Molecular and Functional Characteristics of Glycerol Transporter in HCT-15 Cell Model

为了阐明甘油转运体的分子和功能特征，我们在HCT-15细胞中对依赖Na+的转运体进行了研究，特别是考察了1)丁酸处理诱导细胞分化和2)几种结构类似甘油的化合物对甘油摄取的影响。丁酸处理使甘油最大转运率增加约5倍，但不显著改变米氏常数(亲和力)。丁酸处理的细胞对甘油的摄取高度依赖于Na+，并被一些结构类似的化合物特异性地抑制，这表明对Na+依赖的甘油转运蛋白的诱导。此外，这种诱导几乎完全被基因转录抑制剂放线菌素D和蛋白质合成抑制剂放线菌亚胺所抑制。所有这些发现都为存在甘油的特定转运蛋白提供了证据。在SIV…中更多的外在化合物被测试其对甘油摄取的抑制作用，单乙酸单丁酯被发现是最有效的抑制物，它们是甘油的酯类衍生物。因为它们竞争性地抑制甘油的摄取，它们可能是甘油转运蛋白的底物。这表明药物的甘油酯衍生物可能通过转运体输送。有趣的是，1，2-丙二醇具有竞争抑制的对映体选择性特征，其中S-(+)-对映体比R-(-)-对映体更受转运体的青睐。所有这些特征也是由特定转运蛋白介导的转运特征，为存在这种特定的甘油转运蛋白提供了额外的证据。因此，我们可以获得几条证据，证明HCT-15细胞中存在依赖钠离子的甘油转运蛋白。这将有助于鉴定它并阐明它的运输机制和生理作用。较少

To clarify the molecular and functional characteristics of glycerol transporters, we conducted studies on a Na^+-dependent one in HCT-15 cells, particularly examining the effects on glycerol uptake of 1) cell differentiation induced by butyrate treatment and 2) several compounds structurally analogous to glycerol.Butyrate treatment brought about an approximately 5-fold increase in the maximum glycerol transport rate, without altering the Michaelis constant (affinity) significantly. Glycerol uptake in butyrate-treated cells was highly Na^+-dependent and specifically inhibited by some structurally analogous compounds as it was in untreated cells, indicating an induction of the Na^+-dependent glycerol transporter. Furthermore, this induction was almost completely suppressed by actinomycin D, an inhibitor of gene transcription, and cycloheximide, an inhibitor of protein synthesis. All these findings provide evidences for the presence of a specific transporter protein for glycerol.Among sev … More eral compounds tested for their inhibitory effects on glycerol uptake, monoacetin and monobutyrin, which are ester type of glycerol derivatives, were found to be the most potent inhibitors. Because they inhibited glycerol uptake competitively, they may possibly be substrates of the glycerol transporter. This would suggest that glycerol ester derivatives of drugs might be delivered via the transporter. Interestingly, enantioselective characteristic was found for competitive inhibition, though relatively weak, by 1, 2-propanediol, where the S-(+)-enantiomer is favored by the transporter than the R-(-)-enantiomer. All these features are also characteristic of transport mediated by a specific transporter protein, providing additional evidences for the presence of such a specific transporter protein for glycerol.Thus, we could obtain several lines of evidences for the presence of a Na^+-dependent glycerol transporter in HCT-15 cells. This would help in identifying it and elucidating its transport mechanism and physiological role. Less