Gallo M P, Malan D, Bedendi I, Biasin C, Alloatti G, Levi R C
Dipartimento di Biologia Animale e dell'Uomo e INFM Unità TO Uni, Università di Torino, Italy.
Pflugers Arch. 2001 Feb;441(5):621-8. doi: 10.1007/s004240000475.
Several effects of nitric oxide (NO) on the control of L-type calcium current (ICa) and of calcium handling in cardiomyocytes have been described. Cardiomyocytes have been shown to express in different conditions all types of nitric oxide synthases (NOS), but the role of NO in the regulation of calcium current remains controversial. Previously, we have shown in guinea pig ventricular cells a stimulatory effect of NOS inhibitors on ICa. Here we investigate the intracellular mechanisms involved in the putative inhibitory role of NO on basal ICa in ventricular cells. The stimulatory effect of the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA) (1 mM) was present also in calcium transient measurements, but only after a preincubation with L-arginine (L-arg, 0.1 mM). The nitric oxide scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO, 0.5 mM) increased peak ICa in a similar manner to NOS inhibitors in whole-cell voltage-clamp experiments. Also ODQ (1H-[1,2,4]oxidiazolo[4,3-a]quinoxaline-1-one, 0.1 mM), a specific inhibitor of a target of NO, the soluble guanylate cyclase, was able to stimulate ICa. The block of type II phosphodiesterase (cGMP-activated) by EHNA (erythro-9-[2-hydroxy-3-nonylladenine, 30 microM) exerted a similar effect on ICa as PTIO and ODQ. Carbachol (CCh, 1 microM) was able to revert the stimulatory effect on ICa observed with PTIO, ODQ, and EHNA. We propose that the increase of basal ICa in guinea pig cardiomyocytes previously observed with L-NMMA depends on the removal of a tonic NO inhibition. This increase of ICa is mimicked by blocking at different steps the cGMP-cascade activated by NO, suggesting a NO-guanylate cyclase mechanism in the basal control of ventricular calcium current.
一氧化氮（NO）对心肌细胞中L型钙电流（ICa）的控制及钙处理的几种作用已被描述。已证明心肌细胞在不同条件下可表达所有类型的一氧化氮合酶（NOS），但NO在钙电流调节中的作用仍存在争议。此前，我们在豚鼠心室细胞中已证明NOS抑制剂对ICa有刺激作用。在此，我们研究参与NO对心室细胞基础ICa假定抑制作用的细胞内机制。NOS抑制剂NG-单甲基-L-精氨酸（L-NMMA，1 mM）的刺激作用在钙瞬变测量中也存在，但仅在与L-精氨酸（L-arg，0.1 mM）预孵育后。在全细胞电压钳实验中，一氧化氮清除剂2-苯基-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物（PTIO，0.5 mM）以与NOS抑制剂类似的方式增加ICa峰值。同样，ODQ（1H-[1,2,4]恶二唑并[4,3-a]喹喔啉-1-酮，0.1 mM），一种NO靶标可溶性鸟苷酸环化酶的特异性抑制剂，也能够刺激ICa。EHNA（赤藓红-9-[2-羟基-3-壬基]腺嘌呤，30 microM）对II型磷酸二酯酶（cGMP激活型）的阻断对ICa产生了与PTIO和ODQ类似的作用。卡巴胆碱（CCh，1 microM）能够逆转PTIO、ODQ和EHNA对ICa的刺激作用。我们提出，先前用L-NMMA观察到的豚鼠心肌细胞基础ICa增加取决于对持续性NO抑制的消除。通过在不同步骤阻断由NO激活的cGMP级联反应可模拟这种ICa增加，提示在心室钙电流基础控制中存在NO-鸟苷酸环化酶机制。
