Similar rates of phosphatidylinositol hydrolysis following activation of wild-type and truncated rat neurokinin-1 receptors.
The substance P (neurokinin-1) receptor belongs to the family of seven putative transmembrane domain receptors that are coupled via G proteins to phospholipase C activation. Homologous desensitization of substance P-stimulated responses has been described in various systems. The rat neurokinin-1 receptor and a truncated mutant lacking the carboxyl-terminal region were expressed in Chinese hamster ovary cells to examine the mechanisms of substance P-induced desensitization. Wild-type and truncated receptor-bearing cells were indistinguishable in agonist binding affinity and EC50 of substance P-induced accumulation of 3H-inositol phosphates. Substance P-induced responses continued for 30-45 min in cells expressing wild-type and truncated receptors as well as in rat LRM-55 and human U373 cells, which express endogenous neurokinin-1 receptors. In transfected cells expressing the wild-type receptor, CP-96,345 added 15 min after substance P blocked further responses, demonstrating the continuing presence of responsive receptors. The rates of accumulation of 3H-inositol phosphates were four times greater in the initial 15 s of stimulation than for the next 20 min for both wild-type and truncated receptor types. This decrease in rate of substance P-stimulated phosphatidylinositol hydrolysis is therefore not dependent on the carboxyl-terminal region of the rat neurokinin-1 receptor, which contains 26 serine and threonine residues. These results are discussed in relation to current ideas regarding neurokinin-1 receptor desensitization.
Raddatz
R
R
Department of Anatomy and Neurobiology, Washington University School of Medicine, Saint Louis, Missouri 63110.
Crankshaw
C L
CL
Snider
R M
RM
Krause
J E
JE
D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D007295:Inositol Phosphates / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D018040:Receptors, Neurokinin-1 / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D013373:Substance P / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection
D001713:Biphenyl Compounds; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D018040:Receptors, Neurokinin-1; D011994:Recombinant Proteins; D013373:Substance P; C066892:CP 96345