Lieste J R, Scheenen W J, Willems P H, Jenks B G, Roubos E W
Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences, University of Nijmegen, The Netherlands.
Cell Calcium. 1996 Oct;20(4):329-37. doi: 10.1016/s0143-4160(96)90038-x.
Intracellular Ca2+ oscillations play an important role in the induction of alpha-MSH release from pituitary melanotrope cells of Xenopus laevis. Oscillatory, secretory and adenylyl cyclase activities are all inhibited by dopamine, neuropeptide Y (NPY) and baclofen (a GABAB receptor agonist) and stimulated by sauvagine. In this study, we test the hypothesis that these neural messengers regulate the Ca2+ oscillations via a cAMP/protein kinase A (PKA)-dependent mechanism. To this end, video-imaging microscopy was applied to single Xenopus melanotropes loaded with the Ca2+ indicator Fura-2. The cAMP-dependent PKA inhibitor H89 blocked Ca2+ oscillations as well as the stimulatory actions of 8-Br-cAMP and sauvagine. Treatment of cells inhibited by baclofen with either 8-Br-cAMP or sauvagine led to a reappearance of Ca2+ oscillations. A similar result was found for cells inhibited by NPY. Neither 8-Br-cAMP nor sauvagine induced Ca2+ oscillations in cells inhibited by dopamine. Depolarizing dopamine-inhibited cells with high potassium also failed to induce oscillations, but combining 8-Br-cAMP with membrane depolarization induced oscillations. It is concluded that sauvagine, baclofen and NPY work primarily through a cAMP/PKA-pathway while dopamine inhibits Ca2+ oscillations in a dual fashion, namely via both a cAMP-dependent and a cAMP-independent mechanism, the latter probably involving membrane hyperpolarization.
细胞内钙离子振荡在非洲爪蟾垂体黑素细胞释放α-促黑素（α-MSH）的诱导过程中发挥重要作用。振荡、分泌及腺苷酸环化酶活性均受到多巴胺、神经肽Y（NPY）和巴氯芬（一种GABAB受体激动剂）的抑制，并受到蛙皮素的刺激。在本研究中，我们检验了如下假设：这些神经信使通过一种环磷酸腺苷/蛋白激酶A（PKA）依赖性机制调节钙离子振荡。为此，将视频成像显微镜应用于加载了钙离子指示剂Fura-2的单个非洲爪蟾黑素细胞。环磷酸腺苷依赖性PKA抑制剂H89阻断了钙离子振荡以及8-溴环磷酸腺苷（8-Br-cAMP）和蛙皮素的刺激作用。用8-Br-cAMP或蛙皮素处理受巴氯芬抑制的细胞会导致钙离子振荡重现。对于受NPY抑制的细胞也发现了类似结果。8-Br-cAMP和蛙皮素均未在受多巴胺抑制的细胞中诱导出钙离子振荡。用高钾使受多巴胺抑制的细胞去极化也未能诱导振荡，但将8-Br-cAMP与膜去极化相结合则诱导出了振荡。得出的结论是，蛙皮素、巴氯芬和NPY主要通过环磷酸腺苷/蛋白激酶A途径起作用，而多巴胺以双重方式抑制钙离子振荡，即通过环磷酸腺苷依赖性和环磷酸腺苷非依赖性机制，后者可能涉及膜超极化。
