Lysosomal Sulfate Transport is Stimulated by Trivalent Cations

三價陽離子會增強溶小體膜上的硫酸根運輸

葉思芳(Hsu-Fang Chou) ； Peter Koetters ； Merry Passage ； Kathy Chen ； Adam J. Jonas

《慈濟醫學雜誌》 17卷6期 (2005/12) Pp. 397-404

https://doi.org/10.6440/TZUCMJ.200512.0397

摘要

目的：本實驗探討三價陽離子對老鼠肝細胞中溶小體膜上的硫酸根運輸系統的影響。材料與方法：溶小體由老鼠的肝臟分離、純化。硫酸根的運送速率是利用放射性元素標定的硫酸根[35S]-Na2SO4及過濾的方法測量。結果：三價陽離子，例如鑭(lanthanum)會促進溶小體膜上硫酸根的運送，而二價陽離子則不影響。鑭在100 μM的濃度會增加硫酸根運送速率達4-8倍，可是對葡萄糖運送速率則無影響。由鑭所增加的硫酸根運輸也是受培養時間，溫度，酸鹼度的調控，且具飽和動力(saturation kinetics)(Km=90 μM)，也被DIDS抑制。鑭對硫酸根運輸力的促進以在pH 5.0，且兩者都在膜的同一邊時最強。鑭並不影響硫酸根的countertransport。鑭所增加的硫酸根運輸也會受CCCP(protonphore)的抑制。結論：鑭可能會與溶小體膜上的硫酸根運輸蛋白相作用，或是與溶小體膜作用使得膜內外氫離子梯度(proton gradient)更有效的來幫助硫酸根運送。

關鍵字

溶小體膜硫酸根運輸系統 ； 三價陽離子 ； 鑭lanthanum

並列摘要

Objective: To study the regulatory roles of multivalent cations on lysosomal sulfate transport. Materials and Methods: Lysosomes were isolated and purified from Sprague-Dawley rat liver. Sulfate transport was measured using a filtration system and radioactive-labeled substrates. Results: Sulfate uptake by lysosomal membrane vesicles and intact lysosomes was markedly increased in the presence of trivalent cations such as lanthanum but was relatively unaffected by divalent cations such as calcium. The order of stimulatory potency of tested trivalent cations on sulfate transport was LaCl3＞AlCl3＞FeCl3＞CrCl3. Uptake of 100 μM sulfate increased between 4 and 8-fold in the presence of 100 μM lanthanum (K1/2=42 μM lanthanum) while uptake of glucose remained largely unchanged. Similar to previously reported characteristics of lysosomal sulfate transport, lanthanum-stimulated sulfate uptake was time dependent, pH-dependent, temperature-dependent, exhibited saturation kinetics (Km=90 μM) and was sensitive to inhibition by 4,4”-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). Lanthanum stimulation of sulfate at pH 5.0 was greatest when sulfate and lanthanum were on the same side of the membrane. This was not the case for sulfate countertransport at pH 7.0 which was unaffected by the presence of lanthanum in the extra-vesicular buffer, consistent with an already maximal rate of transport. Lanthanum-stimulated sulfate uptake was inhibited by the protonophore, CCCP. Conclusion: It appears that lanthanum and other trivalent cations interact with the lysosomal membrane sulfate transporter to allow for enhanced function possibly by substituting for the effects of hydrogen ions.

並列關鍵字

lysosomal sulfate transport ； trivalent cations ； lanthanum