A SUBSTANCE-P (NEUROKININ-1) RECEPTOR MUTANT CARBOXYL-TERMINALLY TRUNCATED TO RESEMBLE A NATURALLY-OCCURRING RECEPTOR ISOFORM DISPLAYS ENHANCED RESPONSIVENESS AND RESISTANCE TO DESENSITIZATION
Hz. Li et al., A SUBSTANCE-P (NEUROKININ-1) RECEPTOR MUTANT CARBOXYL-TERMINALLY TRUNCATED TO RESEMBLE A NATURALLY-OCCURRING RECEPTOR ISOFORM DISPLAYS ENHANCED RESPONSIVENESS AND RESISTANCE TO DESENSITIZATION, Proceedings of the National Academy of Sciences of the United Statesof America, 94(17), 1997, pp. 9475-9480
Two isoforms of the substance P (SP) receptor, differing in the length
of the cytoplasmic carboxylterminus by approximate to 8 kDa, have bee
n detected previously in rat salivary glands and other tissues, The bi
nding and functional properties of these two isoforms have been Invest
igated using full-length (407 amino acids) and carboxyl-terminally tru
ncated (324 amino acids) rat SP receptors transfected stably into Chin
ese hamster ovary cells, Both the full-length and the truncated recept
or bound radiolabeled SP with a similar K-d (approximate to 0.1 nM), T
he average number of high affinity SP binding sites per cell was 1.0 x
10(5) and 0.3 x 10(5) for the full-length and the truncated SP recept
or, respectively, In both cell lines, SP induced a rapid but transient
Increase in cytosolic calcium concentration ([Ca2+](i)), which consis
ted of the release of Ca2+ from intracellular stores and the influx of
extracellular Ca2+, Both components are dependent on phospholipase C
activation. Although the full-length and the truncated receptor utiliz
e the same calcium pathways, they differ in their EC50 values (0.28 nM
for the full-length; 0.07 nM for the truncated), These differences in
responsiveness may be related to the observed differences in receptor
desensitization. The truncated receptor, in contrast to the full-leng
th receptor, does not undergo rapid and long-lasting desensitization.
Cells possessing the short isoform of the SP receptor would thus be ex
pected to exhibit a prolonged responsiveness.