Pre‐exposure of the urotensin II receptor to urotensin II or urotensin II‐related peptide differentially reduces the response to subsequent additions (1066.8)

The Urotensin II receptor (UIIR) is a G protein‐coupled receptor which is activated by urotensin II (UII) and urotensin‐related peptide (URP). Studies show equivalent K d values and a similar EC 50 in Ca 2+ assays in vitro . The co‐expression of the peptides, spatially and temporally, in vivo leads us to hypothesize that the ligands mediate different post‐activation events. Ca 2+ mobilization was used to monitor receptor activation. CHO‐rUIIR cells pre‐treated with 1pM UII have a 40% reduction in response to a second addition of 10nM UII. The same experiment was carried out with equimolar URP; no significant decrease was seen. The same phenomenon was seen when cells were pre‐treated for 6 or 19 minutes, washed, and a second addition added one hour later. UII and URP have identical cyclic regions, but UII has an additional short n‐terminal tail containing a charged residue. The Ca 2+ assay was repeated using peptide truncations, and these truncations resulted in differential desensitization. Desensitization mechanisms may lead to proliferative pathways. Therefore, cells were treated with UII or URP overnight. UII dose‐dependently increased MTS reduction (130%; MTS assay) compared to control; URP showed no significant increase. Data suggests low concentrations of UII and URP induce different post‐activation events. A charged residue at the n‐terminal of the cyclic region may alter receptor conformation upon binding. Grant Funding Source : Supported By NIH Grant# R00DA024754‐05S1