Frame M D, Milanick M A
Department of Physiology, University of Missouri-Columbia, School of Medicine 65212.
Am J Physiol. 1991 Sep;261(3 Pt 1):C467-75. doi: 10.1152/ajpcell.1991.261.3.C467.
Ca influx via the Na-Ca exchanger into ferret red blood cells is easily measured from a Na-free solution; the intracellular Na concentration is normally approximately 150 mM in ferret red blood cells. We have found that Mn and Cd competitively inhibit Ca influx. Mn influx and Cd influx were a saturable function of the divalent cation concentration, consistent with a carrier mechanism. Indeed, the Km (approximately 10 microM) and the Vmax (usually 1-3 mmol.l packed cells-1.h-1) were similar for Ca, Cd, and Mn. Extracellular Na inhibited divalent cation influx, and intracellular Na stimulated influx. These results are consistent with Na-Cd and Na-Mn influx pathways in ferret red blood cells. Ca (1 mM) almost completely inhibited Mn influx and Cd influx, whereas 1 mM Mg inhibited 5-15%. These results strongly support the notion that Mn and Cd are alternative substrates for Ca on the ferret red cell Na-Ca exchanger. The similarity in the behavior of all three divalent cation places important constraints on kinetic and structural models of the exchanger.
通过钠钙交换体进入雪貂红细胞的钙内流很容易从无钠溶液中测量；雪貂红细胞内的钠浓度通常约为150 mM。我们发现锰和镉竞争性抑制钙内流。锰内流和镉内流是二价阳离子浓度的饱和函数，这与载体机制一致。实际上，钙、镉和锰的米氏常数（约10 μM）和最大反应速度（通常为1 - 3 mmol·l红细胞压积-1·h-1）相似。细胞外钠抑制二价阳离子内流，而细胞内钠刺激内流。这些结果与雪貂红细胞中的钠镉和钠锰内流途径一致。1 mM钙几乎完全抑制锰内流和镉内流，而1 mM镁抑制5 - 15%。这些结果有力地支持了锰和镉是雪貂红细胞钠钙交换体上钙的替代底物这一观点。所有三种二价阳离子行为的相似性对交换体的动力学和结构模型施加了重要限制。
