Specific binding of [3H-Tyr8]physalaemin to rat submaxillary gland substance P receptor.
[3H]Physalaemin [( 3H]PHY) binds to a single class of noninteracting sites on rat submaxillary gland membranes suspended in high ionic strength media with a KD of 2.7 nM, a Bmax of 240 fmol/mg of protein, and low nonspecific binding. The relative potencies of substance P (SP) and its fragments in competing with [3H]PHY correlate with their relative salivation potencies. This indicates that [3H]PHY interacts with a physiologically relevant SP receptor. In low ionic strength media, the KD of [3H]PHY does not change, but SP and some of its fragments are more potent than PHY in competing with [3H] PHY. Computer-assisted analysis of [3H]PHY and [3H]SP binding in high and low ionic strength media demonstrated that both peptides are equipotent in high ionic strength but that the affinity of SP increases by 70-fold in low ionic strength. The SP fragments that contain a basic residue in positions 1 and/or 3 also display an increased affinity in low ionic strength. These findings document that [3H]PHY binding in high ionic strength (mu = 0.6) accurately reflects the pharmacological potencies of agonists on the SP-P receptor. The binding of [3H]PHY, like that of [3H]SP, increases by the addition of divalent cations (Mg2+ greater than Ca2+ greater than Mn2+). Guanine nucleotides decrease [3H]PHY binding by decreasing the Bmax to the same level (160 fmol/mg of protein), in the presence or absence of Mg2+.
Bahouth
S W
SW
Lazaro
D M
DM
Brundish
D E
DE
Musacchio
J M
JM
D000818:Animals; D001667:Binding, Competitive; D007700:Kinetics; D007705:Kinins / Q000378:metabolism*; D009994:Osmolar Concentration; D010803:Physalaemin / Q000138:chemical synthesis / Q000378:metabolism*; D051381:Rats; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013363:Submandibular Gland / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*; D014316:Tritium
D007705:Kinins; D018040:Receptors, Neurokinin-1; D017981:Receptors, Neurotransmitter; D014316:Tritium; D010803:Physalaemin; D013373:Substance P