Taniguchi H, Tanaka Y, Hirano H, Tanaka H, Shigenobu K
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi-City, Chiba, Japan.
Naunyn Schmiedebergs Arch Pharmacol. 1999 Jul;360(1):69-79. doi: 10.1007/s002109900033.
A23187 (6S-[6alpha,8beta,9beta,11alpha]-5-(methylamino) -2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)ethyl]-1,7- dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazolecarboxylic acid, calcimycin), an antibiotic Ca2+ ionophore, produces an endothelium-dependent vascular relaxation. In the present study, pharmacological features were functionally characterized of endothelium-dependent relaxant response of guinea-pig aorta to A23187, especially focusing on the possible Ca2+ source and Ca2+ mobilization mechanisms in endothelial cells responsible for the vasorelaxant response to the Ca2+ ionophore. A23187-induced endothelium-dependent relaxation was suppressed profoundly by N(G)-nitro-L-arginine (L-NNA; 3 x 10(-4) M) or calmidazolium (3 x 10(-5) M), suggesting that nitric oxide (NO) produced by the enhanced activation of Ca2+/calmodulin-dependent endothelial NO synthase (eNOS) is largely responsible for the relaxant response of this artery to A23187. In the Ca2+-free solution without EGTA, NO-mediated endothelium-dependent relaxation induced by A23187 was almost abolished, which suggests that Ca2+ entry from extracellular space into endothelial cells plays the key role in the A23187-induced functional vasorelaxation. On the other hand, SK&F96365 (1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole; 5 x 10(-5) M) and Ni2+ (3 x 10(-4) M), both of which inhibit capacitative Ca2+ influx through store-operated Ca2+ channels (SOCCs), attenuated significantly NO-mediated endothelium-dependent relaxation by A23187. Furthermore, A23187-induced endothelium-dependent relaxation was suppressed more strongly than endothelium-independent relaxation induced by SIN-1 (3-morpholino-sydnonimine), an NO donor, when aortic preparation was preconstricted with high KCl instead of agonistic stimulation (prostaglandin F2alpha). These findings suggest that NO-mediated endothelium-dependent relaxant response of guinea-pig aorta to A23187 is preceded by the increase in endothelial cytosolic free Ca2+ concentration ([Ca2+]cyt) due to the enhanced Ca2+ influx from extracellular space. In the enhanced Ca2+ entry leading to the stimulation of eNOS and NO-mediated functional relaxant response of guinea-pig aorta to A23187, activation of SOCCs but not the Ca2+ entry through plasma membrane Ca2+-specific routes made by A23187 seems to play the predominant role. It is most likely that A23187 acts primarily at the Ca2+ store sites in endothelial cells, which subsequently depletes stored Ca2+ to activate SOCCs via unidentified mechanisms.
A23187（6S-[6α,8β,9β,11α]-5-(甲氨基)-2-[[3,9,11-三甲基-8-[1-甲基-2-氧代-2-(1H-吡咯-2-基)乙基]-1,7-二氧杂螺[5.5]十一碳-2-基]甲基]-4-苯并恶唑羧酸，即钙霉素），一种抗生素钙离子载体，可产生内皮依赖性血管舒张作用。在本研究中，对豚鼠主动脉对A23187的内皮依赖性舒张反应的药理学特征进行了功能表征，特别关注负责对钙离子载体产生血管舒张反应的内皮细胞中可能的钙离子来源和钙离子动员机制。N(G)-硝基-L-精氨酸（L-NNA；3×10(-4)M）或钙调蛋白拮抗剂（3×10(-5)M）可显著抑制A23187诱导的内皮依赖性舒张，这表明钙离子/钙调蛋白依赖性内皮型一氧化氮合酶（eNOS）的激活增强所产生的一氧化氮（NO）在很大程度上负责该动脉对A23187的舒张反应。在不含EGTA的无钙溶液中，A23187诱导的NO介导的内皮依赖性舒张几乎完全消失，这表明细胞外空间的钙离子进入内皮细胞在A23187诱导的功能性血管舒张中起关键作用。另一方面，SK&F96365（1-[β-[3-(4-甲氧基苯基)丙氧基]-4-甲氧基苯乙基]-1H-咪唑；5×10(-5)M）和Ni2+（3×10(-4)M）均可抑制通过储存操纵性钙离子通道（SOCCs）的容量性钙离子内流，它们可显著减弱A23187介导的NO依赖性内皮舒张。此外，当主动脉标本用高钾而非激动剂刺激（前列腺素F2α）预收缩时，A23187诱导的内皮依赖性舒张比NO供体SIN-1（3-吗啉代-西多胺）诱导的非内皮依赖性舒张受到更强的抑制。这些发现表明，豚鼠主动脉对A23187的NO介导的内皮依赖性舒张反应之前，由于细胞外空间钙离子内流增强，内皮细胞胞质游离钙离子浓度（[Ca2+]cyt）会升高。在导致eNOS激活和豚鼠主动脉对A23187产生NO介导的功能性舒张反应的增强的钙离子内流过程中，SOCCs的激活而非A23187通过质膜钙离子特异性途径的钙离子内流似乎起主要作用。很可能A23187主要作用于内皮细胞中的钙离子储存位点，随后通过未知机制耗尽储存的钙离子以激活SOCCs。
