Gascon-Barré M, Petit J L, Ethier C, Bilodeau S
Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Québec, Canada.
Cell Calcium. 1997 Nov;22(5):343-56. doi: 10.1016/s0143-4160(97)90019-1.
In vivo, extracellular calcium ([Ca2+]e) homeostasis is maintained within a very narrow range by the calcium regulating hormones. At the cellular level, the response to many agents is transduced by changes in cytosolic Ca2+ ([Ca2+]i) which involves both mobilization of cellular pools and entry of [Ca2+]e through plasma membrane channels. To investigate the cellular effects of chronic hypocalcemia (Ca-) on [Ca2+]i homeostasis, hepatocytes, a cell type well characterized for its [Ca2+]i response, were used. Data indicate that Ca- leads to a significant shift to the left in the basal resting cytosolic Ca2+ concentration distribution curve with half-maximum cumulative frequency of 119 versus 149 nM in Ca- and normal rats (N) respectively (P < 0.0001). The response to the alpha 1-adrenergic agonist phenylephrine (Phe) was also influenced by Ca- with a dampening of the dose-response curve, a significant decrease in the frequency of sustained responses (P < 0.001), and significant changes in the oscillation pattern. Indeed, hepatocytes obtained from Ca- exhibited a higher frequency of large amplitude, low frequency oscillations than N most particularly at the 2 and 5 microM Phe dose while N predominantly exhibited low amplitude, high frequency oscillations on sustained plateaus (P < 0.001). IP3 receptor (IP3R) binding studies and Ca2+ mobilization from IP3-sensitive pools showed that IP3R was highly sensitive to the prevailing Ca2+ with, in the range of resting [Ca2+]i, R affinity significantly lower in Ca- than in N. Upon exposure of permeabilized cells to 25 microM IP3, Ca2+ mobilization from the IP3-sensitive intracellular pool was significantly reduced by Ca- (P < 0.05) suggesting a decrease in the IP3-mobilizable Ca2+ pool in Ca-. Our results indicate that hypocalcemia significantly alters [Ca2+]i signalling by perturbing the initial response to agonist and the [Ca2+]i response pattern. In addition, the decrease in Ca2+ mobilization from IP3-sensitive pools suggests that hypocalcemia may also lead to a decrease in the Ca2+ content of intracellular pools.
在体内，细胞外钙（[Ca2+]e）的稳态通过钙调节激素维持在非常狭窄的范围内。在细胞水平上，许多因素的反应是通过胞质Ca2+（[Ca2+]i）的变化来传导的，这涉及细胞内钙库的动员以及[Ca2+]e通过质膜通道的进入。为了研究慢性低钙血症（Ca-）对[Ca2+]i稳态的细胞效应，使用了肝细胞，这是一种对其[Ca2+]i反应有充分特征描述的细胞类型。数据表明，Ca-导致基础静息胞质Ca2+浓度分布曲线显著左移，Ca-和正常大鼠（N）的半最大累积频率分别为119 nM和149 nM（P < 0.0001）。对α1-肾上腺素能激动剂去氧肾上腺素（Phe）的反应也受到Ca-的影响，剂量反应曲线受到抑制，持续反应的频率显著降低（P < 0.001），并且振荡模式有显著变化。实际上，从Ca-大鼠获得的肝细胞比N大鼠表现出更高频率的大幅度、低频振荡，特别是在2和5 μM Phe剂量时，而N大鼠在持续平台期主要表现出低幅度、高频振荡（P < 0.001）。IP3受体（IP3R）结合研究以及从IP3敏感库中动员Ca2+的研究表明，IP3R对当前的Ca2+高度敏感，在静息[Ca2+]i范围内，Ca-大鼠的R亲和力显著低于N大鼠。当将通透细胞暴露于25 μM IP3时，Ca-导致从IP3敏感细胞内库中动员Ca2+显著减少（P < 0.05），这表明Ca-大鼠中IP3可动员的Ca2+库减少。我们的结果表明，低钙血症通过干扰对激动剂的初始反应和[Ca2+]i反应模式，显著改变了[Ca2+]i信号传导。此外，从IP3敏感库中动员Ca2+的减少表明，低钙血症也可能导致细胞内钙库中Ca2+含量的减少。
