IN-VIVO AND IN-VITRO STUDIES OF THE INHIBITION OF THE CHANNEL ACTIVITY OF COLICINS BY GADOLINIUM

The primary effects of the ionophoric colicins A, E1 and B on Escheric hia coli cells include triggering an efflux of cytoplasmic potassium, and a decrease of internal ATP as consequences of the opening of ionic channels in the cytoplasmic membrane. We report that micromolar conce ntrations of gadolinium and other members of the lanthanide family inh ibited the efflux of potassium and the ATP decrease and that the cells recovered both ATP and potassium within a few minutes. Gadolinium, in the same concentration range also efficiently inhibited the channel a ctivity of colicins A, E1, B and of the isolated channel-forming domai n of colicin A in planar lipid bilayers. Colicin N was much less sensi tive to the trivalent ion in planar lipid bilayers, consistent with th e lack of effect of gadolinium on this colicin in vivo. Our data sugge st that lanthanide ions act by direct binding to the colicin molecule and that this binding affects both its single-channel conductance and gating behaviour.