Grassl S M, Holohan P D, Ross C R
Department of Pharmacology, State University of New York, Syracuse 13210.
Biochim Biophys Acta. 1987 Dec 11;905(2):475-84. doi: 10.1016/0005-2736(87)90477-9.
Pathways for HCO3- transport across the basolateral membrane were investigated using membrane vesicles isolated from rat renal cortex. The presence of Cl(-)-HCO3- exchange was assessed directly by 36Cl- tracer flux measurements and indirectly by determinations of acridine orange absorbance changes. Under 10% CO2/90% N2 the imposition of an outwardly directed HCO3- concentration gradient (pHo 6/pHi 7.5) stimulated Cl- uptake compared to Cl- uptake under 100% N2 in the presence of a pH gradient alone. Mediated exchange of Cl- for HCO3- was suggested by the HCO3- gradient-induced concentrative accumulation of intravesicular Cl-. Maneuvers designed to offset the development of ion-gradient-induced diffusion potentials had no significant effect on the magnitude of HCO3- gradient-driven Cl- uptake further suggesting chemical as opposed to electrical Cl(-)-HCO3- exchange coupling. Although basolateral membrane vesicle Cl- uptake was observed to be voltage sensitive, the DIDS insensitivity of the Cl- conductive pathway served to distinguish this mode of Cl- translocation from HCO3- gradient-driven Cl- uptake. No evidence for K+/Cl- cotransport was obtained. As determined by acridine orange absorbance measurements in the presence of an imposed pH gradient (pHo 7.5/pHi 6), a HCO3- dependent increase in the rate of intravesicular alkalinization was observed in response to an outwardly directed Cl- concentration gradient. The basolateral membrane vesicle origin of the observed Cl(-)-HCO3- exchange activity was verified by experiments performed with purified brush-border membrane vesicles. In contrast to our previous observations of the effect of Cl- on HCO3- gradient-driven Na+ uptake suggesting a basolateral membrane Na+-HCO3- for Cl- exchange mechanism, no effect of Na+ on Cl-HCO3- exchange was observed in the present study.
利用从大鼠肾皮质分离的膜囊泡研究了HCO₃⁻跨基底外侧膜的转运途径。通过³⁶Cl⁻示踪剂通量测量直接评估Cl⁻-HCO₃⁻交换的存在，并通过测定吖啶橙吸光度变化间接评估。在10% CO₂/90% N₂条件下，与仅存在pH梯度时100% N₂条件下的Cl⁻摄取相比，向外的HCO₃⁻浓度梯度（pHo 6/pHi 7.5）的施加刺激了Cl⁻摄取。囊泡内Cl⁻的HCO₃⁻梯度诱导的浓缩积累提示了Cl⁻与HCO₃⁻的介导交换。旨在抵消离子梯度诱导的扩散电位发展的操作对HCO₃⁻梯度驱动的Cl⁻摄取幅度没有显著影响，这进一步表明是化学性的而非电性的Cl⁻-HCO₃⁻交换偶联。尽管观察到基底外侧膜囊泡的Cl⁻摄取对电压敏感，但Cl⁻传导途径对DIDS不敏感，这有助于将这种Cl⁻转运模式与HCO₃⁻梯度驱动的Cl⁻摄取区分开来。未获得K⁺/Cl⁻共转运的证据。在施加的pH梯度（pHo 7.5/pHi 6）存在下，通过吖啶橙吸光度测量确定，响应向外的Cl⁻浓度梯度，观察到囊泡内碱化速率有HCO₃⁻依赖性增加。用纯化的刷状缘膜囊泡进行的实验验证了观察到的Cl⁻-HCO₃⁻交换活性的基底外侧膜囊泡来源。与我们之前观察到的Cl⁻对HCO₃⁻梯度驱动的Na⁺摄取的影响（提示基底外侧膜存在Na⁺-HCO₃⁻与Cl⁻交换机制）相反，在本研究中未观察到Na⁺对Cl⁻-HCO₃⁻交换的影响。
