The extracellular K concentration dependence of outward currents through Kir2.1 channels is regulated by extracellular Na and Ca2 Article uri icon

abstract

  • It has been known for more than three decades that outward Kir currents (IK1) increase with increasing extracellular K concentration ([K ]o). Although this increase in I K1 can have significant impacts under pathophysiological cardiac conditions, where [K ]o can be as high as 18 mM and thus predispose the heart to re-entrant ventricular arrhythmias, the underlying mechanism has remained unclear. Here, we show that the steep [K ]o dependence of Kir2.1-mediated outward IK1 was due to [K ]o-dependent inhibition of outward I K1 by extracellular Na and Ca2 . This could be accounted for by Na /Ca2 inhibition of IK1 through screening of local negative surface charges. Consistent with this, extracellular Na and Ca2 reduced the outward single-channel current and did not increase open-state noise or decrease the mean open time. In addition, neutralizing negative surface charges with a carboxylate esterifying agent inhibited outward IK1 in a similar [K ]o-dependent manner as Na /Ca2 . Site-directed mutagenesis studies identified Asp114 and Glu 153 as the source of surface charges. Reducing K activation and surface electrostatic effects in an R148Y mutant mimicked the action of extracellular Na and Ca2 , suggesting that in addition to exerting a surface electrostatic effect, Na and Ca 2 might inhibit outward IK1 by inhibiting K activation. This study identified interactions of K with Na and Ca2 that are important for the [K ] o dependence of Kir2.1-mediated outward IK1. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.
  • It has been known for more than three decades that outward Kir currents (IK1) increase with increasing extracellular K%2b concentration ([K%2b]o). Although this increase in I K1 can have significant impacts under pathophysiological cardiac conditions, where [K%2b]o can be as high as 18 mM and thus predispose the heart to re-entrant ventricular arrhythmias, the underlying mechanism has remained unclear. Here, we show that the steep [K %2b]o dependence of Kir2.1-mediated outward IK1 was due to [K%2b]o-dependent inhibition of outward I K1 by extracellular Na%2b and Ca2%2b. This could be accounted for by Na%2b/Ca2%2b inhibition of IK1 through screening of local negative surface charges. Consistent with this, extracellular Na%2b and Ca2%2b reduced the outward single-channel current and did not increase open-state noise or decrease the mean open time. In addition, neutralizing negative surface charges with a carboxylate esterifying agent inhibited outward IK1 in a similar [K%2b]o-dependent manner as Na%2b/Ca2%2b. Site-directed mutagenesis studies identified Asp114 and Glu 153 as the source of surface charges. Reducing K%2b activation and surface electrostatic effects in an R148Y mutant mimicked the action of extracellular Na%2b and Ca2%2b, suggesting that in addition to exerting a surface electrostatic effect, Na%2b and Ca 2%2b might inhibit outward IK1 by inhibiting K%2b activation. This study identified interactions of K%2b with Na %2b and Ca2%2b that are important for the [K%2b] o dependence of Kir2.1-mediated outward IK1. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

publication date

  • 2010-01-01