Liu P S, Lin Y J, Kao L S
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan, R.O.C.
J Neurochem. 1991 Jan;56(1):172-7. doi: 10.1111/j.1471-4159.1991.tb02577.x.
Caffeine was used to study the intracellular Ca2+ pools of bovine chromaffin cells. Its effects on cytosolic Ca2+ concentration ([Ca2+]i) were examined using fura-2. Caffeine caused a transient increase in [Ca2+]i in the presence or absence of extracellular Ca2+. In the former case, the caffeine-induced [Ca2+]i increase was higher and stayed above the basal value for several minutes. In the latter case, the [Ca2+]i rise was lower and fell to the basal level within 1 min. These results suggest that caffeine increases [Ca2+]i by causing both Ca2+ influx and Ca2+ release from intracellular pools. In the absence of extracellular Ca2+, ionomycin but not caffeine caused a further increase in [Ca2+]i in cells that had been treated with caffeine. Apparently there are at least two intracellular Ca2+ pools, only one of which is sensitive to caffeine. The caffeine-induced [Ca2+]i rise became smaller when the cells were pretreated with the inositol trisphosphate-generating agonists, methacholine and bradykinin. In addition, methacholine was unable to initiate a [Ca2+]i transient after the cells had been treated with caffeine. The results indicate that the caffeine-sensitive Ca2+ pools overlap with the inositol trisphosphate-sensitive pool and that the size of the latter pool is smaller than that of the former. The caffeine-sensitive Ca2+ pools were refilled after high K+ treatment, which suggests that the caffeine-sensitive Ca2+ pools may be important in buffering the cytosolic Ca2+. The effect of caffeine on [Ca2+]i is not due to inhibition of phosphodiesterase. Our results support a Ca2+ entry model in which depletion of intracellular Ca2+ pools controls the rate of Ca2+ entry across the plasma membrane.
咖啡因被用于研究牛嗜铬细胞的细胞内钙库。使用fura-2检测了其对胞质钙浓度（[Ca2+]i）的影响。无论有无细胞外钙，咖啡因都会引起[Ca2+]i的短暂升高。在前一种情况下，咖啡因诱导的[Ca2+]i升高更高，且在几分钟内保持高于基础值。在后一种情况下，[Ca2+]i的升高较低，并在1分钟内降至基础水平。这些结果表明，咖啡因通过引起细胞外钙内流和细胞内钙库释放钙来增加[Ca2+]i。在无细胞外钙的情况下，离子霉素而非咖啡因会使已用咖啡因处理过的细胞中的[Ca2+]i进一步升高。显然，至少存在两个细胞内钙库，其中只有一个对咖啡因敏感。当细胞用生成肌醇三磷酸的激动剂乙酰甲胆碱和缓激肽预处理后，咖啡因诱导的[Ca2+]i升高变小。此外，在细胞用咖啡因处理后，乙酰甲胆碱无法引发[Ca2+]i瞬变。结果表明，对咖啡因敏感的钙库与对肌醇三磷酸敏感的钙库重叠，且后者的大小小于前者。高钾处理后，对咖啡因敏感的钙库会重新充盈，这表明对咖啡因敏感的钙库可能在缓冲胞质钙方面很重要。咖啡因对[Ca2+]i的作用并非由于抑制磷酸二酯酶。我们的结果支持一种钙内流模型，即细胞内钙库的耗竭控制着钙跨质膜进入的速率。
