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This Article Full Text Full Text (PDF) All Versions of this Article: JOE-09-0057v1 202/3/463    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Reindl, K. M Articles by Sheridan, M. A PubMed PubMed Citation Articles by Reindl, K. M Articles by Sheridan, M. A

Department of Biological Sciences, North Dakota State University, PO Box 6050, Dept. 2715, Fargo, North Dakota 58108-6050, USA

(Correspondence should be addressed to M A Sheridan; Email: mark.sheridan{at}ndsu.edu)

Previously, we isolated and characterized two distinct GH receptor (GHR)-encoding mRNAs, ghr1 and ghr2, from rainbow trout. In this study, Chinese hamster ovary-K1 cells were individually transfected with plasmids that contained cDNAs encoding rainbow trout ghr1 or ghr2. High affinity binding of ¹²⁵I-salmonid GH (sGH) by the expressed receptors was saturable, displaceable, and ligand selective. Whole-cell binding analysis revealed a single class of binding site; for Ghr1 K_d=8 nM, for Ghr2 K_d=17 nM. While salmonid prolactin (sPrl) displaced ¹²⁵I-sGH from both Ghr1 and Ghr2, the affinity of either receptor subtype for sPrl was substantially less than for sGH; salmonid somatolactin, another member of the GH–PRL family, did not displace labeled sGH except at pharmacological concentrations. ¹²⁵I-sGH was internalized by Ghr1- and Ghr2-expressing cells in a time-dependent manner; the maximum internalization reached was 71% for Ghr1 and 55% for Ghr2. Long-term exposure (24 h) of transfected cells to sGH up-regulated surface expression of both Ghr1 and Ghr2; however, sGH induced surface expression of Ghr1 to a greater extent than that of Ghr2. These results indicate that rainbow trout ghrs display both overlapping and distinct characteristics that may be important for ligand selection and differential action in target organs.