A steep dependence of inward-rectifying potassium channels on cytosolic free calcium concentration increase evoked by hyperpolarization in guard cells
A steep dependence of inward-rectifying potassium channels on cytosolic free calcium concentration increase evoked by hyperpolarization in guard cells
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DOI：
10.1104/pp.119.1.277
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发表时间：
1999-01-01
期刊：
影响因子：
7.4
通讯作者：
Blatt, MR
中科院分区：
文献类型：
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作者：
Grabov, A;Blatt, MR
胞质游离[Ca2+]（[Ca2+](i)）升高导致向内纠偏的K+通道（i -K, i -in）失活是导致保护细胞溶质损失和气孔关闭的关键事件。然而，[Ca2+](i)对i - k， i -in的作用从未被量化，其起源也没有得到很好的理解。我们使用膜电压来控制[Ca2+](i), (a . Grabov和M.R. Blatt [1998] Proc . Acad Sci USA 95: 4778-4783)，同时在电压钳下记录i - k， i -in和Fura-2荧光比光度法记录[Ca2+](i)。i - k、i -in失活与[Ca2+](i)呈正相关，表明K-i为329 +/- 31 nM，每个通道有4个Ca2+离子协同结合。Ca2+通道拮抗剂Gd3+和calcicludine可促进i -K、i -in，两者均可抑制[Ca2+](i)的升高，但[Ca2+](i)的升高不受K+通道阻滞剂Cs+的影响。我们还发现，ryanodine是细胞内Ca2+通道的拮抗剂，介导Ca2+诱导的Ca2+释放，阻断了[Ca2+](i)的上升，并且Fura-2荧光的Mn2+猝灭表明膜超极化触发了细胞内储存的二价释放。这些和其他结果表明，在[Ca2+](i)控制i -K， i -in的高信号增益中，以及在膜电压反馈控制K+通道中离散Ca2+通量通路的作用。
Inactivation of inward-rectifying K+ channels (I-K,I-in) by a rise in cytosolic free [Ca2+] ([Ca2+](i)) is a key event leading to solute loss from guard cells and stomatal closure. However, [Ca2+](i) action on I-K,I-in has never been quantified, nor are its origins well understood. We used membrane voltage to manipulate [Ca2+](i), (A. Grabov and M.R. Blatt [1998] Proc Natl Acad Sci USA 95: 4778-4783) while recording I-K,I-in under a voltage clamp and [Ca2+](i) by Fura-2 fluorescence ratiophotometry. I-K,I-in inactivation correlated positively with [Ca2+](i) and indicated a K-i of 329 +/- 31 nM with cooperative binding of four Ca2+ ions per channel. I-K,I-in was promoted by the Ca2+ channel antagonists Gd3+ and calcicludine, both of which suppressed the [Ca2+](i) rise, but the [Ca2+](i) rise was unaffected by the K+ channel blocker Cs+. We also found that ryanodine, an antagonist of intracellular Ca2+ channels that mediate Ca2+-induced Ca2+ release, blocked the [Ca2+](i) rise, and Mn2+ quenching of Fura-2 fluorescence showed that membrane hyperpolarization triggered divalent release from intracellular stores. These and additional results point to a high signal gain in [Ca2+](i) control of I-K,I-in and to roles for discrete Ca2+ flux pathways in feedback control of the K+ channels by membrane voltage.