Ljungström M, Chew C S
Department of Physiology, Morehouse School of Medicine, Atlanta, Georgia 30310-1495.
Am J Physiol. 1991 Jan;260(1 Pt 1):C67-78. doi: 10.1152/ajpcell.1991.260.1.C67.
Calcium is an important regulator of cellular activities including HCl secretion by parietal cells. With cholinergic agonists, a role for calcium is established; however, with histamine, at least two signaling pathways may be involved including calcium and adenosine 3',5'-cyclic monophosphate (cAMP). Because chelation of medium and/or cellular calcium has pronounced inhibitory effects on cholinergic but lesser effects on histamine-stimulated acid secretory responses in cell populations, the calcium pathway may not be of central importance for HCl secretion regulated by histamine. We have used digitized video imaging of fura-2 fluorescence ratios and cellular morphology to determine more precisely the relationship between cellular calcium signaling mechanisms and acid secretion in single cultured rabbit parietal cells. Calcium signaling patterns were found to exhibit striking differences with histamine as compared with the cholinergic agonist carbachol. Maximal doses of histamine initiated repetitive oscillations in intracellular calcium ([Ca2+]i) in approximately 50% of cells, whereas the maximal carbachol response was characterized by a typical initial spike followed by a sustained elevation in [Ca2+]i. Oscillations in response to carbachol were detected only at doses below the half-maximal concentration for initiation of acid secretion. Correlation of gradual expansion of acidic vacuoles with increases in [Ca2+]i in the same cells indicated that approximately 20% of cells increased acid secretory-related activities in response to histamine with no detectable rise in [Ca2+]i. These data suggest two possibilities: 1) a rise in [Ca2+]i is not necessary for histamine-stimulated HCl secretion, or 2) heterogeneous receptor-coupling mechanisms exist in parietal cell populations with either calcium or cAMP mechanisms predominating in different subpopulations. The ability to assess simultaneously acid secretory-related responses and calcium signaling patterns allows, for the first time, correlation of "physiological" and biochemical responses in single parietal cells. This methodology is expected to provide new insight into second messenger control mechanisms that are not possible either in cell populations or acutely isolated parietal cells that do not exhibit morphological transformations detectable at the light microscope level.
钙是细胞活动的重要调节因子，包括壁细胞分泌盐酸。对于胆碱能激动剂，钙的作用已得到证实；然而，对于组胺，可能涉及至少两条信号通路，包括钙和腺苷3',5'-环磷酸（cAMP）。由于培养基和/或细胞内钙的螯合对胆碱能刺激的酸分泌反应有明显的抑制作用，而对组胺刺激的细胞群体酸分泌反应的抑制作用较小，因此钙信号通路对于组胺调节的盐酸分泌可能不是至关重要的。我们使用fura-2荧光比率的数字化视频成像和细胞形态学来更精确地确定单个培养的兔壁细胞中细胞钙信号机制与酸分泌之间的关系。结果发现，与胆碱能激动剂卡巴胆碱相比，组胺的钙信号模式存在显著差异。最大剂量的组胺在约50%的细胞中引发细胞内钙（[Ca2+]i）的重复振荡，而最大卡巴胆碱反应的特征是典型的初始峰值，随后是[Ca2+]i的持续升高。仅在低于引发酸分泌的半数最大浓度的剂量下检测到对卡巴胆碱的振荡反应。同一细胞中酸性液泡的逐渐扩张与[Ca2+]i增加的相关性表明，约20%的细胞对组胺有酸分泌相关活动增加，但[Ca2+]i没有可检测到的升高。这些数据提示两种可能性：1）组胺刺激的盐酸分泌不一定需要[Ca2+]i升高，或者2）壁细胞群体中存在异质性受体偶联机制，在不同亚群中以钙或cAMP机制为主。同时评估酸分泌相关反应和钙信号模式的能力首次实现了单个壁细胞中“生理”反应与生化反应的相关性。预计这种方法将为第二信使控制机制提供新的见解，这在细胞群体或急性分离的壁细胞中是不可能的，因为这些细胞在光学显微镜水平上不表现出可检测到的形态转变。
