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Effects of N‐ethylmaleimide on 5‐hydroxytryptamine transport and sodium content in rabbit platelets
Author(s) -
Wölfel R.,
Halbrügge T.,
Graefe K.H.
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb12593.x
Subject(s) - n ethylmaleimide , ouabain , chemistry , platelet , sodium , imipramine , medicine , endocrinology , intracellular , potency , membrane transport , biophysics , biochemistry , membrane , in vitro , biology , alternative medicine , organic chemistry , pathology
1 The present study analysed the mechanism underlying the inhibitory action of N‐ethylmaleimide (NE m ) on the 5‐hydroxytryptamine (5‐HT) uptake by blood platelets. 2 Rabbit platelets suspended in protein‐free buffer were first preincubated for 45 min in the absence and presence of NEM (20 to 160 μ m ) or ouabain (0.5‐2.0 μ m ) and then either analysed for their Na + and K + content or incubated (15 s) with various concentrations of [ 3 H]‐5‐HT (0.13‐4.03 μ m ) to determine K m and V max for 5‐HT uptake. 3 Both NEM and ouabain produced concentration‐dependent decreases in V max with IC 50 values of 52 and 0.58 μ m , respectively. Neither drug changed K m significantly. 4 Both NEM and ouabain increased the Na + and decreased the K + content of platelets in a concentration‐dependent manner. 5 There was a linear correlation between V max (expressed in % of control) and the reciprocal cellular Na + content, with the results for both drugs falling onto one and the same regression line (r = 0.992; n = 8). This regression showed that an increase in Na + content by 69% sufficed to reduce V max by 50%. 6 At concentrations that reduced 5‐HT uptake by about 60%, neither NEM nor ouabain altered the potency of imipramine for inhibition of 5‐HT uptake. 7 Hence, NEM inhibits 5‐HT transport by inhibiting the Na + /K + ‐ATPase and not by a direct interaction with the 5‐HT carrier. The consequential increase in the intracellular Na + concentration reduces the transmembrane Na + gradient and, therefore, hinders 5‐HT inward transport. This action of the drug does not affect the ability of the carrier to bind 5‐HT or imipramine.