title: Immunoblotting technique to study release of melanophore-stimulating hormone from individual melanotrope cells of the intermediate lobe of Xenopus laevis.
abstract: The melanotrope cells in the pars intermedia in the pituitary of Xenopus laevis synthesize and release the melanophore-stimulating hormone (alpha MSH), a small peptide that causes skin darkening during the process of background adaptation. Evidence has been found for a heterogeneity in biosynthetic activity of the melanotrope cells. In the present study two questions were addressed: (1) does the melanotrope cell population also show heterogeneous alpha MSH-release, and (2) can this heterogeneity be changed by extracellular messengers? Since dopamine is known to inhibit alpha MSH-release, this messenger is used to study the regulation of the heterogeneity. To quantify alpha MSH-release from individual cells, a cell blotting procedure has been developed for the binding and relative quantification of the small alpha MSH peptide. The immunoblotting procedure involves binding of the cells to a carrier slide and binding of released alpha MSH to a nitrocellulose filter. After immunostaining, the amount of alpha MSH per cell was quantitated by image analysis. Untreated melanotrope cells reveal a distinct variability in alpha MSH-release, some cells showing low secretory activity, whereas others are strongly secreting, indicating heterogeneity of alpha MSH-release. Dopamine treatment strongly inhibits alpha MSH-release from individual cells, resulting in a clearly less pronounced melanotrope cell heterogeneity. The effect of dopamine appears to be dose-dependent as a low dopamine concentration has only a moderate effect on the alpha MSH-release. It is proposed that dopamine is a physiological regulator of the degree of melanotrope cell heterogeneity in alpha MSH-release.
authors.affiliation: Department of Animal Physiology, University of Nijmegen, The Netherlands.
authors.forename: E P
authors.initials: EP
authors.lastname: de Rijk
authors.forename: M
authors.initials: M
authors.lastname: Terlou
authors.forename: P M
authors.initials: PM
authors.lastname: Cruijsen
authors.forename: B G
authors.initials: BG
authors.lastname: Jenks
authors.forename: E W
authors.initials: EW
authors.lastname: Roubos
mesh_terms: D000818:Animals; D004298:Dopamine / Q000494:pharmacology / Q000502:physiology; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation; D015151:Immunoblotting / Q000379:methods*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014982:Xenopus laevis / Q000502:physiology*; D000521:alpha-MSH / Q000378:metabolism*
chemical_list: D000521:alpha-MSH; D004298:Dopamine