A structural determinant of differential sensitivity of cloned inward rectifier K⁺ channels to intracellular spermine

Abstract

Large subtype-specific differences in the sensitivity of cloned inward-rectifier K' channels of the IRKl, BIRlO and ROMKl subtype to being blocked by intracellular spermine (SPM) are described. It is shown, by site-directed mutagenesis, that the four orders of magnitude larger SPM sensitivity of BIRlO channels compared to ROMKl channels may be explained by a difference in a single amino acid in the putative transmembrane segment TMII. This residue, a negatively charged glutamate in BIRlO, is homologous to the residue in IRK1 and ROMKl which has previously heen shown to change gating properties and Me sensitivity. Differential block by physiological SPM concentrations is suggested as a major functional difference between subtypes of inward-rectifier K' channels.

Different modes of inhibition by adamantane amine derivatives and natural polyamines of the functionally reconstituted influenza virus M2 proton channel protein.

“…The established antiviral drugs amantadine and rimantadine were compared with rimantadine derivatives and cyclic amines on the one hand and with spermine, spermidine and putrescine on the other. These ubiquitous and abundant polyamines, which serve a number of diverse physiological functions, have recently been shown to gate potassium channels (Fakler et al, 1994 ;Ficker et al, 1994 ;Lopatin et al, 1994) and we demonstrate here that they also inhibit proton translocation by the influenza virus M2 protein.…”

An Inwardly Rectifying Potassium Channel in Apical Membrane of Calu-3 Cells

“…These results are in sharp contrast to the ATP dependence of Kir2.1 (35) and Kir4.1 (31). The Kir6.x subfamily of channels is modulated by ATP in a dual fashion, with activity sustained at low cytoplasmic concentrations via a phosphorylation-dependent step (36,37), but inhibited at higher concentrations via non-hydrolytic binding (36,38,39).…”

C-terminus determinants for Mg2+ and polyamine block of the inward rectifier K+ channel IRK1.

“…The ROMKI N171D mutant increased Mg;+ affinity by -10-fold (Lu and MacKinnon, 1994;Wible et al, 1994) and SPD affinity by 104-fold Lopatin et al, 1994), whereas the IRKI D172N mutation only accounts for a 20-fold difference in SPD affinity, with no change in Mg;' blocking rates . Also in a recently cloned IRK from the rat brain, BIRlO, the substitution of the corresponding negatively charged M2 position with an asparagine (mutation BIRlO E158N) caused a loss by as much as five orders of magnitude of sensitivity to SPM (Fakler et al, 1994 virtually instantaneous and no apparent inactivation of the outward current could be detected . In IRKI E224G, the exit from the blocked channel (OFF rate) of Mg2, which is virtually instantaneous in IRKI, is greatly slowed, leading to time-dependent macroscopic current activation upon hyperpolarization ( Figure 8A).…”

“…Inward rectification in IRKs has been attributed to both fast blockade of the pore by internal Mg2+ and/or a slow 'intrinsic' gating process (Matsuda et al, 1987;Vandenberg, 1987;Ishihara et al, 1989;Silver and DeCoursey, 1990). In cloned IRKs, intrinsic gating has recently been shown to depend on pore blockade by cytoplasmic polyamines (PAs), particularly spermidine (SPD) and spermine (SPM) (Fakler et al, 1994(Fakler et al, , 1995Ficker et al, 1994;Lopatin et al, 1994).…”