Abdel-Malak Rania, Ahearn Gregory A
Department of Biology, University of North Florida, Jacksonville, Florida.
J Exp Zool A Ecol Genet Physiol. 2014 Mar;321(3):135-43. doi: 10.1002/jez.1843. Epub 2013 Nov 19.
Effects of luminal Ca(2+) and Mn(2+) on transmural mucosal to serosal (MS) transport of (3) H-L-leucine were characterized in the isolated and perfused intestine of the American lobster, Homarus americanus. (3) H-L-leucine MS transport in the presence of 20 µM Mn(2+) was a sigmoidal function of luminal amino acid concentration, following the Hill equation for multisite cooperative, carrier-mediated, transport. Luminal Ca(2+) was a non-competitive inhibitor of Mn(2+) -stimulated (3) H-L-leucine MS flux. Amino acid transport was hyperbolically stimulated by luminal Ca(2+) or Mn(2+). During 20 µM Mn(2+) -stimulation of (3) H-L-leucine MS flux, addition of 25 mM Ca(2+) strongly reduced amino acid transport Jmax , without affecting amino acid binding properties. Hyperbolic luminal Mn(2+) stimulation of 20 µM (3) H-L-leucine MS flux was also strongly inhibited by 25 mM luminal Ca(2+) , significantly reducing 20 µM (3) H-L-leucine Jmax . Increasing the luminal concentration of verapamil, a calcium channel blocker, significantly increased MS transport of 20 µM (3) H-L-leucine in the presence of 100 nM Mn(2+) by reducing diffusional Ca(2+) uptake into intestinal epithelial cells through verapamil-sensitive channels. A model is proposed supporting the concept of molecular mimicry, whereby (3) H-L-leucine enters lobster intestinal epithelial cells by one or more amino acid-specific transporters and by a dipeptide-like transporter that is capable of binding and transporting peptide molecular mimics (bis-complexes) between Ca(2+) or Mn(2+) and (3) H-L-leucine using the membrane potential as a major driving force for the transport event. According to the model, Ca(2+) entry through apical Ca(2+) channels regulates the magnitude of the membrane potential and therefore the size of the driving force for bis-complex uptake.
研究了管腔Ca(2+)和Mn(2+)对美洲龙虾（美洲螯龙虾）离体灌注肠道中(3)H-L-亮氨酸跨壁黏膜到浆膜（MS）转运的影响。在20 μM Mn(2+)存在下，(3)H-L-亮氨酸的MS转运是管腔氨基酸浓度的S形函数，遵循多位点协同、载体介导转运的希尔方程。管腔Ca(2+)是Mn(2+)刺激的(3)H-L-亮氨酸MS通量的非竞争性抑制剂。氨基酸转运受到管腔Ca(2+)或Mn(2+)的双曲线刺激。在20 μM Mn(2+)刺激(3)H-L-亮氨酸MS通量期间，添加25 mM Ca(2+)会强烈降低氨基酸转运的最大转运速率（Jmax），而不影响氨基酸结合特性。25 mM管腔Ca(2+)也强烈抑制20 μM (3)H-L-亮氨酸MS通量的双曲线管腔Mn(2+)刺激，显著降低20 μM (3)H-L-亮氨酸的Jmax。增加钙通道阻滞剂维拉帕米的管腔浓度，通过减少通过维拉帕米敏感通道进入肠上皮细胞的扩散性Ca(2+)摄取，在100 nM Mn(2+)存在下显著增加20 μM (3)H-L-亮氨酸的MS转运。提出了一个支持分子模拟概念的模型，据此(3)H-L-亮氨酸通过一种或多种氨基酸特异性转运体以及一种二肽样转运体进入龙虾肠上皮细胞，该二肽样转运体能够利用膜电位作为转运事件的主要驱动力，结合并转运Ca(2+)或Mn(2+)与(3)H-L-亮氨酸之间的肽分子模拟物（双复合物）。根据该模型，通过顶端Ca(2+)通道进入的Ca(2+)调节膜电位的大小，从而调节双复合物摄取的驱动力大小。
