Toronto Western Research Institute, University Health Network, 8th Floor, Main Pavillion Rm 327, 399 Bathurst Street, Toronto, Ontario M5T2S8, Canada.
World J Gastroenterol. 2010 Dec 14;16(46):5852-60. doi: 10.3748/wjg.v16.i46.5852.
To assess the effect of nitric oxide (NO) on the large conductance potassium channel (BK(Ca)) in isolated circular (CM) and sling (SM) muscle cells and muscle strips from the cat lower esophageal sphincter (LES) to determine its regulation of resting tone and relaxation.
Freshly enzymatically-digested and isolated circular smooth muscle cells were prepared from each LES region. To study outward K+ currents, the perforated patch clamp technique was employed. To assess LES resting tone and relaxation, muscle strips were mounted in perfused organ baths.
(1) Electrophysiological recordings from isolated cells: (a) CM was more depolarized than SM (-39.7 ± 0.8 mV vs -48.1 ± 1.6 mV, P < 0.001), and maximal outward current was similar (27.1 ± 1.5 pA/pF vs 25.7 ± 2.0 pA/pF, P > 0.05); (b) The NO donor sodium nitroprusside (SNP) increased outward currents only in CM (25.9 ± 1.9 to 46.7 ± 4.2 pA/pF, P < 0.001) but not SM (23.2 ± 3.1 to 27.0 ± 3.4 pA/pF, P > 0.05); (c) SNP added in the presence of the BK(Ca) antagonist iberiotoxin (IbTX) produced no increase in the outward current in CM (17.0 ± 2.8 vs 13.7 ± 2.2, P > 0.05); and (d) L-NNA caused a small insignificant inhibition of outward K+ currents in both muscles; and (2) Muscle strip studies: (a) Blockade of the nerves with tetrodotoxin (TTX), or BK(Ca) with IbTX had no significant effect on resting tone of either muscle; and (b) SNP reduced tone in both muscles, and was unaffected by the presence of TTX or IbTX.
Exogenous NO activates BK(Ca) only in CM of the cat. However, as opposed to other species, exogenous NO-induced relaxation is predominantly by a non-BK(Ca) mechanism, and endogenous NO has minimal effect on resting tone.
评估一氧化氮（NO）对猫食管下括约肌（LES）分离的环形（CM）和吊索（SM）肌细胞及肌条中大电导钙激活钾通道（BK（Ca））的影响，以确定其对静息张力和松弛的调节作用。
从每个 LES 区域新鲜酶解和分离的环形平滑肌细胞。为了研究外向钾电流，采用穿孔膜片钳技术。为了评估 LES 的静息张力和松弛，将肌条安装在灌注式器官浴中。
（1）分离细胞的电生理记录：（a）CM 比 SM 更去极化（-39.7 ± 0.8 mV 比-48.1 ± 1.6 mV，P < 0.001），最大外向电流相似（27.1 ± 1.5 pA/pF 比 25.7 ± 2.0 pA/pF，P > 0.05）；（b）NO 供体硝普钠（SNP）仅增加 CM 的外向电流（25.9 ± 1.9 至 46.7 ± 4.2 pA/pF，P < 0.001），而不增加 SM 的外向电流（23.2 ± 3.1 至 27.0 ± 3.4 pA/pF，P > 0.05）；（c）在 BK（Ca）拮抗剂 Iberiotoxin（IbTX）存在的情况下添加 SNP 并未增加 CM 中的外向电流（17.0 ± 2.8 比 13.7 ± 2.2，P > 0.05）；和（d）L-NNA 对两种肌肉的外向钾电流有轻微但无统计学意义的抑制作用；（2）肌条研究：（a）用河豚毒素（TTX）阻断神经或用 Iberiotoxin（IbTX）阻断 BK（Ca）对两种肌肉的静息张力均无显著影响；和（b）SNP 降低了两种肌肉的张力，并且不受 TTX 或 IbTX 的存在影响。
外源性 NO 仅在猫的 CM 中激活 BK（Ca）。然而，与其他物种不同的是，外源性 NO 诱导的松弛主要是通过非 BK（Ca）机制，而内源性 NO 对静息张力的影响很小。
