N- and C-terminal substance P fragments: differential effects on striatal [3H]substance P binding and NK1 receptor internalization.
N- and C-terminal substance P (SP) fragments increase striatal dopamine outflow at nanomolar concentrations. This contrasts with their low affinity for NK1 receptors. To explore this discrepancy, we investigated the interaction of SP and SP fragments with NK1 sites in fresh striatal slices, the same model used in the functional studies on dopamine outflow. [3H]SP bound specifically to one site (Kd = 6.6 +/- 0.9 nM; Bmax = 12.6 +/- 0.7 fmol/mg protein). [3H]SP binding was displaced by SP (IC50 = 11.8 nM), but not by SP(1-7) or SP(5-11), up to 10 microM. In contrast, 10 nM SP(1-7) or SP(5-11) induced significant internalization of the NK1 receptor, similar to that induced by SP. We suggest that SP fragments have high affinity for an NK1 receptor conformer which is different from that labelled by [3H]SP.
Michael-Titus
A T
AT
Division of Biomedical Sciences, Queen Mary and Westfield College, London, UK.
Blackburn
D
D
Connolly
Y
Y
Priestley
J V
JV
Whelpton
R
R
D000704:Analysis of Variance; D000818:Animals; D003342:Corpus Striatum / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D013373:Substance P / Q000737:chemistry / Q000378:metabolism*
D010446:Peptide Fragments; D018040:Receptors, Neurokinin-1; D013373:Substance P