Galanin receptor and its ligands in the rat hippocampus.
Receptors for the 29-amino-acid peptide, galanin, in membranes from the rat ventral hippocampus were examined using chloramine-T-iodinated porcine galanin as ligand. The equilibrium binding of 125I-galanin showed the presence of a high-affinity binding site (Kd = 1.91 +/- 0.40 nM). The concentration of the high-affinity-binding sites was 107 +/- 15 fmol/mg membrane protein. The on rate constant was estimated to be 2.6 +/- 0.1 M-1 min-1 at 37 degrees C. The affinity of rat galanin (differing in three amino acid residues from the porcine protein) was equal to that of porcine galanin. The 125I--galanin-binding site is a trypsin-sensitive membrane protein, which is heat-denaturated at 60 degrees C within 5 min. The effect of GTP and its analogs and of pertussis-toxin-catalyzed ADP-ribosylation on the binding of 125I-galanin suggest that the galanin receptor is coupled to an inhibitory G protein (Gi protein). 127I-galanin was shown to be a ligand with affinity equal to that of galanin in displacing 125I-galanin. The 125I-galanin-binding site in the ventral hippocampus recognizes as a ligand the tryptic fragments 1-20 and 21-29 of rat galanin and the synthetic fragments 12-29, 18-29 and 21-29 of porcine galanin. None of these afforded full inhibition of the binding of fragment 1-29 of 125I-galanin at a concentration of 1 microM.
Fisone
G
G
Department of Biochemistry, Arrhenius Laboratory, University of Stockholm, Sweden.
Langel
U
U
Carlquist
M
M
Bergman
T
T
Consolo
S
S
Hökfelt
T
T
Undén
A
A
Andell
S
S
Bartfai
T
T
D000818:Animals; D000242:Cyclic AMP / Q000032:analysis; D019004:Galanin; D006150:Guanine Nucleotides / Q000494:pharmacology; D006624:Hippocampus / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D010455:Peptides / Q000378:metabolism*; D037342:Pertussis Toxin; D051381:Rats; D011919:Rats, Inbred Strains; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D006150:Guanine Nucleotides; D009479:Neuropeptides; D010446:Peptide Fragments; D010455:Peptides; D044088:Receptors, Galanin; D011964:Receptors, Gastrointestinal Hormone; D010566:Virulence Factors, Bordetella; D019004:Galanin; D000242:Cyclic AMP; D037342:Pertussis Toxin