Net taurine transport and its inhibition by a taurine antagonist.
P2-fractions were isolated from rat brain, and used to study net taurine transport. The fractions were incubated in increasing concentrations of [3H]taurine and the intraterminal concentration measured by liquid scintillation and amino acid analysis. The membrane potential of the isolated fractions was estimated using 86Rb+ as a marker for intracellular K+. Taurine was synthesized in the P2-fraction when incubated in taurine free medium. At external taurine concentrations below 370 microM a significant amount of the endogenous taurine was released to the incubation medium. Net taurine uptake into the P2-fraction was achieved at external taurine concentrations exceeding 370 microM. The taurine antagonist 6-aminomethyl-3-methyl-4H, 1, 2, 4-benzothiadiazine-1, 1-dioxide (TAG) competitively inhibited taurine and [3H]taurine transport into the P2-fraction. As the external concentration of taurine was increased, the accumulation of 86Rb+ into the P2-fraction was facilitated. This indicated an increasing hyperpolarization of the neuronal membrane as taurine transport shifted from release towards uptake. TAG reduced the hyperpolarization that paralleled taurine accumulation, in a dose dependent manner. Our results indicate that relatively low transmembranal gradients of taurine may be maintained by an electrogenic taurine transporter having a large transport capacity. Such a transporter may well serve the needs of osmotic regulation, i.e. to transport large amounts of taurine in any direction across the neuronal membrane.
Lewin
L
L
Department of Zoophysiology, University of Umeå, Sweden.
Rassin
D K
DK
Sellström
A
A
D000818:Animals; D001581:Benzothiadiazines / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D007700:Kinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012413:Rubidium / Q000378:metabolism; D012414:Rubidium Radioisotopes; D012588:Scintillation Counting; D013654:Taurine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014316:Tritium
D001581:Benzothiadiazines; D012414:Rubidium Radioisotopes; D014316:Tritium; D013654:Taurine; C032946:6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine 1,1-dioxide; D012413:Rubidium