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High selectivity of the i f channel to Na+ and K+ in rabbit isolated sinoatrial node cells

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Abstract

The ionic selectivity of the hyperpolarizationactivated inward current (i f) channel to monovalent cations was investigated in single isolated sinoatrial node cells of the rabbit using the whole-cell patch-clamp technique. With a 140 mM K+ pipette, replacement of 90% external Na+ by Li+ caused a −24.5 mV shift of the fully activated current/voltage I/V curve without a significant decrease of the slope conductance. With a 140 mM Cs+ pipette, the i f current decreased almost proportionally to the decrease in external [Na+]o as Li+ was substituted. These responses are practically the same as those observed with N-methyl glucamine (NMG+) substitution, suggesting that the relative permeability of Li+ compared with Na+ for the i f channel is as low as that of NMG+. When Cs+ or Rb+ was substituted for internal K+, the fully activated I/V relationship for i f showed strong inward rectification with a positive reversal potential, indicating low permeability of the i f channel for Cs+ and Rb+. These results show that the i f channel is highly selective for Na+ and K+ and will not pass the similar ions Li+ and Rb+. Such a high degree of selectivity is unique and may imply that the structure of the i f channel differs greatly from that of other Na+ and K+ conducting channels.

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Ho, W.K., Brown, H.F. & Noble, D. High selectivity of the i f channel to Na+ and K+ in rabbit isolated sinoatrial node cells. Pflugers Arch. 426, 68–74 (1994). https://doi.org/10.1007/BF00374672

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  • DOI: https://doi.org/10.1007/BF00374672

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