BDNF stimulates Ca 2+ oscillation frequency in melanotrope cells of Xenopus laevis: Contribution of IP3-receptor-mediated release of intracellular Ca 2+ to gene expression

Abstract

Pituitary melanotrope cells of the amphibian Xenopus laevis are neuroendocrine cells regulating the animal’s skin color adaptation through secretion of α-melanophore-stimulating hormone (α-MSH). To fulfill this function optimally, the melanotrope cell undergoes plastic changes in structure and secretory activity in response to changed background light conditions. Xenopus melanotrope cells display Ca 2+ oscillations that are thought to drive α-MSH secretion and gene expression. They also produce brain-derived neurotrophic factor (BDNF), which stimulates in an autocrine way the biosynthesis of the α-MSH precursor, pro-opiomelanocortin (POMC). We have used this physiological adaptation mechanism as a model to investigate the role of BDNF in the regulation of Ca 2+ kinetics and Ca 2+-dependent gene expression. By dynamic video imaging of isolated cultured melanotropes we demonstrated that BDNF caused a dose-dependent increase in Ca 2+ oscillation frequency up to 64.7 ± 2.3% of control level. BDNF also induced a transient Ca 2+ peak in Ca 2+-free medium, which was absent when calcium stores were blocked by thapsigargin and 2-aminoethoxydiphenyl borate, indicating that BDNF stimulates acute release of Ca 2+ from IP 3-sensitive intracellular Ca 2+ stores. Moreover, we show that thapsigargin inhibits the expression of BDNF transcript IV (by 61.1 ± 28.8%) but does not affect POMC transcript. We conclude that BDNF mobilizes Ca 2+ from IP 3-sensitive intracellular Ca 2+ stores and propose the possibility that the resulting Ca 2+ oscillations selectively stimulate expression of the BDNF gene.