ROLE OF THE SODIUM PUMP IN COLONIC MOTILITY

钠泵保持产生静息的离子梯度 在光滑的肌肉中具有潜力。因为Na+的交换 由于K+是非对称性的，泵是电生的，并有助于 膜电位。钠泵似乎特别重要。 因为高达35 mV的静息电位 归因于这种运输蛋白。之前的实验已经 显示环上的膜电位梯度为35 mV 犬结肠肌层，该层可被抑制 钠泵。这种梯度应该会极大地影响到 电慢波在环状肌肉中的传播，因为 定义梯度的势的范围是显著的 参与钙离子通道的电压依赖性失活 慢波。内流的钙离子减少会降低血管紧张素转换酶 细胞产生慢波，也会降低耦合 在慢波和收缩之间。此前的研究表明， 膜电位的梯度是由贡献的梯度引起的 钠泵的静息电势。有几个假说可以解释 泵浦电势的不均一性：i)泵浦的分子形式可以 在不同的细胞群体之间，休息在不同亲和力的 用于Na+或K+的泵.ii)泵密度(泵蛋白质量/单位面积 膜)可以通过圆形层不同。iii)衬底 浓度，如[Na+]i，来自不同地区的细胞 圆形层可能会有所不同，可能是由于钠渗透性的不同。 这项提案将严格地解决这些假设 电生理技术与现代分子技术的结合 技术首先，钠泵产生的实际电流将是 测量以确定在各种情况下泵的电镀能力 将对结肠肌肉的不同区域进行比较。分子实验将 通过测定mRNA来确定泵的异构体的分布和水平 和环状不同区域肌肉中多肽的丰度 一层。还计划进行一些实验来探索一些生理上的 调节泵基因表达的因子。建议数 实验将是第一个使用这种强大的技术来探索 钠泵在平滑肌肉中的作用，结果应该是 为未来对该蛋白质的研究提供了一个模型。

The sodium pump maintains the ionic gradients that generate resting potential in smooth muscles. Because the exchange of Na+ for K+ is non-symetrical, the pump is electrogenic and contributes to membrane potential. The sodium pump appears to be particularly important in colonic smooth muscle because up to 35 mV of the resting potential has been attributed to this transport protein. Previous experiments have demonstrated a 35 mV gradient in membrane potential across the circular layer in canine colonic muscles, which can be abolished by inhibition of the sodium pump. This gradient should greatly influence the generation and propagation of electrical slow waves in the circular muscle, because over the range of potentials the define the gradient there is significant voltage-dependent inactivation of the Ca2+ channels that participate in slow waves. A decrease in inward Ca2+ would decrease the ability of the cells to generate slow waves and would also tend to decrease the coupling between slow waves and contractions. Previous studies have suggested that the gradient in membrane potential is due to a gradient in the contribution of the sodium pump to resting potential. Several hypotheses might explain the heterogeneity in pump potential:i) The molecular from of the pump may differ between populations of cells, resting in different affinities of the pump for Na+ or K+.ii) Pump density (amount of pump protein/unit area of membrane) may differ through the circular layer.iii) Substrate concentration, such as [Na+]i, in cells from different regions of the circular layer may vary, perhaps due to differences in sodium permeability. This proposal will address these hypotheses with rigorous electrophysiological techniques in combination with modern molecular technology. First, the actual current generated by the sodium pump will be measured to determine in the electrogenic capability of the pump in various regions of colonic muscle will be compared. Molecular experiments will determine the distribution and levels of pump isoforms by measuring mRNA and polypeptide abundance in muscles from various regions of the circular layer. Experiments are also planned to explore some of the physiological factors which regulate genetic expression of the pump. The proposed experiments will be the first to use such powerful technology to explore the role of the sodium pump in smooth muscles, and the results should provide a model for future investigations of this protein.