Expression of the melanin-concentrating hormone receptor in porcine and human ciliary epithelial cells.
OBJECTIVE
To evaluate whether the receptors for melanin-concentrating hormone (MCH) and its functional antagonist alpha-melanocyte-stimulating hormone (alpha-MSH) are expressed in the ciliary epithelium. Furthermore, to examine whether MCH, a neuropeptide involved in fluid and electrolyte homeostasis, may influence ion flux mediated by Na,K (adenosine triphosphatase)-ATPase in a ciliary epithelial cell line.


METHODS
Expression of MCH receptors (MCH-R) and alpha-MSH receptors (MSH-R) on primary porcine ciliary pigmented epithelial (PE) cells and on a human nonpigmented ciliary epithelial (NPE) cell line, ODM-2 was investigated by radioligand binding studies and reverse transcription-polymerase chain reaction (RT-PCR). The MCH-R was further characterized by photocrosslinking. Influence of MCH on Na, K-ATPase activity was evaluated by an Rb(+) transport assay.


RESULTS
MCH-R expression was observed at both the mRNA and protein levels in PE and NPE cells. In contrast, MSH-Rs were not detectable. At the mRNA level, expression of slc-1 was shown and with crosslinking, a 44-kDa protein was labeled. MCH showed no effect on Na,K-ATPase activity of NPE cells.


CONCLUSIONS
The presence of MCH-R in ciliary epithelial cells of both human and porcine origin but the absence of MSH-Rs indicates that in these cells, MCH and alpha-MSH do not form a functionally antagonistic hormonal pair as they do in several other systems. Although effects of MCH on intestinal water and ion transport have been documented, a direct control of Na,K-ATPase activity was not detected in human NPE cells in vitro.
Hintermann
E
E
Laboratory of Endocrinology, Department of Research, University Eye Clinic, University Hospital and University Children's Hospital, Basel, Switzerland.
Erb
C
C
Talke-Messerer
C
C
Liu
R
R
Tanner
H
H
Flammer
J
J
Eberle
A N
AN
D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D002924:Ciliary Body / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D005136:Eye Proteins / Q000096:biosynthesis / Q000235:genetics*; D015870:Gene Expression; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011869:Radioligand Assay; D011979:Receptors, Pituitary Hormone / Q000096:biosynthesis / Q000235:genetics*; D017481:Receptors, Somatostatin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013552:Swine; D000521:alpha-MSH / Q000096:biosynthesis / Q000235:genetics
D017931:DNA Primers; D005136:Eye Proteins; C103263:MCHR1 protein, human; D012333:RNA, Messenger; D011979:Receptors, Pituitary Hormone; D017481:Receptors, Somatostatin; C092274:melanin-concentrating hormone receptor; D000521:alpha-MSH; D020962:Heterotrimeric GTP-Binding Proteins; D000254:Sodium-Potassium-Exchanging ATPase