Expression of the melanin-concentrating hormone receptor in porcine and human ciliary epithelial cells

PURPOSE. To evaluate whether the receptors for melanin-concentrating hormon e (MCH) and its functional antagonist alpha -melanocyte-stimulating hormone (alpha -MSH) are expressed in the ciliary epithelium. Furthermore, to exam ine whether MCH, a neuropeptide involved in fluid and electrolyte homeostas is, may influence ion flux mediated by Na,K (adenosine triphosphatase)-ATPa se 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 huma n nonpigmented ciliary epithelial (NPE) cell line, ODM-2 was investigated b y radioligand binding studies and reverse transcription-polymerase chain re action (RT-PCR). The MCH-R nas further characterized by photocrosslinking. Influence of MCH on Na,K;-ATPase activity Nas 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 l evel, 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 huma n and porcine origin but the absence of MSPI-Rs indicates that in these cel ls, MCH and alpha -MSH do not form a functionally antagonistic hormonal pai r as they do in several other systems. Although effects of MCH on intestina l water and ion transport have been documented, a direct control of Na,K-AT Pase activity was not detected in human NPE cells in vitro.