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Galanin is a peptide hormone which modulates a wide variety of physiological processes, including secretion, muscle contraction, cognitive function, the reproductive axis, and feeding. Two galanin receptor subtypes, GalR1 and GalR2, have been cloned; however, for GalR2 only the rat sequence has been reported in the literature. Our cloning of human GalR2 reveals its amino acid sequence to be 85% identical to rat GalR2 and 39% identical to human GalR1. Binding of [ 125 I]galanin to the human GalR2 receptor transiently expressed in COS-7 cells was saturable (K d = 0.24 nM ± 0.06 nM) with a receptor density of 383 ± 66 fmol/mg protein. Human galanin(1-30) bound with high affinity to the human GalR2 receptor, with a K i value of 0.86 ± 0.12 nM. With the identification of a second galanin receptor subtype, the specific functions of human galanin receptor subtypes can now begin to be addressed.

Syp is a protein tyrosine phosphatase implicated in insulin and growth factor signaling. To evaluate the role of syp in insulin's regulation of plasma glucose, we generated knockout mice. Homozygous knockout mice die prior to day 10.5 of embryonic development. Hemizygous mice express half the levels of syp protein compared with their wild type littermates but do not display any gross morphological changes. Total body weight (age 2-10 weeks) and plasma insulin and glucose levels both in fasting and glucose-challenged states were comparable in the wild type and the hemizygous mice. No differences were observed in insulin-induced glucose uptake in soleus muscle and epididymal fat; insulin inhibition of lipolysis was also similar. We injected insulin into the portal vein of the mice to examine upstream events of the insulin signaling cascade. Tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1 (IRS-1) from hemizygous tissue was similar to that of wild type tissue. Association of the p85 subunit of phosphatidylinositol 3-kinase to IRS-1 increased an average of 2-fold in both groups. We did not observe an increase of IRS-1/syp association after insulin administration, but we did note a significant basal association in both wild type and hemizygous tissue. Our results do not support a major role for syp in the acute in vivo metabolic actions of insulin.