Binding of3H-desipramine to the neuronal noradrenaline carrier of rat phaeochromocytoma cells (PC-12 cells) |
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Authors: | H Bönisch R Harder |
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Institution: | (1) Institut für Pharmakologie und Toxikologie der Universität Würzburg, Versbacher-Strasse 9, D-8700 Würzburg, Federal Republic of Germany |
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Abstract: | Summary The specific (i.e., nisoxetine-sensitive) binding of3H-desipramine was studied in purified plasma membranes of PC-12 cells (rat phaeochromocytoma cells).3H-desipramine bound reversibly and with high affinity (K
D=4.5 nmol/l) to a single, non-interacting site (Hill coefficient=1.04); the maximal number of binding sites (B
max) was 19.6 pmol/mg protein.Like the uptake of noradrenaline (by uptake1), the binding of3H-desipramine was dependent on both sodium and chloride. The stimulation of binding by chloride and sodium was characterized by a Hill coefficient of about 1 and 2, respectively. Both, chloride and sodium, slowed the rate of dissociation of bound3H-desipramine. Increasing concentrations of sodium decreased theK
D of3H-desipramine binding without altering theB
max.The binding of3H-desipramine was inhibited by tricyclic antidepressants and other noradrenaline uptake blockers. There was a highly significant correlation between the potencies of a series of drugs for the inhibition of3H-desipramine binding and for the inhibition of3H-noradrenanne uptake into intact PC-12 cells. Both, binding of3H-desipramine and uptake of3H-noradrenaline, were stereoselectively inhibited by the enantiomers of cocaine and oxaprotiline. However, for most of the substrates of uptake1 the IC50 for inhibition of3H-desipramine binding was much higher than that for inhibition of3H-noradrenaline uptake. Nevertheless, noradrenaline competitively inhibited3H-desipramine binding and unmasked dissociation of bound3H-desipramine. Thus,3H-desipramine probably binds to the substrate recognition site.From theB
max of3H-desipramine binding to PC-12 membranes and from theV
max of3H-noradrenaline uptake into PC-12 cells, a duration of about 400 ms for the transport cycle for a single noradrenaline molecule was calculated. In addition, from theB
max the maximum number of3H-desipramine binding sites (carriers) for a single PC-12 cell was calculated to be 55,000.A part of this study was presented at the IUPAHR 9th International Congress of Pharmacology (Bönisch et al. 1984)This study was supported by the Deutsche Forschungsgemeinschaft (Bo 521 and SFB 176) |
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Keywords: | 3H-desipramine Neuronal noradrenaline carrier PC-12 cells |
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