Extracellular K⁺ elevates outward currents through Kir2.1 channels by increasing single-channel conductance

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• 作者：Tai-An Liu^a ; Hsueh-Kai Chang^a ; Ru-Chi Shieh ; ^a ; ^{ruchi@ibms.sinica.edu.tw}
• 关键词：Inward-rectification ; Permeation ; Kinetics ; Excitability
• 刊名：Biochimica et Biophysica Acta (BBA)/Biomembranes
• 出版年：2011
• 出版时间：June 2011
• 年：2011
• 卷：1808
• 期：6
• 页码：1772-1778
• 全文大小：1097 K

文摘

Outward currents through inward rectifier K⁺ channels (Kir) play a pivotal role in determining resting membrane potential and in controlling excitability in many cell types. Thus, the regulation of outward Kir current (I_K1) is important for appropriate physiological functions. It is known that outward I_K1 increases with increasing extracellular K⁺ concentration ([K⁺]_o), but the underlying mechanism is not fully understood. A “K⁺-activation of K⁺-channel” hypothesis and a “blocking-particle” model have been proposed to explain the [K⁺]_o-dependence of outward I_K1. Yet, these mechanisms have not been examined at the single-channel level. In the present study, we explored the mechanisms that determine the amplitudes of outward I_K1 at constant driving forces [membrane potential (V_m) minus reversal potential (E_K)]. We found that increases in [K⁺]_o elevated the single-channel current to the same extent as macroscopic I_K1 but did not affect the channel open probability at a constant driving force. In addition, spermine-binding kinetics remained unchanged when [K⁺]_o ranged from 1 to 150 mM at a constant driving force. We suggest the regulation of K⁺ permeation by [K⁺]_o as a new mechanism for the [K⁺]_o-dependence of outward I_K1.