On the mechanism of spermine transport in liver mitochondria

• Published in: The Journal of biological chemistry Vol. 263; no. 36; pp. 19407 - 19411
• Main Authors: Toninello, A, Miotto, G, Siliprandi, D, Siliprandi, N, Garlid, K D
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25-12-1988; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Biological and medical sciences; Biological Transport - drug effects; Cell physiology; Fundamental and applied biological sciences. Psychology; Intracellular Membranes - physiology; Membrane and intracellular transports; Membrane Potentials; mitochondria; Mitochondria, Liver - metabolism; Molecular and cellular biology; Nigericin - pharmacology; Potassium - pharmacology; Quaternary Ammonium Compounds - metabolism; Rats; spermine; Spermine - metabolism; Valinomycin - pharmacology; Intracellular transport; Vertebrata; Mitochondria; Mammalia; Spermine; Rat; Liver; Rodentia; Membrane potential; Uptake; Internal membrane
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)77647-9

Spermine penetrates the mitochondrial matrix at significant rates which increase sharply and non-ohmically with membrane potential. In this respect, spermine uptake is qualitatively similar to that of other cations whose electrophoretic transport has been studied in mitochondria. At 200 mV and 1 mM spermine, the observed rate of spermine uptake was about 7 nmol x mg-1 x min-1, and the rate constant was about 8 times greater than that of tetraethylammonium cation. These rates are remarkably rapid considering that spermine is largely tetravalent at the pH of the experiment. The fluxes of spermine and tetraethylammonium are log-linear with membrane potential. The slope of the tetraethylammonium plot is consistent with leakage of this ion across a sharp Eyring barrier located in the middle of the membrane. The slope of the spermine plot is half that predicted by such a leak pathway, raising the possibility that spermine may cross the inner membrane by means of a channel. Whatever its mechanism of penetration, if comparable rates of uptake obtain in vivo and if spermine is not metabolized within the mitochondrial matrix, then a separate efflux mechanism would appear to be required to prevent unlimited spermine loading.