Schron C M, Knickelbein R G, Aronson P S, Della Puca J, Dobbins J W
Am J Physiol. 1985 Nov;249(5 Pt 1):G614-21. doi: 10.1152/ajpgi.1985.249.5.G614.
In brush-border membrane vesicles from rabbit ileum, we previously reported pH gradient-stimulated SO4 uptake and presented evidence that this represents carrier-mediated SO4-OH exchange. In the present study inhibitors of SO4-OH exchange (H-SO4 cotransport) were shown not to inhibit Na-SO4 cotransport, suggesting that these are two separate carrier-mediated transport mechanisms. While pH gradient-stimulated SO4 uptake was inhibited 87% by 0.1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, disodium salt (DIDS) and 79% by 1.0 mM furosemide, Na+-stimulated SO4 uptake was only inhibited 11 and 0%, respectively. K+ (20 mM), Cl (5 mM), and oxalate (0.25 mM) inhibited pH gradient-stimulated SO4 uptake (38-65%) but had no effect on Na+-stimulated SO4 uptake. Finally, at Na+ concentrations (10 mM) significantly less than that required for Na+-stimulated SO4 uptake (60-100 mM), external Na+ inhibited pH gradient-stimulated SO4 uptake, suggesting two independent effects of this cation. SO4 uptake was also inhibited by external K+ both in the presence and absence of a pH gradient. A Dixon plot of the DIDS-sensitive SO4 uptake under pH gradient conditions yielded a straight line, indicating a single site of interaction between external K+ and the SO4-OH carrier (apparent Ki = 7.2 mM). In contrast to the inhibition by external K+, internal K+ stimulated SO4 uptake. This effect was DIDS sensitive and not enhanced by valinomycin, suggesting an interaction of internal K+ with the SO4-OH exchanger independent of a K+-induced electrical potential. SO4 uptake and the effects of K+ were pH modulated with less SO4 uptake and less K+ effect at higher pH.(ABSTRACT TRUNCATED AT 250 WORDS)
在兔回肠的刷状缘膜囊泡中，我们之前报道过pH梯度刺激的硫酸根摄取，并提供证据表明这代表载体介导的硫酸根-氢氧根交换。在本研究中，硫酸根-氢氧根交换（氢-硫酸根共转运）的抑制剂未显示出抑制钠-硫酸根共转运，这表明它们是两种独立的载体介导的转运机制。虽然0.1 mM 4,4'-二异硫氰基芪-2,2'-二磺酸二钠盐（DIDS）使pH梯度刺激的硫酸根摄取抑制87%，1.0 mM速尿使其抑制79%，但钠刺激的硫酸根摄取仅分别被抑制11%和0%。钾离子（20 mM）、氯离子（5 mM）和草酸盐（0.25 mM）抑制pH梯度刺激的硫酸根摄取（38%-65%），但对钠刺激的硫酸根摄取无影响。最后，在钠离子浓度（10 mM）显著低于钠刺激的硫酸根摄取所需浓度（60-100 mM）时，细胞外钠离子抑制pH梯度刺激的硫酸根摄取，表明该阳离子有两种独立作用。无论有无pH梯度，细胞外钾离子均抑制硫酸根摄取。在pH梯度条件下，对DIDS敏感的硫酸根摄取进行狄克逊图分析得到一条直线，表明细胞外钾离子与硫酸根-氢氧根载体之间存在单一相互作用位点（表观抑制常数Ki = 7.2 mM）。与细胞外钾离子的抑制作用相反，细胞内钾离子刺激硫酸根摄取。这种作用对DIDS敏感，且不被缬氨霉素增强，表明细胞内钾离子与硫酸根-氢氧根交换体相互作用，与钾离子诱导的电势无关。硫酸根摄取及钾离子的作用受pH调节，在较高pH时硫酸根摄取减少，钾离子作用减弱。（摘要截短于250字）
