Ambudkar I S, Baum B J
Clinical Investigations and Patient Care Branch, National Institute of Dental Research, Bethesda, MD 20892.
Biochim Biophys Acta. 1988 Jun 22;941(2):198-208. doi: 10.1016/0005-2736(88)90180-0.
In basolateral membrane vesicles (BLMV) isolated from rat parotid glands, the initial rate of ATP-dependent Ca2+ transport, in the presence of KCl, was approx. 2-fold higher than that obtained with mannitol, sucrose or N-methyl-D-glucamine (NMDG)-gluconate. Only NH4+, Rb+, or Br- could effectively substitute for K+ or Cl-, respectively. This KCl activation was concentration dependent, with maximal response by 50 mM KCl. An inwardly directed KCl gradient up to 50 mM KCl had no effect on Ca2+ transport, while equilibration of the vesicles with KCl (greater than 100 mM) increased transport 15-20%. In presence of Cl-, 86Rb+ uptake was 2.5-fold greater than in the presence of gluconate. 0.5 mM furosemide inhibited 86Rb+ flux by approx. 60% in a Cl- medium and by approx. 20% in a gluconate medium. Furosemide also inhibited KCl activation of Ca2+ transport with half maximal inhibition either at 0.4 mM or 0.05 mM, depending on whether 45Ca2+ transport was measured with KCl (150 mM) equilibrium or KCl (150 mM) gradient. In a mannitol containing assay medium, potassium gluconate loaded vesicles had a higher (approx. 25%) rate of Ca2+ transport than mannitol loaded vesicles. Addition of valinomycin (5 microM) to potassium gluconate loaded vesicles further stimulated (approx. 30%) the Ca2+ transport rate. These results suggest that during ATP dependent Ca2+ transport in parotid BLMV, K+ can be recycled by the concerted activities of a K+ and Cl- coupled flux and a K+ conductance.
在从大鼠腮腺分离出的基底外侧膜囊泡（BLMV）中，在存在氯化钾的情况下，ATP依赖的钙离子转运初始速率比用甘露醇、蔗糖或N-甲基-D-葡糖胺（NMDG）-葡糖酸盐时获得的速率高约2倍。只有铵离子、铷离子或溴离子能分别有效替代钾离子或氯离子。这种氯化钾激活是浓度依赖性的，在50 mM氯化钾时达到最大响应。高达50 mM氯化钾的内向氯化钾梯度对钙离子转运没有影响，而囊泡与氯化钾（大于100 mM）平衡会使转运增加15 - 20%。在存在氯离子的情况下，86铷离子摄取比存在葡糖酸盐时大2.5倍。0.5 mM呋塞米在氯离子介质中抑制86铷离子通量约60%，在葡糖酸盐介质中抑制约20%。呋塞米还抑制钙离子转运的氯化钾激活，半最大抑制浓度为0.4 mM或0.05 mM，这取决于45钙离子转运是在氯化钾（150 mM）平衡还是氯化钾（150 mM）梯度下测量。在含有甘露醇的测定介质中，装载葡糖酸钾的囊泡比装载甘露醇的囊泡具有更高（约25%）的钙离子转运速率。向装载葡糖酸钾的囊泡中添加缬氨霉素（5 microM）进一步刺激（约30%）钙离子转运速率。这些结果表明，在腮腺BLMV中ATP依赖的钙离子转运过程中，钾离子可通过钾离子和氯离子偶联通量以及钾离子电导的协同活动进行循环利用。
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