Glitsch H G, Krahn T, Pusch H
Department of Cell Physiology, Ruhr-University Bochum, Federal Republic of Germany.
Pflugers Arch. 1989 May;414(1):52-8. doi: 10.1007/BF00585626.
The effect of various intracellular Na concentrations (CiNa) and membrane potentials on the Na pump current (Ip) was studied in isolated, cultured sheep cardiac Purkinje cells ('cardioballs'). Ip was identified as cardiac steroid sensitive current. The dependence of Ip on CiNa was investigated at a membrane potential of -40 mV by means of whole-cell recording from cardioballs internally perfused with media containing various Na concentrations. Internal perfusion with a Na free solution abolished Ip. The amplitude of Ip as a function of CiNa displayed saturation kinetics. Half maximal activation of Ip occurred at a CiNa of about 9 mM. The maximal Ip density was estimated to be 1.1 microA/cm2. The potential dependence of Ip was studied by conventional whole-cell recording under various ionic conditions. Generally Ip displayed little voltage dependence at membrane potentials positive to -20 mV. Ip declined at more negative potentials. The pump cycle probably includes only one voltage sensitive step. The potential dependence of Ip was more pronounced at lower CiNa or lower concentrations of the external pump activator Cs+. The findings are in line with the idea that increasingly steeper ionic gradients against which the cations are pumped strengthen the voltage dependence of Ip in the potential range studied. Other factors probably affecting the pump current-voltage (Ip-V) relation are discussed. The results suggest that Ip varies during electrical activity.
在分离培养的绵羊心脏浦肯野细胞（“心肌球”）中研究了各种细胞内钠浓度（CiNa）和膜电位对钠泵电流（Ip）的影响。Ip被确定为对心脏甾体敏感的电流。通过对内部灌注含不同钠浓度培养基的心肌球进行全细胞记录，在膜电位为-40 mV时研究了Ip对CiNa的依赖性。用无钠溶液进行内部灌注可消除Ip。Ip的幅度作为CiNa的函数呈现饱和动力学。Ip的半数最大激活发生在CiNa约为9 mM时。估计最大Ip密度为1.1微安/平方厘米。在各种离子条件下，通过传统的全细胞记录研究了Ip的电位依赖性。一般来说，在膜电位高于-20 mV时，Ip对电压的依赖性很小。在更负的电位下，Ip下降。泵循环可能只包括一个电压敏感步骤。在较低的CiNa或较低浓度的外部泵激活剂Cs +时，Ip对电位的依赖性更明显。这些发现与这样的观点一致，即在研究的电位范围内，阳离子被泵出时离子梯度越来越陡峭，从而增强了Ip对电压的依赖性。还讨论了可能影响泵电流-电压（Ip-V）关系的其他因素。结果表明，Ip在电活动期间会发生变化。
