A difference in inward rectification and polyamine block and permeation between the Kir2.1 and Kir3.1/Kir3.4 K+ channels.
Inward rectification is caused by voltage-dependent block of the channel pore by intracellular Mg2+ and polyamines such as spermine. In the present study, we compared inward rectification in the Kir3.1/Kir3.4 channel, which underlies the cardiac current I(K,ACh), and the Kir2.1 channel, which underlies the cardiac current I(K,1). Sustained outward current at potentials positive to the K+ reversal potential was observed through Kir3.1/Kir3.4, but not Kir2.1, demonstrating that Kir3.1/Kir3.4 exhibits weaker inward rectification than Kir2.1. We show that Kir3.1/Kir3.4 is more sensitive to extracellular spermine block than Kir2.1, and that intracellular and extracellular polyamines can permeate Kir3.1/Kir3.4, but not Kir2.1, to a limited extent. We describe a simple kinetic model in which polyamines act as permeant blockers of Kir3.1/Kir3.4, but as relatively impermeant blockers of Kir2.1. The model shows the difference in sensitivity to extracellular spermine block, as well as the difference in the extent of inward rectification between the two channels. This suggests that Kir3.1/Kir3.4 exhibits weaker inward rectification than Kir2.1 because of the difference in the balance of polyamine block and permeation of the two channels.
Makary
Samy M Y
SM
Division of Cardiovascular and Endocrine Sciences, University of Manchester, Manchester Incubator Building, Manchester M13 9XX, UK.
Claydon
Tom W
TW
Enkvetchakul
Decha
D
Nichols
Colin G
CG
Boyett
Mark R
MR
D000818:Animals; D016466:CHO Cells; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003198:Computer Simulation; D006224:Cricetinae; D003412:Cricetulus; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D011073:Polyamines / Q000493:pharmacokinetics*; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*; D013096:Spermine / Q000494:pharmacology; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C489457:KCNJ2 protein, human; D011073:Polyamines; D024661:Potassium Channels, Inwardly Rectifying; D013096:Spermine