Hamilton K L, Meads L, Butt A G
Department of Physiology, School of Medical Sciences, University of Otago, Dunedin, New Zealand.
Pflugers Arch. 1999 Dec;439(1-2):158-66. doi: 10.1007/s004249900137.
We investigated the effects of 1-ethyl-2-benzimidazolinone (1-EBIO) on ion transport in the mouse jejunum through the use of the short-circuit (Isc) current technique and the application of the patch-clamp technique to isolated jejunal crypts. In HCO3- Ringer's, 1-EBIO stimulated a dose-dependent (EC50 964 micromol/l), bumetanide-sensitive increase in Isc consistent with stimulation of Cl- secretion. In contrast, in Cl(-)-free HCO3-Ringer's containing glucose, 1-EBIO (500 micromol/l) did not increase the phloridzin (100 micromol/l) sensitive Isc, suggesting that electrogenic Na+ absorption was unaltered. Measurement of the membrane potential (Vm) with the perforated-patch technique indicated that in isolated crypts, 1-EBIO caused a reversible hyperpolarization of Vm and an increase in the change in Vm associated with step changes in bath K+, consistent with an increase in K+ conductance. In on-cell patch experiments with KCI Ringer's in the patch pipette and crypts bathed with NaCl Ringer's, 1-EBIO (500 micromol/l) increased the open probability (NPo; 0.01+/-0.01 to 0.45+/-0.11, n=7) of an inwardly rectified intermediate conductance (g) channel. In inside-out patches with KCl Ringer's in the patch pipette and KCI Ringer's containing 100 nmol/l Ca2+ in the bath, the current-voltage relationship of the channel was inwardly rectified (g of 10 and 52 pS at -Vp of 100 and -100 mV, respectively) and reversed at 0 mV (n=5). Replacement of bath K+ with Na+ shifted the reversal potential toward the equilibrium potential for K+. In the presence of 1-EBIO, reducing the bath Ca2+ from 200 nmol/l to nominally Ca(2+)-free conditions decreased NPo from 0.90+/-0.27 to 0.07+/-0.03 (n=3). We conclude that in the mouse jejunum, I-EBIO does not stimulate electrogenic Na+ absorption. It does, however, stimulate secretion primarily through the activation of a basolateral, intermediate conductance Ca(2+)-sensitive K+ channel.
我们通过使用短路（Isc）电流技术以及将膜片钳技术应用于分离的空肠隐窝，研究了1-乙基-2-苯并咪唑啉酮（1-EBIO）对小鼠空肠离子转运的影响。在碳酸氢根林格氏液中，1-EBIO刺激Isc出现剂量依赖性（半数有效浓度为964微摩尔/升）、布美他尼敏感的增加，这与氯离子分泌的刺激一致。相比之下，在含葡萄糖的无氯碳酸氢根林格氏液中，1-EBIO（500微摩尔/升）并未增加根皮苷（100微摩尔/升）敏感的Isc，这表明电中性钠吸收未发生改变。用穿孔膜片技术测量膜电位（Vm）表明，在分离的隐窝中，1-EBIO导致Vm可逆性超极化，并使与浴液中钾离子阶跃变化相关的Vm变化增加，这与钾离子电导增加一致。在膜片吸管中使用氯化钾林格氏液且隐窝用氯化钠林格氏液灌注的细胞贴附膜片实验中，1-EBIO（500微摩尔/升）增加了内向整流型中电导（g）通道的开放概率（NPo；从0.01±0.01增加到0.4±0.11，n = 7）。在膜片吸管中使用氯化钾林格氏液且浴液中使用含100纳摩尔/升钙离子的氯化钾林格氏液的内面向外膜片中，该通道的电流-电压关系呈内向整流（在-100和-100毫伏的-Vp下，g分别为10和52皮安），且在0毫伏时反转（n = 5）。用钠离子替代浴液中的钾离子使反转电位向钾离子平衡电位移动。在存在1-EBIO的情况下，将浴液中的钙离子从200纳摩尔/升降低至名义上无钙离子的条件下，NPo从0.90±0.27降至0.07±0.03（n = 3）。我们得出结论，在小鼠空肠中，I-EBIO不刺激电中性钠吸收。然而，它主要通过激活基底外侧的中电导钙离子敏感钾通道来刺激分泌。
