Sulfonylurea binding to a low-affinity site inhibits the Na/K-ATPase and the KATP channel in insulin-secreting cells.
Sulfonylurea binding to a low-affinity site inhibits the Na/K-ATPase and the KATP channel in insulin-secreting cells.
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DOI：
10.1085/jgp.107.2.231
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发表时间：
1996-02
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影响因子：
--
通讯作者：
Levin SR
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文献类型：
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作者：
Ribalet B;Mirell CJ;Johnson DG;Levin SR
我们使用仓鼠胰岛素瘤细胞（HIT），一种胰岛素分泌肿瘤细胞系，研究磺脲格列本脲对Na/K-ATP酶和ATP敏感的K通道（K(ATP)）的调节。通过高低结合亲和力常数（K(d)分别= 0.96和91 nM）证明，在含11 mM葡萄糖的RPMI中培养的细胞膜蛋白至少有两个格列本脲受体群体。在这些细胞中，K（ATP）通道活性被低浓度格列本脲阻断，IC(50) = 5.4 nM。在12.5 nM格列本脲时，抑制作用发展缓慢，tau = 380 s，导致通道活性降低75%。然而，在较高的浓度下，抑制发生的速度很快，在100 nM下tau = 42 s，并且几乎完全。酶学和电生理测量的Na/K- atp酶活性也被格列本脲抑制，但需要更高的浓度，IC(50) = 20-40 nM。抑制发生迅速，50 nM时tau = 30 s，最大时活性降低40%。相比之下，在添加25 mM葡萄糖的RPMI中培养的细胞表现出低亲和力的单一受体群体结合格列本脲，K(d)= 68 nM。在这些细胞中，磺酰脲对Na/K-ATP酶的抑制作用与在11 mM葡萄糖中培养的细胞相似，但K（ATP）通道的抑制作用明显改变。抑制作用仅在高浓度格列本脲和快速作用下发生；在100 nM处观察到最大抑制作用。基于这些数据，我们提出格列本脲与高亲和力位点的结合主要影响K（ATP）通道活性，而与低亲和力位点的相互作用抑制Na/K-ATP酶和K（ATP）通道活性。后一种观察结果表明Na/K-ATP酶和K（ATP）通道之间可能存在功能相互作用。
We have used hamster insulinoma tumor (HIT) cells, an insulin-secreting tumor cell line, to investigate modulation of the Na/K-ATPase and of the ATP-sensitive K channel (K(ATP)) by the sulfonylurea glyburide. Membrane proteins from cells cultured in RPMI with 11 mM glucose have at least two glyburide receptor populations, as evidenced by high and low binding affinity constants, (K(d) = 0.96 and 91 nM, respectively). In these cells K(ATP) channel activity was blocked by low glyburide concentrations, IC(50) = 5.4 nM. At 12.5 nM glyburide the inhibition developed slowly, tau = 380 s, and caused reduction of channel activity by 75 percent. At higher concentrations, however, inhibition occurred at a fast rate, tau = 42 s at 100 nM, and was almost complete. Na/K- ATPase activity measured enzymatically and electrophysiologically was also suppressed by glyburide, but higher concentrations were needed, IC(50) = 20-40 nM. Inhibition occurred rapidly, tau = 30 s at 50 nM, when maximum, activity was reduced by 40 percent. By contrast, cells cultured in RPMI supplemented with 25 mM glucose exhibit a single receptor population binding glyburide with low affinity, K(d)= 68 nM. In these cells inhibition of the Na/K-ATPase by the sulfonylurea was similar to that observed in cells cultured in 11 mM glucose, but K(ATP) channel inhibition was markedly altered. Inhibition occurred only at high concentrations of glyburide and at a fast rate; maximum inhibition was observed at 100 nM. Based on these data, we propose that glyburide binding to the high affinity site affects primarily K(ATP) channel activity, while interaction with the low affinity site inhibits both Na/K-ATPase and K(ATP) channel activities. The latter observation suggests possible functional interactions between the Na/K-ATPase and the K(ATP) channel.