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Serotonin (5-HT) uptake by bovine pulmonary artery endothelial cells in culture was measured at 5-HT concentrations of 1.5 X 10(-8) to 10(-3) M. The uptake increased linearly at concentrations of 10(-5) to 10(-3) M 5-HT, and the slope for uptake was 1.276 X 10(6) pmol 5-HT X 10(6) cells-1 X 30 min-1 X M concentration-1. The slope for uptake at 5-HT concentrations less than 10(-7) M was 7.10 X 10(6) pmol X 10(6) cells-1 X 30 min-1 X M concentration-1. With subtraction of the slope for linear uptake obtained at high concentrations of 5-HT from total uptake of 5-HT, a curve showing saturable uptake at concentrations greater than 10(-6) to 10(-5) M was obtained. Lineweaver-Burk analysis of the data yielded a saturated value of high-affinity transport of 6.25 pmol X 10(6) cells-1 X 30 min-1 and a Km of 10(-6) M. At 5-HT concentrations of 1.5 X 10(-8) to 5 X 10(-7) M, uptake was inhibited 75-80% by exposure to 4 degrees C or by absence of sodium in the medium; absence of sodium did not affect uptake at 5-HT concentrations greater than 10(-5) M, and 4 degrees C was less effective in inhibiting uptake at high 5-HT concentrations. Imipramine markedly inhibited uptake at low, but not at high, 5-HT concentrations. Ouabain only partially inhibited 5-HT uptake, but inhibition was more pronounced at low 5-HT concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Lee et al. (Thu,) studied this question.