Horiuchi E, Hayashi H
Jpn J Physiol. 1979;29(5):569-83. doi: 10.2170/jjphysiol.29.569.
In order to examine the pH dependency of Cd effects on cardiac muscle, the electrical and mechanical activities in the bullfrog heart were investigated in relation to various external pHs and concentrations of Cd. The amplitude and duration of the action potential or the spontaneously beating frequency in the atrium were not significantly affected during the 3-min administration of various concentrations of Cd in a range from pH 6 to 10, but the isotonic contraction at the end of the same period was greatly altered: the lower the external pH the more Cd decreased the contractility of the atrium. This pH dependency of Cd effects was also observed in SO4-Ringer's solution whose anions, SO4, were more impermeable than Cl. Decrease in contractility in Cd-Ringer's solution was counteracted by excess Ca. The lower the pH of the Cd-Ringer's solution, the more Ca was necessary to counteract an equal amount of Cd. The amount of Cd-uptake into the atrium was analyzed after soaking the atrium in various concentrations of Cd-Ringer's solution. The higher the concentration of external Cd, the larger the Cd-uptake into the atrium. No pH dependency, however, was observed in this relationship. This suggests that probably only a small fraction of total Cd-uptake interacts with Ca-binding sites which is specific to contraction, and causes the Cd-induced decrease in contractility. This process is considered to be pH-dependent. However, most Cd-uptake into cardiac muscle is pH-independent and may be nonspecific to contraction.
为了研究镉对心肌影响的pH依赖性，研究了牛蛙心脏的电活动和机械活动与各种外部pH值和镉浓度的关系。在pH值为6至10的范围内，在3分钟内施用各种浓度的镉时，心房动作电位的幅度和持续时间或自发搏动频率没有受到显著影响，但在同一时期末的等张收缩却发生了很大变化：外部pH值越低，镉对心房收缩力的降低作用越大。在硫酸根林格氏液中也观察到了镉作用的这种pH依赖性，其阴离子硫酸根比氯离子更不易透过。镉林格氏液中收缩力的降低可被过量的钙抵消。镉林格氏液的pH值越低，抵消等量镉所需的钙就越多。将心房浸泡在各种浓度的镉林格氏液中后，分析了心房对镉的摄取量。外部镉的浓度越高，心房对镉的摄取量就越大。然而，在这种关系中未观察到pH依赖性。这表明，可能只有一小部分总镉摄取量与收缩特异性的钙结合位点相互作用，并导致镉诱导的收缩力降低。这个过程被认为是pH依赖性的。然而，大多数心肌对镉的摄取是pH非依赖性的，可能对收缩是非特异性的。
