Busch A E, Herzer T, Waldegger S, Schmidt F, Palacin M, Biber J, Markovich D, Murer H, Lang F
Institute of Physiology, Eberhard-Karls-Universität Tübingen, Federal Republic of Germany.
J Biol Chem. 1994 Oct 14;269(41):25581-6.
Voltage- and current-clamp studies have been performed on a renal and intestinal protein (rBAT) which induces transport for neutral and dibasic amino acids when expressed in Xenopus oocytes. In current-clamp mode, superfusion with L-leucine caused a hyperpolarization while superfusion with L-arginine depolarized the oocyte. Accordingly, in voltage-clamp experiments dibasic amino acids and neutral amino acids induced inward and outward currents, respectively. The relationship between currents and substrate concentrations could be fitted by simple Michaelis-Menten kinetics. Currents induced by L-arginine and L-leucine were also voltage-dependent. pH changes from 6.25 to 8.75 did not affect the currents induced by saturating concentrations of L-arginine and L-leucine, but reversed the direction of L-histidine-induced currents from inward to outward. The reversal potentials as well as the apparent Km for L-histidine-induced currents were altered by the ambient pH. Currents induced by individual amino acids decreased during extended superfusion periods. However, extended superfusion with neutral amino acids increased dibasic amino acid induced currents, while prior superfusion with dibasic amino acid resulted in an increase of currents induced by neutral amino acids. The reversal potentials for L-leucine- and L-arginine-induced currents were depending on their intra- (after preloading) and extracellular concentrations. In conclusion, rBAT-mediated transport of neutral and dibasic amino acids is associated with net outward or inward currents, respectively, which may be caused by an exchange of neutral with dibasic amino acids.
已对一种肾脏和肠道蛋白（rBAT）进行了电压钳和电流钳研究，该蛋白在非洲爪蟾卵母细胞中表达时可诱导中性和二碱基氨基酸的转运。在电流钳模式下，用L-亮氨酸灌注会导致超极化，而用L-精氨酸灌注则会使卵母细胞去极化。因此，在电压钳实验中，二碱基氨基酸和中性氨基酸分别诱导内向和外向电流。电流与底物浓度之间的关系可用简单的米氏动力学来拟合。L-精氨酸和L-亮氨酸诱导的电流也与电压有关。pH值从6.25变化到8.75并不影响饱和浓度的L-精氨酸和L-亮氨酸诱导的电流，但会使L-组氨酸诱导的电流方向从内向变为外向。L-组氨酸诱导电流的反转电位以及表观Km会因环境pH值而改变。在长时间灌注期间，单个氨基酸诱导的电流会降低。然而，用中性氨基酸长时间灌注会增加二碱基氨基酸诱导的电流，而先用二碱基氨基酸灌注则会导致中性氨基酸诱导的电流增加。L-亮氨酸和L-精氨酸诱导电流的反转电位取决于它们的细胞内（预加载后）和细胞外浓度。总之，rBAT介导的中性和二碱基氨基酸转运分别与净外向或内向电流相关，这可能是由中性氨基酸与二碱基氨基酸的交换引起的。
