Rodriguez-Pascual F, Miras-Portugal M T, Torres M
Dpto. Bioquímica, Fac. Veterinaria, Universidad Complutense de Madrid, Spain.
Biochem Pharmacol. 1995 Sep 7;50(6):763-9. doi: 10.1016/0006-2952(95)00196-7.
The production of cyclic GMP (cGMP) induced by acetylcholine and other stimuli was studied in bovine chromaffin cells. Acetylcholine increased intracellular cGMP in a transitory (peak at 2 min) and concentration-dependent manner (estimated half maximal increase, EC50 = 61 +/- 5 microM). NG-nitro-L-arginine methyl ester (NAME) inhibited such a rise in cGMP with a half maximal inhibitory concentration (IC50) of 231 +/- 55 microM. The acetylcholine-induced increase in cGMP was also inhibited by a calmodulin antagonist (calmidazolium, 30 microM) and by the absence of extracellular calcium. Other agents that strongly increased cytosolic calcium concentration ([Ca2+]i) as acetylcholine did, such as the nicotinic-agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP), high-KCl (50 mM), and ionomycin, also caused a rise in cGMP in cultured bovine chromaffin cells. Veratridine, an activator of sodium channels, produced a slowly developing calcium increase and no significant cGMP production. The muscarinic-agonist, muscarine, failed to increase cytosolic calcium, and was the weakest stimulator of cGMP production. cGMP formation, induced by sodium nitroprusside (SNP, 100 microM) and by C-type natriuretic peptide (CNP, 100 nM), was inhibited by 30-40% by increasing [Ca2+]i with ionomycin. This inhibition was abolished by calmidazolium (30 microM) and by the absence of calcium in the extracellular medium. In conclusion, bovine chromaffin cells synthesize nitric oxide (NO) to activate guanylate cyclase in response to several stimuli, which increase [Ca2+]i. Moreover, the increase in [Ca2+]i also stimulates a Ca2+/calmodulin phosphodiesterase, which could down-regulate the levels of cGMP in these cells.
研究了乙酰胆碱和其他刺激物诱导牛嗜铬细胞中环状鸟苷酸（cGMP）的产生情况。乙酰胆碱以短暂的方式（2分钟时达到峰值）和浓度依赖性方式增加细胞内cGMP（估计半数最大增加量，EC50 = 61±5微摩尔）。NG-硝基-L-精氨酸甲酯（NAME）抑制cGMP的这种升高，其半数最大抑制浓度（IC50）为231±55微摩尔。乙酰胆碱诱导的cGMP增加也受到钙调蛋白拮抗剂（氯米帕明，30微摩尔）和细胞外无钙环境的抑制。其他像乙酰胆碱一样强烈增加胞质钙浓度（[Ca2+]i）的试剂，如烟碱激动剂1,1-二甲基-4-苯基哌嗪鎓（DMPP）、高钾（50毫摩尔）和离子霉素，也会导致培养的牛嗜铬细胞中cGMP升高。藜芦碱，一种钠通道激活剂，会使钙缓慢增加且不会产生显著的cGMP生成。毒蕈碱激动剂毒蕈碱未能增加胞质钙，并且是cGMP生成的最弱刺激剂。硝普钠（SNP，100微摩尔）和C型利钠肽（CNP，100纳摩尔）诱导的cGMP形成，通过离子霉素增加[Ca2+]i会被抑制30 - 40%。这种抑制作用被氯米帕明（30微摩尔）和细胞外培养基中无钙环境消除。总之，牛嗜铬细胞会合成一氧化氮（NO）以响应几种增加[Ca2+]i的刺激物来激活鸟苷酸环化酶。此外，[Ca2+]i的增加还会刺激一种钙/钙调蛋白磷酸二酯酶，这可能会下调这些细胞中cGMP的水平。
