes an increase of heart rate at 38 degrees C; this effect is absent or even reversed at a temperature of 30 degrees C. From microelectrode studies it seems that when the calcium concentration is increased the pacemaker shifts within the sinoatrial node to cells in which excess calcium causes an acceleration of diastolic depolarization (type A). In fibers where the impulse originates at low calcium (type B), excess calcium causes a deceleration of diastolic depolarization. At low temperature, the effects on type A fibers are completely absent. Excess magnesium has a negative chronotropic effect at both temperatures, mainly by a deceleration of diastolic depolarization in type B fibers.
在兔心脏的离体右心房中，过量的钙在38℃时会导致心率增加；而在30℃时，这种效应不存在甚至会逆转。从微电极研究来看，当钙浓度增加时，窦房结内的起搏点会转移到过量的钙会导致舒张期去极化加速的细胞（A型）。在低钙时冲动起源的纤维（B型）中，过量的钙会导致舒张期去极化减速。在低温时，对A型纤维的影响完全不存在。过量的镁在两个温度下都有负性变时作用，主要是通过减慢B型纤维的舒张期去极化来实现。
