Kubota T, Fujimoto M
Jpn J Physiol. 1978;28(2):181-96. doi: 10.2170/jjphysiol.28.181.
In order to examine the seasonal changes in the relationship between the membrane potential and potassium activity of proximal tubular epithelium, a micropuncture study was performed with potassium selective microelectrodes on the kidney of the bullfrog (Rana catesbeiana) in two different seasons: winter (7 degrees C) and summer (20 degrees C). The potasssium activity in winter animals (7 degrees C) was 2.92 +/- 0.33 (mean +/- S.D., n = 20), 63.2 +/- 12.7 (n = 26), and 2.68 +/- 0.19 (n = 26) mM for the tubular fluid, cell, and plasma, whereas that in summer animals (20 degrees C) was 2.84 +/- 0.05 (n = 22), 61.8 +/- 11.2 (n = 24), 2.63 +/- 0.24 (n = 24) mM, respectively, indicating no seasonal difference. On the other hand, the mean values of the membrane PD in winter animals were 59.4 +/- 1.8 (n = 26) and 71.7 "/- 7.2 (n = 26) mV for the luminal and peritubular borders, whereas those in summer animals were 55.1 +/- 1.7 (n = 24) and 63.9 +/- 6.9 (n = 24) mV, respectivley, indicating that there was a significant seasonal difference (p less than 0.05 and p less than 0.001). Hence, compared to winter animals, the changes in the electrochemical profile for potassium in summer animals were: 1) the peritubular membrane PD is lower and 2) the transtubular electrochemical gradient is less steep. The sodium permeability calculated as the best fitting for a modified Goldman equation was 0.01 and 0.03 for winter and summer animals, respectively. In view of the fact the potassium in the cell and luminal fluid of the proximal tubule is kept at similar levels, potassium homeostasis is maintained in both groups of animals. The seasonal changes in electrical potentials are probably be due to an increase of cellular membrane permeability to ions other than potassium and to increased paracellular shunt conductance through the epithelium.
为了研究近端肾小管上皮细胞膜电位与钾活性之间关系的季节性变化，在两个不同季节（冬季7℃和夏季20℃），使用钾选择性微电极对牛蛙（牛蛙）肾脏进行了微穿刺研究。冬季动物（7℃）肾小管液、细胞和血浆中的钾活性分别为2.92±0.33（平均值±标准差，n = 20）、63.2±12.7（n = 26）和2.68±0.19（n = 26）mM，而夏季动物（20℃）的钾活性分别为2.84±0.05（n = 22）、61.8±11.2（n = 24）、2.63±0.24（n = 24）mM，表明无季节性差异。另一方面，冬季动物管腔和肾小管周围边界的膜电位平均值分别为59.4±1.8（n = 26）和71.7±7.2（n = 26）mV，而夏季动物的膜电位平均值分别为55.1±1.7（n = 24）和63.9±6.9（n = 24）mV，表明存在显著的季节性差异（p＜0.05和p＜0.001）。因此，与冬季动物相比，夏季动物钾的电化学分布变化为：1）肾小管周围膜电位较低；2）跨管电化学梯度较平缓。根据修正的戈德曼方程最佳拟合计算的钠通透性，冬季和夏季动物分别为0.01和0.03。鉴于近端小管细胞和管腔液中的钾保持在相似水平，两组动物均维持了钾稳态。电位的季节性变化可能是由于细胞膜对除钾以外的离子通透性增加以及上皮细胞旁细胞分流电导增加所致。
