An unusual form of the association binding kinetics of N-[ [H-3] methylscopolamine to the split muscarinic M-2trunk/M-2tail receptor

作者：Novi F; Scarselli M; Corsini GU; Maggio R^*

来源：Journal of Pharmacology and Experimental Therapeutics, 2003, 305(2): 786-795.

DOI：10.1124/jpet.102.045393

The muscarinic M-2 receptor was split at the third cytoplasmic loop into two fragments: the one containing the first five transmembrane regions and the N-terminal part of the third cytoplasmic loop was named M-2trunk, while the other, which contained the last two transmembrane regions and the C-terminal part of the third cytoplasmic loop, was named M-2tail. As seen in many other G protein-coupled receptors, when these two fragments were transfected together in COS-7 cells they rescued the pharmacological profile and the functional activity of the wild-type M-2 receptor. Conversely, N-[H-3] methylscopolamine ([H-3] NMS) association binding experiments showed a substantial difference between the wild-type M-2 and the split M-2trunk/ M-2tail receptors. The progression of the association binding kinetic of the M-2trunk/M-2tail receptor was strictly dependent upon the amount of the fragment DNA transfected. When the amount of transfected DNA was 4 mug/plate and the B-max of [H-3] NMS at equilibrium was around 200 fmol/mg protein the form of the association was that of classical saturation, but when the amount of transfected DNA was lower the [H-3] NMS association reached a maximum binding point and then declined to a lower equilibrium binding level. The form of the association was temperature-dependent: as the temperature was lowered, the maximum binding point tended to be higher. We suggest that this peculiar form of the [H-3] NMS association binding to the muscarinic M-2trunk/M-2tail receptor is attributable to a less stable interaction between the trunk and the tail fragments of the split receptor.

• 出版日期2003-5