Grégoire G, Pacaud P, Loirand G
Laboratoire de Physiologie, Faculté de médecine Victor Pachon, Université de Bordeaux II, France.
Cell Calcium. 1995 Dec;18(6):505-14. doi: 10.1016/0143-4160(95)90013-6.
Stimulation of portal vein myocytes with noradrenaline (NA) in the presence of a voltage-dependent Ca2+ channel blocker, evoked a transient increase in the concentration of free cytosolic Ca2+, due to inositol 1,4,5-trisphosphate mediated Ca2+ release, followed by activation of a Ca2+ entry pathway. Combining patch-clamp and indo-1 measurements we have tested the effects of various pharmacological agents on this Ca2+ entry following NA-induced Ca2+ release in order to determine the mechanism involved. Only the guanylate cyclase inhibitor LY-83583 specifically inhibited the maintained Ca2+ entry during NA stimulation. This inhibition was reversed by dibutyryl cGMP (DB-cGMP) or 8-bromo cGMP. Under control conditions, addition of DB-cGMP to the external solution was without effect. Thapsigargin and caffeine each depleted the intracellular Ca2+ store but did not evoke Ca2+ entry in venous myocytes under control conditions. However, application of DB-cGMP or NA after Ca2+ store depletion induced by caffeine or thapsigargin caused a rise in [Ca2+]i by activation of a Ca2+ entry pathway. The effect of cGMP seems to involve phosphorylation since cGMP-activated protein kinase inhibitors KT-5823 and H-8 blocked the NA-induced Ca2+ entry. Our results thus suggest that the activation of the voltage-independent Ca2+ entry by NA involves an increase in cellular cGMP.
在存在电压依赖性钙通道阻滞剂的情况下，用去甲肾上腺素（NA）刺激门静脉肌细胞，由于肌醇1,4,5 - 三磷酸介导的钙释放，引起游离胞质钙浓度的短暂升高，随后激活钙内流途径。结合膜片钳和indo - 1测量，我们测试了各种药理剂对NA诱导钙释放后这种钙内流的影响，以确定其中涉及的机制。只有鸟苷酸环化酶抑制剂LY - 83583特异性抑制了NA刺激期间持续的钙内流。这种抑制作用可被二丁酰环鸟苷酸（DB - cGMP）或8 - 溴环鸟苷酸逆转。在对照条件下，向外部溶液中添加DB - cGMP没有效果。毒胡萝卜素和咖啡因各自耗尽了细胞内钙储存，但在对照条件下并未在静脉肌细胞中引起钙内流。然而，在由咖啡因或毒胡萝卜素诱导的钙储存耗尽后应用DB - cGMP或NA，通过激活钙内流途径导致细胞内钙浓度升高。cGMP的作用似乎涉及磷酸化，因为cGMP激活的蛋白激酶抑制剂KT - 5823和H - 8阻断了NA诱导的钙内流。因此，我们的结果表明，NA激活非电压依赖性钙内流涉及细胞内cGMP的增加。
