Chung Seung-Soo, Ahn Duck-Sun, Lee Hong-Ghi, Lee Young-Ho, Nam Taick-Sang
Department of Physiology, College of Medicine, Yonsei University 134, Shinchon-Dong, Seodaemun-Gu, Seoul 120-752, Republic of Korea.
Exp Physiol. 2005 Jul;90(4):577-86. doi: 10.1113/expphysiol.2004.029611. Epub 2005 Apr 15.
The effect of sodium nitroprusside (SNP) on carbachol (CCh)-evoked inward cationic current (Icat) oscillations in guinea-pig ileal longitudinal myocytes was investigated using the whole-cell patch-clamp technique and permeabilized longitudinal muscle strips. SNP (10 microm) completely inhibited I(cat) oscillations evoked by 1 microm CCh. 1H-(1,2,4) Oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 1 microm) almost completely prevented the inhibitory effect of SNP on Icat oscillations. 8-Bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP; 30 microm) in the pipette solution completely abolished Icat oscillations. However, a pipette solution containing Rp-8-Br-cGMP (30 microm) almost completely abolished the inhibitory effect of SNP on Icat oscillations. When the intracellular calcium concentration ([Ca2+]i) was held at a resting level using BAPTA (10 mm) and Ca2+ (4.6 microm) in the pipette solution, CCh (1 microm) evoked only the sustained component of Icat without any oscillations and SNP did not affect the current. A high concentration of inositol 1,4,5-trisphosphate (IP3; 30 microm) in the patch pipette solutions significantly reduced the inhibitory effect of SNP (10 microm) on Icat oscillations. SNP significantly inhibited the Ca2+ release evoked by either CCh or IP3 but not by caffeine in permeabilized preparations of longitudinal muscle strips. These results suggest that the inhibitory effects of SNP on Icat oscillations are mediated, in part, by functional modulation of the IP3 receptor, and not by the inhibition of cationic channels themselves or by muscarinic receptors in the plasma membrane. This inhibition seems to be mediated by an increased cGMP concentration in a protein kinase G-dependent manner.
采用全细胞膜片钳技术和通透化的纵行肌条，研究了硝普钠（SNP）对豚鼠回肠纵行肌细胞中卡巴胆碱（CCh）诱发的内向阳离子电流（Icat）振荡的影响。SNP（10微摩尔）完全抑制了1微摩尔CCh诱发的Icat振荡。1H-（1,2,4）恶二唑[4,3-a]喹喔啉-1-酮（ODQ；1微摩尔）几乎完全阻止了SNP对Icat振荡的抑制作用。移液管溶液中的8-溴鸟苷3',5'-环一磷酸（8-Br-cGMP；30微摩尔）完全消除了Icat振荡。然而，含有Rp-8-Br-cGMP（30微摩尔）的移液管溶液几乎完全消除了SNP对Icat振荡的抑制作用。当使用移液管溶液中的BAPTA（10毫摩尔）和Ca2+（4.6微摩尔）将细胞内钙浓度（[Ca2+]i）维持在静息水平时，CCh（1微摩尔）仅诱发Icat的持续成分而无任何振荡，且SNP不影响该电流。膜片钳移液管溶液中高浓度的肌醇1,4,5-三磷酸（IP3；30微摩尔）显著降低了SNP（10微摩尔）对Icat振荡的抑制作用。在纵行肌条的通透化制剂中，SNP显著抑制了由CCh或IP3诱发的Ca2+释放，但不抑制咖啡因诱发的Ca2+释放。这些结果表明，SNP对Icat振荡的抑制作用部分是由IP3受体的功能调节介导的，而不是通过抑制阳离子通道本身或质膜中的毒蕈碱受体介导的。这种抑制似乎是以蛋白激酶G依赖的方式通过增加cGMP浓度介导的。
