Berger M G, Vandier C, Bonnet P, Jackson W F, Rusch N J
Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USA.
Am J Physiol. 1998 Oct;275(4):H1351-9. doi: 10.1152/ajpheart.1998.275.4.H1351.
Decreases in intracellular pH (pHi) potently dilate coronary resistance arteries but constrict small pulmonary arteries. To define the ionic mechanisms of these responses, this study investigated whether acute decreases in pHi differentially regulate K+ currents in single vascular smooth muscle (VSM) cells isolated from rat coronary and pulmonary resistance arteries. In patch-clamp studies, whole cell K+ currents were elicited by 10-mV depolarizing steps between -60 and 0 mV in VSM cells obtained from 50- to 150-micrometers-OD arterial branches, and pHi was lowered by altering the NH4Cl gradient across the cell membrane. Progressively lowering pHi from calculated values of 7.0 to 6.7 and 6.4 increased the peak amplitude of K+ current in coronary VSM cells by 15 +/- 5 and 23 +/- 3% but reduced K+ current in pulmonary VSM cells by 18 +/- 3 and 21 +/- 3%, respectively. These changes were reversed by returning cells to the control pHi of 7.0 and were eliminated by dialyzing cells with pipette solution containing 50 mmol/l HEPES to buffer NH4Cl-induced changes in pHi. Pharmacological block of ATP-sensitive K+ channels and Ca2+-activated K+ channels by 1 micromol/l glibenclamide and 100 nmol/l iberiotoxin, respectively, did not prevent changes in K+ current levels induced by acidotic pHi. However, block of voltage-gated K+ channels by 3 mmol/l 4-aminopyridine abolished acidosis-induced changes in K+ current amplitudes in both VSM cell types. Interestingly, alpha-dendrotoxin (100 nmol/l), which blocks only select subtypes of voltage-gated K+ channels, abolished the acidosis-induced decrease in K+ current in pulmonary VSM cells but did not affect the acidosis-induced increase in K+ current observed in coronary VSM cells. These findings suggest that opposing, tissue-specific effects of pHi on distinct subtypes of voltage-gated K+ channels in coronary and pulmonary VSM membranes may differentially regulate vascular reactivity in these two circulations under conditions of acidotic stress.
细胞内pH值（pHi）降低会使冠状动脉阻力血管显著扩张，但会使肺小动脉收缩。为了明确这些反应的离子机制，本研究调查了pHi的急性降低是否会对从大鼠冠状动脉和肺阻力动脉分离出的单个血管平滑肌（VSM）细胞中的钾离子电流产生不同调节作用。在膜片钳研究中，从外径为50至150微米的动脉分支获取的VSM细胞，通过在-60至0 mV之间进行10 mV的去极化步阶来诱发全细胞钾离子电流，通过改变跨细胞膜的氯化铵梯度来降低pHi。将pHi从计算值7.0逐步降至6.7和6.4，会使冠状动脉VSM细胞中钾离子电流的峰值幅度分别增加15±5%和23±3%，但会使肺VSM细胞中的钾离子电流分别降低18±3%和21±3%。通过将细胞恢复到7.0的对照pHi，这些变化得以逆转，并且通过用含有50 mmol/L HEPES的移液管溶液透析细胞以缓冲氯化铵诱导的pHi变化，这些变化被消除。分别用1 μmol/L格列本脲和100 nmol/L埃博霉素对ATP敏感性钾通道和钙激活钾通道进行药理学阻断，并未阻止酸中毒性pHi诱导的钾离子电流水平变化。然而，用3 mmol/L 4-氨基吡啶阻断电压门控钾通道消除了两种VSM细胞类型中酸中毒诱导的钾离子电流幅度变化。有趣的是，仅阻断特定亚型电压门控钾通道的α-树眼镜蛇毒素（100 nmol/L）消除了酸中毒诱导的肺VSM细胞中钾离子电流的降低，但并未影响在冠状动脉VSM细胞中观察到的酸中毒诱导的钾离子电流增加。这些发现表明，在酸中毒应激条件下，pHi对冠状动脉和肺VSM膜中不同亚型电压门控钾通道的相反的、组织特异性作用可能会对这两个循环中的血管反应性产生不同调节。
