Galanin receptors in human hypothalamus: biochemical and structural analysis.

Galanin receptors have been characterized in normal human hypothalamus using 125I-galanin binding assays. Competition experiments of porcine 125I-galanin binding to human hypothalamic membranes with native human, porcine and rat galanin (10(-11) M to 10(-8) M) gave comparable results with IC50 close to 0.1 nM. Scatchard analysis indicated one type of high affinity binding sites (Kd = 0.11 nM) with a capacity of 460 fmol/mg protein. Galanin-(1-15) and galanin-(2-29) inhibited tracer binding (IC50 = 1.5 nM), galanin-(3-29) and galanin-(10-29) being inactive. The galanin receptor antagonist, galantide, 10(-14) M to 10(-8) M, also strongly displaced binding of 125I-galanin to the human receptor (IC50 close to 0.15 nM). Guanine nucleotides (from 10(-8) M to 10(-4) M) decreased tracer binding to human membranes by increasing the dissociation of the galanin-receptor complexes. Structural analysis by covalent labelling indicated that the human galanin receptor behaves as a monomeric protein with a molecular mass of 54,000 daltons.