Scheenen W J, Jenks B G, Willems P H, Roubos E W
Department of Animal Physiology, University of Nijmegen, The Netherlands.
Pflugers Arch. 1994 Jun;427(3-4):244-51. doi: 10.1007/BF00374530.
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.
非洲爪蟾垂体中叶促黑素细胞分泌的α-促黑素细胞激素（α-MSH）受多种神经因子调节，包括经典神经递质和神经肽。这些细胞中的大多数（80%）呈现自发的Ca2+振荡。为了更好地理解促黑素细胞内Ca2+（[Ca2+]i）的外部调节机制，我们研究了已知的α-MSH促分泌剂对Ca2+振荡的作用。结果表明，所有测试的促分泌剂也能控制非洲爪蟾促黑素细胞的振荡状态，即促分泌抑制剂多巴胺、异鹅肌肽（γ-氨基丁酸，GABAA激动剂）、巴氯芬（GABAB激动剂）和神经肽Y能迅速抑制自发的Ca2+振荡，而促分泌刺激剂蛙皮素（一种与促肾上腺皮质激素释放激素相关的两栖类肽）能在非振荡细胞中诱导振荡活动。这支持了Ca2+振荡的调节是促黑素细胞分泌活性调节的关键点这一观点。促黑素细胞对促分泌剂处理的Ca2+反应阈值存在相当大的异质性。这种异质性可能是动物在生理适应过程中观察到的促黑素细胞募集的基础。
