虹鳟和大鼠松果体细胞内游离钙离子浓度的调控。

H W Korf, S Kroeber, C Schomerus
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引用次数: 10

摘要

钙离子与cAMP一起在所有脊椎动物松果体器官中褪黑激素合成的调控中发挥重要作用,而不考虑产生褪黑激素的松果体细胞的明显系统发育转化。在这里,我们解决了在直接光敏的鳟鱼松果体细胞和失去直接光敏并对去甲肾上腺素作出反应的大鼠松果体细胞中,细胞内自由钙离子[Ca2+]i的浓度是如何调节的问题。采用fura-2技术、图像分析和膜片钳记录技术对经s抗原免疫反应鉴定的分离松果体细胞进行研究。大约30%的鳟鱼松果体细胞表现出自发的[Ca2+]i振荡,不受细胞的光或暗适应的影响。去除细胞外Ca2+或应用10微米硝苯地平引起可逆的[Ca2+]i振荡击穿。60 mM氯化钾和硝苯地平处理表明,电压门控l型钙通道在振荡和非振荡鳟鱼松果体细胞中对[Ca2+]i的调节中起主要作用。thapsigargin(2微米)的实验显示,80%的鳟鱼松果体细胞中存在细胞内钙储存,但它们在调节[Ca2+]i中的作用尚不清楚。去甲肾上腺素对鳟鱼松果体细胞[Ca2+]i无明显影响。在大鼠松果体细胞中,[Ca2+]i没有自发振荡。去甲肾上腺素通过刺激α 1-肾上腺素能受体,在95%以上的细胞中引起[Ca2+]i的显著双相升高。这种反应反映了细胞内的钙动员、素敏感的钙储存和钙流入增加的结合。大鼠松果体细胞膜中存在l型电压门控钙通道,但它们不参与去甲肾上腺素诱导的钙反应。然而,这些通道介导钙内流的增加,几乎在所有大鼠松果体细胞中观察到乙酰胆碱或尼古丁刺激。结果表明,松果体细胞中[Ca2+]i的调节机制是复杂的,并且在哺乳动物和变温动物之间存在很大差异。
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Regulation of the intracellular concentration of free calcium ions in pinealocytes of the rainbow trout and the rat.
Together with cAMP, calcium ions play an important role in the regulation of melatonin synthesis in the pineal organ of all vertebrate species, irrespective of the conspicuous phylogenetic transformation of the melatonin-producing cell, the pinealocyte. Here we address the question how the intracellular concentration of free calcium ions [Ca2+]i is regulated in directly light-sensitive trout pinealocytes and in rat pinealocytes which have lost the direct light sensitivity and respond to norepinephrine. Isolated pinealocytes identified by the S-antigen immunoreaction were investigated by means of the fura-2 technique, image analysis and patch clamp recordings. Approximately 30% of the trout pinealocytes exhibited spontaneous [Ca2+]i oscillations that were not affected by light or dark adaptation of the cells. Removal of extracellular Ca2+ or application of 10 microM nifedipine caused a reversible breakdown of the [Ca2+]i oscillations. Treatments with 60 mM KCl and nifedipine suggest that voltage-gated L-type calcium channels play a major role in the regulation of [Ca2+]i in both oscillating and nonoscillating trout pinealocytes. Experiments with thapsigargin (2 microM) revealed the presence of intracellular calcium stores in 80% of the trout pinealocytes, but their role in the regulation of [Ca2+]i remains elusive. Norepinephrine had no apparent effect on [Ca2+]i in any trout pinealocyte. In rat pinealocytes, [Ca2+]i did not show spontaneous oscillations. Norepinephrine evoked a dramatic biphasic rise in [Ca2+]i in more than 95% of the cells via stimulation of alpha1-adrenergic receptors. The response reflects a combination of calcium mobilization from intracellular, thapsigargin-sensitive calcium stores and an increased calcium influx. Voltage-gated calcium channels of the L-type are present in the rat pinealocyte membrane, but they are not involved in the norepinephrine-induced calcium response. These channels, however, mediate the increase in calcium influx which is observed in virtually all rat pinealocytes upon stimulation with acetylcholine or nicotine. The results show that the mechanisms which regulate [Ca2+]i in pinealocytes are complex and differ considerably between poikilothermic and mammalian species.
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