Charles S, Henquin J C
Biochem J. 1983 Sep 15;214(3):899-907. doi: 10.1042/bj2140899.
The effects of three types of amino acids on 45Ca2+ fluxes in rat pancreatic islets have been compared. Alanine, a non-insulinotropic neutral amino acid, transported with Na+, increased 45Ca2+ efflux in the presence or in the absence of extracellular Ca2+, but not in the absence of Na+. Its effects in Na+-solutions were practically abolished by 7 mM-glucose. Alanine slightly stimulated 45Ca2+ influx (5 min uptake) only when Na+ was present. Two insulinotropic cationic amino acids (arginine and lysine) triggered similar changes in 45Ca2+ efflux. They accelerated the efflux in the presence of Ca2+ and inhibited the efflux in a Ca2+-free medium, whether glucose was present or not. In an Na+-free Ca2+-medium, arginine and lysine markedly accelerated 45Ca2+ efflux, but this effect was suppressed by 7 mM-glucose. Arginine stimulated 45Ca2+ influx irrespective of the presence or absence of glucose and Na+. Leucine, a neutral insulinotropic amino acid well metabolized by islet cells, inhibited 45Ca2+ efflux from the islets in a Ca2+-free medium; this effect was potentiated by glutamine. In the presence of Ca2+ and Na+, leucine was ineffective alone, but triggered a marked increase in 45Ca2+ efflux when combined with glutamine. In an Na+-free Ca2+-medium, leucine accelerated 45Ca2+ efflux to the same extent with or without glutamine. Leucine also stimulated 45Ca2+ influx in the presence or in the absence of Na+, but its effects were potentiated by glutamine only in the presence of Na+. The results show that amino acids of various types cause distinct changes in 45Ca2+ fluxes in pancreatic islets. Certain of these changes involve an Na+-mediated mobilization of cellular Ca2+ from sequestering sites where glucose appears to exert an opposite effect.
比较了三种氨基酸对大鼠胰岛中(^{45}Ca^{2 +})通量的影响。丙氨酸是一种无促胰岛素分泌作用的中性氨基酸，与(Na^{+})协同转运，在有或无细胞外(Ca^{2 +})存在时均可增加(^{45}Ca^{2 +})外流，但在无(Na^{+})时则无此作用。在(Na^{+})溶液中，其作用实际上被(7 mM)葡萄糖消除。丙氨酸仅在有(Na^{+})存在时轻微刺激(^{45}Ca^{2 +})内流（5分钟摄取）。两种促胰岛素分泌的阳离子氨基酸（精氨酸和赖氨酸）引发了(^{45}Ca^{2 +})外流的类似变化。它们在有(Ca^{2 +})存在时加速外流，在无(Ca^{2 +})的培养基中抑制外流，无论有无葡萄糖。在无(Na^{+})的(Ca^{2 +})培养基中，精氨酸和赖氨酸显著加速(^{45}Ca^{2 +})外流，但这种作用被(7 mM)葡萄糖抑制。精氨酸无论有无葡萄糖和(Na^{+})均刺激(^{45}Ca^{2 +})内流。亮氨酸是一种胰岛细胞易于代谢的中性促胰岛素分泌氨基酸，在无(Ca^{2 +})的培养基中抑制胰岛中(^{45}Ca^{2 +})外流；谷氨酰胺可增强此作用。在有(Ca^{2 +})和(Na^{+})存在时，亮氨酸单独无效，但与谷氨酰胺联合时可引发(^{45}Ca^{2 +})外流显著增加。在无(Na^{+})的(Ca^{2 +})培养基中，亮氨酸无论有无谷氨酰胺均以相同程度加速(^{45}Ca^{2 +})外流。亮氨酸在有或无(Na^{+})存在时也刺激(^{45}Ca^{2 +})内流，但其作用仅在有(Na^{+})存在时被谷氨酰胺增强。结果表明，不同类型的氨基酸可引起胰岛中(^{45}Ca^{2 +})通量的明显变化。其中某些变化涉及由(Na^{+})介导的细胞内(Ca^{2 +})从储存位点的动员，而葡萄糖似乎对此有相反作用。
