Action of stimulatory and inhibitory alpha-MSH secretagogues on spontaneous calcium oscillations in melanotrope cells of Xenopus laevis.
The secretion of alpha-melanophore-stimulating hormone (alpha-MSH) from melanotrope cells in the pituitary gland of Xenopus laevis is regulated by various neural factors, both classical neurotransmitters and neuropeptides. The majority of these cells (80%) display spontaneous Ca2+ oscillations. In order to gain a better understanding of the external regulation of intracellular Ca2+ ([Ca2+]i) in the melanotrope cell, we have examined the action of well known alpha-MSH secretagogues on the Ca2+ oscillations. It is shown that all secretagogues tested also control the oscillatory state of Xenopus melanotropes, that is, the secreto-inhibitors dopamine, isoguvacine (gamma-aminobutyric acid, GABAA agonist), baclofen (GABAB agonist) and neuropeptide Y evoked a rapid quenching of the spontaneous Ca2+ oscillations, whereas the secreto-stimulant sauvagine, an amphibian peptide related to corticotropin releasing hormone, induced oscillatory activity in non-oscillating cells. Supporting argument is given for the idea that the regulation of Ca2+ oscillations is a focal point in the regulation of secretory activity of melanotrope cells. There was considerable heterogeneity among melanotrope cells in the threshold of their Ca2+ response to secretagogue treatment. This heterogeneity may be the basis for melanotrope cell recruitment observed during physiological adaptations of the animal to the light intensity of its background.
Scheenen
W J
WJ
Department of Animal Physiology, University of Nijmegen, The Netherlands.
Jenks
B G
BG
Willems
P H
PH
Roubos
E W
EW
D029845:Amphibian Proteins; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004298:Dopamine / Q000494:pharmacology; D009478:Neuropeptide Y / Q000494:pharmacology; D036361:Peptide Hormones; D010455:Peptides / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011963:Receptors, GABA-A / Q000187:drug effects; D018080:Receptors, GABA-B / Q000187:drug effects; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014982:Xenopus laevis; D000521:alpha-MSH / Q000378:metabolism*
D029845:Amphibian Proteins; D009478:Neuropeptide Y; D036361:Peptide Hormones; D010455:Peptides; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D000521:alpha-MSH; D013973:Thyrotropin-Releasing Hormone; C025727:sauvagine; D002118:Calcium; D004298:Dopamine