Voltage dependence of the Na-K pump.
Voltage dependence of the Na-K pump.
复制标题
Na-K 泵的电压依赖性。
DOI：
10.1146/annurev.ph.50.030188.001301
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发表时间：
1988
影响因子：
18.2
通讯作者：
Rakowski,RF
中科院分区：
文献类型：
--
作者：
DeWeer,P;Gadsby,DC;Rakowski,RF
目前的证据表明，钠钾泵速率是电压依赖性的，而早期的工作在很大程度上是不确定的。IV关系在宽电压范围内具有正斜率，并且负斜率区域的存在现在是可疑的。单调的电压依赖性与包含单个电压依赖性步骤的反应循环一致。最近的测量结果表明，这一电压依赖性步骤发生在Na易位过程中，可能是Na+的去闭塞。此外，两个结果表明，K易位是电压不敏感的：（a）大的正电位似乎没有影响Rb-Rb交换或相关的构象转变;和（B）与Na易位相关的瞬态电流似乎涉及一个单一的电荷，这是足够的3 Na-2 K循环的运动。最简单的解释是泵的阳离子结合位点提供两个负电荷。前稳态测量表明，钠易位之前泵循环的限速步骤，大概是K易位。但是，因为K易位似乎电压不敏感，稳态泵速率的电压依赖性可能反映了进入这个缓慢步骤的中间体的浓度。进一步的泵电流和通量数据（瞬态和稳态），仔细确定了一系列的条件下，应该增加我们的理解的电压依赖性步骤（S）在钠钾泵循环。
Present evidence demonstrates that the Na-K pump rate is voltage dependent, whereas early work was largely inconclusive. The IV relationship has a positive slope over a wide voltage range, and the existence of a negative slope region is now doubtful. Monotonic voltage dependence is consistent with the reaction cycle containing a single voltage-dependent step. Recent measurements suggest that this voltage-dependent step occurs during Na translocation and may be deocclusion of Na+. In addition, two results suggest that K translocation is voltage insensitive:(a) large positive potentials appear to have no influence on Rb-Rb exchange or associated conformational transitions; and (b) transient currents associated with Na translocation appear to involve movement of a single charge, which is sufficient for a 3Na-2K cycle. The simplest interpretation is that the pump's cation binding sites supply two negative charges. Pre-steady-state measurements demonstrate that Na translocation precedes the pump cycle's rate-limiting step, presumably K translocation. But, because K translocation seems voltage insensitive, the voltage dependence of the steady-state pump rate probably reflects that of the concentration of the intermediate entering this slow step. Further pump current and flux data (both transient and steady-state), carefully determined over a range of conditions, should increase our understanding of the voltage-dependent step (s) in the Na-K pump cycle.