Lapkin R, Bowman R, Kaloyanides G J
J Pharmacol Exp Ther. 1977 Apr;201(1):233-42.
The mechanism by which gentamicin augments the uptake of p-aminohippurate (PAH) by rat renal cortical slices was investigated. In all experiments, gentamicin was administered as gentamicin sulfate at 100 mg/kg b.wt. per day for 2 days; control rats were injected with saline. The effect of gentamicin on the metabolism of PAH to p-aminobenzoic acid (PABA), acetyl-PABA and acetyl-PAH was studied by high performance liquid chromatography. No metabolites of PAH were detected in renal slices of gentamicin-injected or control rats incubated in medium containing PAH. Efflux of 14C-PAH was measured after incubating renal cortical slices for 2 hours in medium containing 8 X 10(-5) M 14C-PAH. The efflux rate constant was 0.080 +/- 0.003/min in control slices and 0.059 +/- 0.003/min in gentamicin slices, P less than .001. No significant difference in the diffusible pool of PAH was found between the two groups which supports an argument against increased tissue-binding of PAH as the explanation for the augmented uptake of PAH by slices of gentamicin-injected rats. Active PAH transport was assessed in terms of Michaelis-Menten kinetics. Vmax was 0.93 +/- 0.08 micronmol/g/15 min in control slices and 1.37 +/- 0.10 micronmol/g/15 min in gentamicin slices (P less than .005). The apparent reaction rate constant (Km) was not different; Km was 0.25 +/- 0.03 and 0.29 +/- 0.04 mM in control and gentamicin slices, respectively (P less than .4). In contrast to PAH, gentamicin did not alter uptake of N'-methynicotinamide, an organic base; nor did it alter the efflux rate constant or diffusible pool of N'-methylnicotinamide. Increased PAH uptake was still evident when slices of gentamicin-injected rats were incubated in medium without acetate. These studies indicate that gentamicin stimulates active PAH transport and decreases PAH efflux in rat renal cortical slices. Both changes implicate an effect of gentamicin at the antiluminal membrane of proximal tubular cells. The finding of an increase in Vmax without a change in Km raises the possibility that gentamicin increases the amount or availability of carrier protein-mediating PAH transport.
研究了庆大霉素增强大鼠肾皮质切片对对氨基马尿酸（PAH）摄取的机制。在所有实验中，庆大霉素按硫酸庆大霉素100mg/kg体重每日给药，共2天；对照大鼠注射生理盐水。通过高效液相色谱法研究了庆大霉素对PAH代谢为对氨基苯甲酸（PABA）、乙酰-PABA和乙酰-PAH的影响。在含有PAH的培养基中孵育的注射庆大霉素或对照大鼠的肾切片中未检测到PAH的代谢产物。在含有8×10（-5）M 14C-PAH的培养基中孵育肾皮质切片2小时后，测量14C-PAH的流出量。对照切片的流出速率常数为0.080±0.003/分钟，庆大霉素处理的切片为0.059±0.003/分钟，P＜0.001。两组之间PAH的可扩散池没有显著差异，这支持了反对将PAH组织结合增加作为注射庆大霉素大鼠切片中PAH摄取增加的解释的观点。根据米氏动力学评估PAH的主动转运。对照切片的Vmax为0.93±0.08微摩尔/克/15分钟，庆大霉素处理的切片为1.37±0.10微摩尔/克/15分钟（P＜0.005）。表观反应速率常数（Km）没有差异；对照切片和庆大霉素处理的切片中的Km分别为0.25±0.03和0.29±0.04mM（P＜0.4）。与PAH相反，庆大霉素不改变有机碱N'-甲基烟酰胺的摄取；也不改变N'-甲基烟酰胺的流出速率常数或可扩散池。当将注射庆大霉素大鼠的切片在不含乙酸盐的培养基中孵育时，PAH摄取增加仍然明显。这些研究表明，庆大霉素刺激大鼠肾皮质切片中PAH的主动转运并降低PAH的流出。这两种变化都暗示庆大霉素对近端肾小管细胞的抗腔面膜有作用。Vmax增加而Km不变的发现增加了庆大霉素增加介导PAH转运的载体蛋白的量或可用性的可能性。
