Bratz Ian N, Swafford Albert N, Kanagy Nancy L, Dick Gregory M
Department of Physiology, LSU Health Sciences Center, 1901 Perdido St., New Orleans, LA 70112, USA.
Am J Physiol Heart Circ Physiol. 2005 Sep;289(3):H1284-90. doi: 10.1152/ajpheart.01053.2004. Epub 2005 May 6.
Smooth muscle membrane potential is determined, in part, by K(+) channels. In the companion paper to this article, we demonstrated that superior mesenteric arteries from rats made hypertensive with N(omega)-nitro-l-arginine (l-NNA) are depolarized and express less K(+) channel protein compared with those from normotensive rats. In the present study, we used patch-clamp techniques to test the hypothesis that l-NNA-induced hypertension reduces the functional expression of K(+) channels in smooth muscle. In whole cell experiments using a Ca(2+)-free pipette solution, current at 0 mV, largely due to voltage-dependent K(+) (K(V)) channels, was reduced approximately 60% by hypertension (2.7 +/- 0.4 vs. 1.1 +/- 0.2 pA/pF). Current at +100 mV with 300 nM free Ca(2+), largely due to large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels, was reduced approximately 40% by hypertension (181 +/- 24 vs. 101 +/- 28 pA/pF). Current blocked by 3 mM 4-aminopyridine, an inhibitor of many K(V) channel types, was reduced approximately 50% by hypertension (1.0 +/- 0.4 vs. 0.5 +/- 0.2 pA/pF). Current blocked by 1 mM tetraethylammonium, an inhibitor of BK(Ca) channels, was reduced approximately 40% by hypertension (86 +/- 14 vs. 53 +/- 19 pA/pF). Differences in BK(Ca) current magnitude are not attributable to changes in single-channel conductance or Ca(2+)/voltage sensitivity. The data support the hypothesis that l-NNA-induced hypertension reduces K(+) current in vascular smooth muscle. Reduced molecular and functional expression of K(+) channels may partly explain the depolarization and augmented contractile sensitivity of smooth muscle from l-NNA-treated rats.
平滑肌膜电位部分由钾离子通道决定。在本文的配套论文中，我们证明，与正常血压大鼠的肠系膜上动脉相比，用N（ω）-硝基-L-精氨酸（L-NNA）诱导高血压的大鼠的肠系膜上动脉发生去极化，且表达的钾离子通道蛋白较少。在本研究中，我们使用膜片钳技术来检验L-NNA诱导的高血压会降低平滑肌中钾离子通道功能表达这一假说。在使用无钙移液管溶液的全细胞实验中，0 mV时的电流主要归因于电压依赖性钾离子（K（V））通道，高血压使其降低了约60%（2.7±0.4对1.1±0.2 pA/pF）。在300 nM游离钙存在下，+100 mV时的电流主要归因于大电导钙激活钾离子（BK（Ca））通道，高血压使其降低了约40%（181±24对101±28 pA/pF）。许多类型的K（V）通道的抑制剂3 mM 4-氨基吡啶所阻断的电流，高血压使其降低了约50%（1.0±0.4对0.5±0.2 pA/pF）。BK（Ca）通道的抑制剂1 mM四乙铵所阻断的电流，高血压使其降低了约40%（86±14对53±19 pA/pF）。BK（Ca）电流大小的差异并非归因于单通道电导或钙/电压敏感性的变化。这些数据支持L-NNA诱导的高血压会降低血管平滑肌中钾离子电流这一假说。钾离子通道分子和功能表达的降低可能部分解释了L-NNA处理大鼠平滑肌的去极化和收缩敏感性增强。
