Effects of Halothane on Transport of 5-Hydroxytryptamine by Platelet Membranes

Na+-dependent uptake of 5-HT (5-hydroxytryptamine) into plasma membrane vesicles derived from bovine blood platelets and ATP-dependent 5-HT uptake into storage vesicles in platelet lysates were measured. Na+-dependent uptake was temperature-dependent, inhibited by imipramine and exhibited Michaelis-Menten kinetics (apparent K(m), 0.12 ± 0.02 μM; V(max.) 559 ± 54 pmol/min per mg of protein. Halothane had no effect on Na+-dependent transport of 5-HT in plasma-membrane vesicles. ATP-dependent 5-HT transport into storage granules also exhibited Michaelis-Menten kinetics (apparent K(m) 0.34 ± 0.03 μM; V(max.) 34.3 ± 1.7 pmol/min per mg of protein) and was inhibited by noradrenaline (norepinephrine), but not by imipramine. Exposure of the granules to halothane resulted in a progressive decrease in V(max.). The results demonstrate a possible site for disruption of platelet function by anaesthetics