Na+/HCO3-co-transport in basolateral membrane vesicles isolated from rabbit renal cortex.
Na+/HCO3-co-transport in basolateral membrane vesicles isolated from rabbit renal cortex.
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DOI：
10.1016/s0021-9258(19)84448-4
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发表时间：
1986-07
期刊：
影响因子：
--
通讯作者：
S. Grassl;P. Aronson
中科院分区：
文献类型：
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作者：
S. Grassl;P. Aronson
最近的研究表明，HCO3-穿过近端小管细胞基底膜的主要途径是电生Na+/HCO3-共转运。因此，我们评估了从兔肾皮质分离的基底侧膜囊泡中存在Na+/HCO3-共转运的可能性。施加向内的HCO3-梯度诱导Na+的瞬时上行积累，施加向外的Na+梯度导致依赖于HCO3的内酸pH梯度的产生，这与Na+/HCO3-共转运的存在是一致的。在没有其他驱动力的情况下，通过向内施加K+梯度来产生膜内正电电位，并在呋喃霉素存在的情况下，通过HCO3依赖的途径引起净Na+摄取，这表明Na+/HCO3-共转运是产生电的，并与负电荷流有关。施加跨膜Cl-梯度对HCO3-梯度刺激的Na+内流没有显著影响，表明Na+/HCO3-共转运不依赖于Cl-。HCO3梯度刺激的Na+内流速率是Na+浓度(Km=9.7 mM，Vmax=160nmol/min/mg蛋白质)的简单可饱和函数，可被4，4‘-二异硫氰基二苯乙烯-2，2’-二磺酸(I50=100微米)抑制，但1 mM的阿米洛利抑制不到10%。在微绒毛膜囊泡中，未发现HCO3依赖或4，4‘-二异硫氰基二苯乙烯-2，2’-二磺酸敏感的Na+内流成分。因此，本研究表明，从兔肾皮质分离的膜囊泡中存在一种运输系统，该转运系统介导了基底外侧膜小泡的Na+/HCO3-共转运，而不是腔内膜泡。与用肾微绒毛膜囊研究Na~+/H~+交换类似，肾基底侧膜囊泡可能是研究Na~+/HCO3~-共转运动力学和可能调节的模型系统。
Recent studies suggest that the major pathway for exit of HCO3- across the basolateral membrane of the proximal tubule cell is electrogenic Na+/HCO3- co-transport. We therefore evaluated the possible presence of Na+/HCO3- co-transport in basolateral membrane vesicles isolated from the rabbit renal cortex. Imposing an inward HCO3- gradient induced the transient uphill accumulation of Na+, and imposing an outward Na+ gradient caused HCO3- -dependent generation of an inside-acid pH gradient as monitored by quenching of acridine orange fluorescence, findings consistent with the presence of Na+/HCO3- co-transport. In the absence of other driving forces, generating an inside-positive membrane potential by imposing an inward K+ gradient in the presence of valinomycin caused net Na+ uptake via a HCO3- -dependent pathway, indicating that Na+/HCO3- co-transport is electrogenic and associated with a flow of negative charge. Imposing transmembrane Cl- gradients did not appreciably affect HCO3- gradient-stimulated Na+ influx, suggesting that Na+/HCO3- co-transport is not Cl- -dependent. The rate of HCO3- gradient-stimulated Na+ influx was a simple, saturable function of the Na+ concentration (Km = 9.7 mM, Vmax = 160 nmol/min/mg of protein), was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (I50 = 100 microM), but was inhibited less than 10% by up to 1 mM amiloride. We could not demonstrate a HCO3- -dependent or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive component of Na+ influx in microvillus membrane vesicles. This study thus indicates the presence of a transport system mediating electrogenic Na+/HCO3- co-transport in basolateral, but not luminal, membrane vesicles isolated from the rabbit renal cortex. Analogous to the use of renal microvillus membrane vesicles to study Na+/H+ exchange, renal basolateral membrane vesicles may be a useful model system for examining the kinetics and possible regulation of Na+/HCO3- co-transport.