López-Burillo S, Agapito-Serrano M T, Garay R P, Macías J F
Department of Biochemistry, School of Medicine, University of Valladolid, Spain.
Eur J Pharmacol. 1995 Apr 28;289(2):259-65. doi: 10.1016/0922-4106(95)90102-7.
Part of the natriuretic mechanism of dihydropyridine Ca2+ channel antagonists involves the inhibition of renal tubular sodium reabsorption. To identify the membrane ion transport system involved in this natriuretic action, we tested nitrendipine on unidirectional 86Rb+ fluxes in Madin-Darby canine kidney (MDCK) cells. To dissect between direct and indirect effects (via cytosolic Ca2+) of nitrendipine, the compound was re-examined on ion fluxes in human erythrocytes. In MDCK cells, external Ca2+ (3 mM), adrenalin (100 microM) and the Ca2+ ionophore A23187 (20 microM) strongly and transiently stimulated 86Rb+ efflux. All these stimulatory actions were fully inhibited by quinine (1 mM) suggesting that they reflect the opening of Ca(2+)-sensitive K+ channels. Nitrendipine was able to inhibit these Ca(2+)-sensitive K+ channels, bit this inhibitory action required concentrations of the compound (approximately 100 microM). Regarding 86Rb+ influx, the most significant result with nitrendipine was a partial inhibition of bumetanide-sensitive 86Rb+ influx. This effect represented a maximal flux inhibition of about 70% and required very low nitrendipine concentrations (IC50 approximately 1 nM). The Ca2+ ionophore A 23187 strongly stimulated bumetanide-sensitive 86Rb+ influx in MDCK cells. Conversely, a very important reduction (approximately 79%) of this influx component was found in Ca2+ depleted cells. In human red blood cells, Na+, K+, Cl- cotransport fluxes were resistant to nitrendipine, even at high concentrations of the compound (100-500 microM). Conversely, Ca(2+)-sensitive K+ channels were inhibited by nitrendipine with IC50 = 6 +/- 3 microM (mean +/- S.E.M., n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)
二氢吡啶类钙通道拮抗剂的排钠机制部分涉及对肾小管钠重吸收的抑制。为了确定参与这种排钠作用的膜离子转运系统，我们在Madin-Darby犬肾（MDCK）细胞中测试了尼群地平对单向⁸⁶Rb⁺通量的影响。为了区分尼群地平的直接和间接作用（通过胞质Ca²⁺），该化合物在人红细胞的离子通量上再次进行了研究。在MDCK细胞中，细胞外Ca²⁺（3 mM）、肾上腺素（100 μM）和Ca²⁺离子载体A23187（20 μM）强烈且短暂地刺激了⁸⁶Rb⁺外流。所有这些刺激作用均被奎宁（1 mM）完全抑制，表明它们反映了Ca²⁺敏感性钾通道的开放。尼群地平能够抑制这些Ca²⁺敏感性钾通道，但这种抑制作用需要该化合物的浓度（约100 μM）。关于⁸⁶Rb⁺内流，尼群地平最显著的结果是对布美他尼敏感的⁸⁶Rb⁺内流的部分抑制。这种作用代表了约70%的最大通量抑制，并且需要非常低的尼群地平浓度（IC50约为1 nM）。Ca²⁺离子载体A 23187强烈刺激MDCK细胞中布美他尼敏感的⁸⁶Rb⁺内流。相反，在Ca²⁺耗尽的细胞中发现该内流成分有非常重要的减少（约79%）。在人红细胞中，即使在该化合物的高浓度（100 - 500 μM）下，Na⁺、K⁺、Cl⁻协同转运通量对尼群地平也有抗性。相反，Ca²⁺敏感性钾通道被尼群地平抑制，IC50 = 6 ± 3 μM（平均值 ± 标准误，n = 3）。（摘要截断于250字）
