Ryan T E, Barr C E, Zorn J P
J Gen Physiol. 1978 Aug;72(2):203-18. doi: 10.1085/jgp.72.2.203.
Transmembrane movements of K+ and Cl- were studied under a variety of experimental conditions. Potassium was found to carry more than 50% of an externally applied inward positive current. The increase in K+ influx was much greater than that predicted by the purely passive model. The increase in Cl- efflux accounted for less than 10% of the applied current, in agreement with the value predicted for passive movement. 2,4-Dinitrophenol (DNP) caused an 80% reduction in K+ transference and a corresponding increase in the measured electrical resistance of the membrane. DNP also reduced the isotopically measured resting K+ influx and caused a substantial increase in both Cl- influx and efflux. Lowering of the pH from 5.7 to 4.7 also reduced the net K+ influx but without drastically altering the membrane resistance. It appears the major portion of an externally applied current does not travel through passive channels, but rather is shunted through a different membrane component. In conjunction with evidence previously establishing the H+ pump as the primary ion pump in Nitella, the data presented here are consistent with a K+/H+ exchange mechanism which can account for the observed net K+ accumulation and maintenance of the membrane potential above the electrochemical equilibrium potential of the major ions. This mechanism appears to be a likely candidate for the current shunt.
在各种实验条件下研究了钾离子（K⁺）和氯离子（Cl⁻）的跨膜运动。发现钾离子携带超过50%的外部施加的内向正电流。钾离子内流的增加远大于纯被动模型预测的增加量。氯离子外流的增加占施加电流的比例不到10%，这与被动运动预测的值一致。2,4 - 二硝基苯酚（DNP）使钾离子转运减少80%，并使测得的膜电阻相应增加。DNP还降低了同位素测量的静息钾离子内流，并导致氯离子内流和外流都大幅增加。将pH从5.7降至4.7也降低了净钾离子内流，但没有显著改变膜电阻。似乎外部施加电流的主要部分不是通过被动通道传输，而是通过不同的膜成分分流。结合先前确立氢离子泵作为丽藻主要离子泵的证据，此处呈现的数据与钾离子/氢离子交换机制一致，该机制可以解释观察到的净钾离子积累以及膜电位维持在主要离子的电化学平衡电位之上的现象。这种机制似乎是电流分流的一个可能候选者。
