Dresviannikov A V, Bolton T B, Zholos A V
Department of Nerve-Muscle Physiology, Laboratory of Molecular Pharmacology of Cellular Receptors and Ion Channels, Bogomoletz Institute of Physiology, Kiev, Ukraine.
Br J Pharmacol. 2006 Sep;149(2):179-87. doi: 10.1038/sj.bjp.0706852. Epub 2006 Aug 7.
There is little information about the excitatory cholinergic mechanisms of mouse small intestine although this model is important for gene knock-out studies.
Using patch-clamp techniques, voltage-dependent and pharmacological properties of carbachol- or intracellular GTPgammaS-activated cationic channels in mouse ileal myocytes were investigated.
Three types of cation channels were identified in outside-out patches (17, 70 and 140 pS). The voltage-dependent behaviour of the 70 pS channel, which was also the most abundantly expressed channel (approximately 0.35 micro(-2)) was most consistent with the properties of the whole-cell muscarinic current (half-maximal activation at -72.3+/-9.3 mV, slope of -9.1+/-7.4 mV and mean open probability of 0.16+/-0.01 at -40 mV; at near maximal activation by 50 microM carbachol). Both channel conductance and open probability depended on the permeant cation in the order: Cs+ (70 pS) >Rb+ (66pS) >Na+ (47 pS) >Li+ (30 pS). External application of divalent cations, quinine, SK&F 96365 or La3+ strongly inhibited the whole-cell current. At the single channel level the nature of the inhibitory effects appeared to be very different. Either reduction of the open probability (quinine and to some extent SK&F 96365 and La3+) or of unitary current amplitude (Ca2+, Mg2+, SK&F 96365, La3+) was observed implying significant differences in the dissociation rates of the blockers.
The muscarinic cation current of murine small intestine is very similar to that in guinea-pig myocytes and murine genetic manipulation should yield important information about muscarinic receptor transduction mechanisms.
尽管小鼠小肠模型对于基因敲除研究很重要，但关于其兴奋性胆碱能机制的信息却很少。
采用膜片钳技术，研究了小鼠回肠肌细胞中卡巴胆碱或细胞内GTPγS激活的阳离子通道的电压依赖性和药理学特性。
在外侧向外式膜片中鉴定出三种类型的阳离子通道（17、70和140 pS）。70 pS通道的电压依赖性行为，也是表达最丰富的通道（约0.35个/微米²），与全细胞膜毒蕈碱电流的特性最为一致（在-72.3±9.3 mV时半最大激活，斜率为-9.1±7.4 mV，在-40 mV时平均开放概率为0.16±0.01；在50微摩尔卡巴胆碱接近最大激活时）。通道电导和开放概率均取决于通透阳离子，顺序为：Cs⁺（70 pS）＞Rb⁺（66 pS）＞Na⁺（47 pS）＞Li⁺（30 pS）。外部施加二价阳离子、奎宁、SK&F 96365或La³⁺强烈抑制全细胞电流。在单通道水平上，抑制作用的性质似乎非常不同。观察到要么开放概率降低（奎宁以及在一定程度上SK&F 96365和La³⁺），要么单位电流幅度降低（Ca²⁺、Mg²⁺、SK&F 96365、La³⁺），这意味着阻滞剂的解离速率存在显著差异。
小鼠小肠的毒蕈碱阳离子电流与豚鼠肌细胞中的非常相似，小鼠基因操作应能产生有关毒蕈碱受体转导机制的重要信息。
