EXPRESSION CLONING OF A RAT HYPOTHALAMIC GALANIN RECEPTOR-COUPLED TO PHOSPHOINOSITIDE TURNOVER

The neuropeptide galanin is widely distributed throughout the central and peripheral nervous systems and participates in the regulation of p rocesses such as nociception, cognition, feeding behavior, and insulin secretion. Multiple galanin receptors are predicted to underlie its p hysiological effects, We now report the isolation by expression clonin g of a rat galanin receptor cDNA distinct from GALR1. The receptor, te rmed GALR2, was isolated from a Pat hypothalamus cDNA library using a I-125-porcine galanin (I-125-pGAL) binding assay. The GALR2 cDNA encod ed a protein of 372 amino acids exhibiting 38% amino acid identity wit h rat GALR1. Binding of I-125-pGAL to transiently expressed GALR2 rece ptors was saturable (K-D = 0.15 naa) and displaceable by galanin pepti des and analogues in rank order: porcine galanin similar or equal to M 32 similar or equal to M35 similar or equal to M40 greater than or equ al to galanin-(1-16) similar or equal to M15 similar or equal to [D-Tr p(2)]galanin-(1-29) > C7 much greater than galanin-(3-29). This profil e resembles that of the rat, GALR1 receptor with the notable exception that [D-Trp(2)]galanin exhibited significant selectivity for GALR2 ov er GALR1, Activation of GALR2 receptors with porcine galanin and other galanin analogues increased inositol phospholipid turnover and intrac ellular calcium levels in stably transfected Chinese hamster ovary cel ls and generated calcium-activated chloride currents in Xenopus oocyte s, suggesting that the rat. GALR2 receptor is primarily coupled to the activation of phospholipase C.