The relationship between sodium and high-affinity taurine uptake in hypothalamic crude P2 synaptosomal preparations.
Two uptake systems for taurine transport in a rat hypothalamic crude synaptosomal preparation were identified. The true transport constants were, for the high-affinity uptake system, Km = 240 microM and V (maximum velocity) = 400 nmol/g protein/min, and for the low-affinity uptake system, Km = 5290 microM and V = 1640 nmol/g protein/min. The initial velocity of high-affinity taurine uptake by the crude synaptosomal preparation was studied as a function of sodium and taurine concentration. Hill plots were constructed from these data. The requirement of high-affinity taurine uptake on a sodium gradient was examined by utilizing monensin, and the metabolic poisons, 2,4-dinitrophenol and ouabain. The major findings are as follows: 1) One sodium ion is co-transported with each taurine molecule; 2) the high-affinity uptake process is driven by the sodium concentration gradient across the membrane; 3) sodium increases the maximal velocity rather than the affinity of the high-affinity taurine carrier for the taurine molecule; 4) one taurine molecule is transported per carrier for both the high- and low-affinity taurine uptake systems; and 5) high-affinity taurine uptake is an energy-dependent process.
D019297:2,4-Dinitrophenol; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D004140:Dinitrophenols / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D007700:Kinetics; D008985:Monensin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*
D004140:Dinitrophenols; D013654:Taurine; D010042:Ouabain; D008985:Monensin; D012964:Sodium; D019297:2,4-Dinitrophenol