Detection of melanocortin-3 receptor mRNA in immature rat pituitary: functional relation to gamma3-MSH-induced changes in intracellular Ca2+ concentration?
We have previously shown that gamma3-MSH stimulates DNA replication in lactotrophs, somatotrophs and thyrotrophs of early postnatal rat pituitary in culture. Since the melanocortin-3 (MC-3) receptor is the only known receptor displaying high affinity for gamma3-MSH, the present study explored whether mRNA of the latter receptor is present in the pituitary and whether the receptor is functional. RT-PCR of RNA extracts from 14-day-old rat pituitary revealed the presence of MC-3 receptor mRNA in both the anterior and the neurointermediate lobe. The identity of the amplified products was confirmed by sequence analysis. Dispersed cells of 14-day-old female rats (24 h in culture) were exposed to gamma3-MSH, and changes in intracellular free calcium levels ([Ca2+]i) were assessed by means of fluo-3 video imaging. Gamma3-MSH evoked a rapid and maintained oscillating [Ca2+]i increase in 5%, 10% and 15% of the cells at a dose of 0.1, 1 and 10 nM, respectively. The MC-3/MC-4 receptor antagonist Ac-Nle4-c[Asp5,(D-Nal(2)7,Lys10]alpha-MSH-(4-10)-NH2 (SHU 9119) blocked the effect of gamma3-MSH in about 50% of the responsive cells. The present data suggest that the MC-3 receptor is expressed in the rat pituitary but that this receptor mediates only half of the effects of its putative ligand, gamma3-MSH, on [Ca2+]i. Part of the effect of gamma3-MSH may be mediated by a MC-3 receptor in a functional state different from the one studied previously in transfected cell lines or by a hitherto unidentified MC receptor.
Lorsignol
A
A
Laboratory of Cell Pharmacology, University of Leuven, Medical School, Campus Gasthuisberg (O & N), Belgium.
Vande Vijver
V
V
Ramaekers
D
D
Vankelecom
H
H
Denef
C
C
D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D017931:DNA Primers; D005260:Female; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism* / Q000494:pharmacology; D010902:Pituitary Gland / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D044104:Receptor, Melanocortin, Type 3; D018043:Receptors, Corticotropin / Q000037:antagonists & inhibitors / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D012333:RNA, Messenger; D044104:Receptor, Melanocortin, Type 3; D018043:Receptors, Corticotropin; C103272:SHU 9119; D009074:Melanocyte-Stimulating Hormones; D002118:Calcium