Ishibashi K, Rector F C, Berry C A
Department of Physiology and Medicine, University of California, San Francisco 94143.
Am J Physiol. 1993 Feb;264(2 Pt 2):F251-8. doi: 10.1152/ajprenal.1993.264.2.F251.
To analyze the rate of basolateral Cl exit and the magnitude and relative contributions of KCl cotransport and Na-dependent and -independent Cl/HCO3 exchange to Cl exit across the basolateral membrane (BLM) during transcellular Cl absorption, rabbit proximal convoluted tubules (PCT) were perfused with high-Cl, low-HCO3 plus formate solutions and bathed with plasma ultrafiltrate-like plus formate solutions. The initial rates of intracellular Cl activity (AiCl) reduction following bath Cl removal were compared when bath Cl was 0, when bath Na and Cl were 0, and when bath HCO3 and Cl were 0. The initial rate of AiCl reduction following bath Cl removal was 4.4 +/- 0.4 mM/s. After bath Na and Cl removal, this rate was reduced to 25.1 +/- 5.0%. After bath HCO3 and Cl removal, it was reduced to 18.0 +/- 4.8%. The difference between bath Na and Cl removal and bath HCO3 and Cl removal was not significant. Cl efflux following bath HCO3 and Cl removal may be due to a KCl symporter. The contribution of a KCl symporter was examined by raising bath K to 20 mM, thus eliminating the chemical driving force for KCl exit. After bath K increase, the initial rate of AiCl increase was 0.057 +/- 0.005 mM/s. These data suggest that Cl efflux at BLM of rabbit PCT is 1) large enough to explain transcellular Cl transport, 2) predominately due to an Na-dependent Cl/HCO3 exchanger, and 3) negligibly due to an Na-independent Cl/HCO3 exchanger or a KCl symporter.
为分析在跨细胞氯吸收过程中，基底外侧膜（BLM）氯流出速率以及氯化钾共转运、钠依赖性和非依赖性氯/碳酸氢根交换对跨基底外侧膜氯流出的幅度和相对贡献，用高氯、低碳酸氢根加甲酸盐溶液灌注兔近端肾小管（PCT），并用类似血浆超滤液加甲酸盐溶液进行浴灌流。比较在浴灌流氯为0、浴灌流钠和氯为0以及浴灌流碳酸氢根和氯为0时，浴灌流氯去除后细胞内氯活性（AiCl）降低的初始速率。浴灌流氯去除后AiCl降低的初始速率为4.4±0.4 mM/s。浴灌流钠和氯去除后，该速率降至25.1±5.0%。浴灌流碳酸氢根和氯去除后，降至18.0±4.8%。浴灌流钠和氯去除与浴灌流碳酸氢根和氯去除之间的差异不显著。浴灌流碳酸氢根和氯去除后的氯外流可能归因于氯化钾同向转运体。通过将浴灌流钾提高到20 mM来检查氯化钾同向转运体的贡献，从而消除氯化钾流出的化学驱动力。浴灌流钾增加后，AiCl增加的初始速率为0.057±0.005 mM/s。这些数据表明，兔PCT基底外侧膜的氯外流：1）大到足以解释跨细胞氯转运；2）主要归因于钠依赖性氯/碳酸氢根交换体；3）因非钠依赖性氯/碳酸氢根交换体或氯化钾同向转运体导致的氯外流可忽略不计。
