Block of the Kir2.1 Channel Pore by Alkylamine Analogues of Endogenous Polyamines

Abstract

Inward rectification induced by mono- and diaminoalkane application to inside-out membrane patches was studied in Kir2.1 (IRK1) channels expressed in Xenopus oocytes. Both monoamines and diamines block Kir2.1 channels, with potency increasing as the alkyl chain length increases (from 2 to 12 methylene groups), indicating a strong hydrophobic interaction with the blocking site. For diamines, but not monoamines, increasing the alkyl chain also increases the steepness of the voltage dependence, at any concentration, from a limiting minimal value of ∼1.5 (n = 2 methylene groups) to ∼4 (n = 10 methylene groups). These observations lead us to hypothesize that monoamines and diamines block inward rectifier K+ channels by entering deeply into a long, narrow pore, displacing K+ ions to the outside of the membrane, with this displacement of K+ ions contributing to “extra” charge movement. All monoamines are proposed to lie with the “head” amine at a fixed position in the pore, determined by electrostatic interaction, so that zδ is independent of monoamine alkyl chain length. The head amine of diamines is proposed to lie progressively further into the pore as alkyl chain length increases, thus displacing more K+ ions to the outside, resulting in charge movement (zδ) increasing with the increase in alkyl chain length.

Mechanism of Rectification in Inward-Rectifier K+ Channels

“…Indeed, Z obs increases with chain length in apparent steps of approximately one, reaching a plateau of approximately five at about that of bis-C8 (filled circles in Fig. 6 B; compare Pearson and Nichols, 1998;Guo and Lu, 2000a). (The lower plateau valence for block of the D172N mutant channel (filled triangles) probably reflects reduced K ϩ occupancy.)…”

“…In an intuitively plausible model of pore block by mono-amines (Pearson and Nichols, 1998), the sole amine always binds at the same site in the pore while the alkyl tails of varying length point to the intracellular solution. If this were the case, the rate constant for channel block by a given mono-amine should, from statistical considerations, be twofold smaller than that by the corresponding bis-amine, and the voltage dependence of channel block should be unaffected by chain length.…”

“…Because of this precedent and the observation that polyamine block is also affected by the external K ϩ concentration (e.g., Lopatin and Nichols, 1996), the possibility should be kept in mind that the voltage dependence of channel block by polyamines results (at least in part) from the movement, across the electrical field, of multiple K ϩ ions residing in the long channel pore. Pearson and Nichols (1998) examined IRK1 block by a series of bis-and mono-alkyl-amines (bis-amines and mono-amines) of varying length, a type of approach pioneered with bis-quaternary ammonium by Miller (1982) in a study of sarcoplasmic reticulum K ϩ channels. Finding that the apparent affinity for bis-amines increases with alkyl chain length, they concluded that hydrophobic interactions contribute to the overall binding energy.…”

Restorative role of Deprenyl on Mitochondrial function of aging rat cerebellum

“…The interaction of the monovalent cationic drug with critical amino acid residues present in the pore forming structures can be responsible for the observed inhibition. In this regard, Deprenyl can interact with the ring of aromatic residues by means of cation π interactions [33] or with carboxylate ions by means of weak electrostatic interactions [34].…”

Polyamine Permeation and Rectification of Kir4.1 Channels

“…[21][22][23] Briefly, COSm6 cells were transfected with pCMV-Kir4.1 (with insertion of Kir2.1 trafficking sequence 24 "NSFCYENEVALT" immediately after residue P272, to increase expression density). Patch-clamp experiments were made at room temperature, in a chamber that allowed the solution bathing the exposed surface of the isolated patch to be changed rapidly.…”