Stefanova Iliyana D, Argirova Mariana D, Krustev Athanas D
Department of Biophysics, Medical University, Plovdiv, Bulgaria.
Mol Nutr Food Res. 2007 Apr;51(4):468-72. doi: 10.1002/mnfr.200600110.
Melanoidins obtained from L-arginine and D-glucose (MW > 3500 Da) were tested for their ability to influence the contractility of gastric smooth muscles. A study within the range 0.1-10 mg/mL revealed that at low concentrations, the melanoidins provoked concentration-dependent contraction, whereas a muscle relaxation was registered at high concentrations. The contraction was preceded by changes in the calcium membrane current as measured by single sucrose-gap method and significantly attenuated by the calcium channel blockers D-600 and nifedipine. Measurements with Ca(2+)-selective electrode showed that the melanoidins decreased the concentration of ionized Ca(2+ )in tissue bath in concentration-dependent manner. Experiments carried out in solutions with lower than normal Ca(2+) concentration and using melanoidins preliminary saturated with Ca(2+ )confirmed that the calcium chelation by melanoidins was a key contributing cause for the development of relaxant response. The results obtained showed that the melanoidins could influence the contractility of smooth muscles through at least two pathways: at low concentrations they caused depolarization and activation of L-type calcium channels, stimulated the Ca(2+ )influx, and provoked contraction, whereas at high concentrations calcium binding by melanoidins led to significant depletion of extracellular calcium ions and contributed to the relaxation process observed.
对从L-精氨酸和D-葡萄糖中获得的类黑素（分子量>3500道尔顿）影响胃平滑肌收缩性的能力进行了测试。在0.1 - 10毫克/毫升范围内的一项研究表明，在低浓度时，类黑素引发浓度依赖性收缩，而在高浓度时则出现肌肉松弛。通过单蔗糖间隙法测量，收缩之前钙膜电流发生变化，并且钙通道阻滞剂D-600和硝苯地平可显著减弱这种变化。用Ca(2+)选择性电极测量表明，类黑素以浓度依赖性方式降低组织浴中离子化Ca(2+)的浓度。在低于正常Ca(2+)浓度的溶液中进行的实验以及使用预先用Ca(2+)饱和的类黑素的实验证实，类黑素的钙螯合是产生松弛反应的关键促成因素。所获得的结果表明，类黑素可通过至少两条途径影响平滑肌的收缩性：在低浓度时，它们引起L型钙通道的去极化和激活，刺激Ca(2+)内流并引发收缩，而在高浓度时，类黑素与钙结合导致细胞外钙离子显著耗尽，并促成了所观察到的松弛过程。
