Reciprocal effects between spermine and Mg2+ on their movements across the mitochondrial membrane.
Mg(2+) competitively inhibits spermine transport in energized rat liver mitochondria (RLM) and exhibits a K(i) of 0.1mM on the initial rate and an I(50) of 0.6mM on total spermine accumulation after 20 min. Addition of 2mM Mg(2+) after spermine accumulation induces release of the polyamine. In view of the fact that spermine cycles across the inner membrane under physiological conditions, these results demonstrate that Mg(2+) inhibits spermine influx but does not affect the efflux pathway of the polyamine; the inhibitory effect occurs via an interaction with the specific site responsible for spermine transport. Instead, spermine inhibits Mg(2+) binding without affecting the rate of Mg(2+) transport, suggesting that both cations bind to the same site, which, however, is not used for Mg(2+) transport. Spermine also inhibits Mg(2+) efflux from RLM induced under conditions of the "low conductance state," a preliminary step preceding permeability transition pore opening.
Salvi
Mauro
M
Dipartimento di Chimica Biologica, Istituto di Neuroscienze del C.N.R., Universita' di Padova, Unita' per lo Studio delle Biomembrane, Via G. Colombo 3, 35121 Padova, Italy.
Toninello
Antonio
A
D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007425:Intracellular Membranes / Q000378:metabolism; D017136:Ion Transport; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D008564:Membrane Potentials; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013096:Spermine / Q000378:metabolism* / Q000493:pharmacokinetics
D013096:Spermine; D008274:Magnesium; D002118:Calcium