REGULATION OF MEMBRANE POTENTIAL IN COLONIC MYOCYTES

在上一个资助期间，我们发现主要的肠内神经递质通过控制膜电位间接调节CA2+通道的开放概率和CA2+内流。一般来说，兴奋性递质通过激活非选择性阳离子电流引起去极化，抑制性递质激活K+电导引起超极化和兴奋性降低。我们将研究几种新的K+电导引起超极化和降低兴奋性。我们将研究几种新的K+电导，这些电导参与了膜电位的设置和节律性的调节。我们最近发现，结肠肌肉表达了几类内向整流电导（Kir），我们将研究这些通道的每一类如何促进电活动。Ba2+敏感电流（可能是由于Kir2.1通道的表达）似乎有助于膜电位。Kir 3基因也有表达，该家族成员的表达所产生的电导可以帮助维持兴奋激动剂反应期间电活动的相性。Kir6转录本也被鉴定出来，这些通道与磺酰脲受体蛋白亚基（SUR 2B）结合可能在结肠肌肉中形成K/ATP通道。由此产生的电导似乎有助于静息膜电位，并可能被激动剂进一步激活。我们还将研究小电导Ca/2+激活的K+通道如何被调节并参与肠抑制性神经反应，我们将研究快速失活的电压依赖性K+电导如何影响平滑肌兴奋性和对起搏器活动的反应。我们还将研究Ca2+激活的Cl-电流如何被激活并有助于对神经递质的反应。我们最近发现了在结肠肌肉中表达拉伸激活的Cl-传导的证据。由这种电导产生的电流将被表征，我们将试图确定这种电导如何促进完整肌肉对拉伸的反应。最后，我们将研究磷酸化对结肠肌肉中Ca2+电流的影响，并确定这种传导是如何由神经递质和激素直接调节的机制。这些研究将极大地扩展我们对设置膜电位和调节结肠肌肉兴奋性的基本离子机制的理解。

During the last funding period we found that the major enteric neurotransmitters regulate the open probability of CA2+ channels and Ca2+ influx indirectly, by controlling membrane potential. In general excitatory transmitters cause depolarization by activation of non- selective cation currents and inhibitory transmitters activate K+ conductances to cause hyperpolarization and reduced excitability. We will investigate several novel K+ conductances to cause hyperpolarization and reduced excitability. We will investigate several novel K+ conductances that are involved in setting membrane potential and regulation rhythmicity. We have found recently that several families of inward rectifier conductances (Kir) are expressed by colonic muscles, and we will investigate how each class of these channels contributes to electrical activity. Ba2+ - sensitive current (possibly due to expression of Kir2.1 channels) appear to contribute to membrane potential. Kir 3 genes are also expressed, and the conductance resulting from expression of members of this family could help sustain the phasic nature of electrical activity during responses to excitatory agonists. Kir6 transcripts have also been identified, and these channels, in combination with sulfonylurea receptor protein subunits (SUR 2B) may form K/ATP channels in colonic muscles. The resulting conductance appears to contribute to resting membrane potential and may be activated further by agonists. We will also study how small conductance Ca/2+ - activated K+ channels are regulated and participate in enteric inhibitory neural responses, and we will investigate how rapidly inactivating, voltage-dependent K+ conductances affect smooth muscle excitability and responses to pacemaker activity. We will also study how Ca2+-activated Cl- currents are activated and contribute to responses to neurotransmitters. We have recently found evidence for expression of a stretch-activated Cl- conductance in colonic muscles. Currents resulting from this conductance will be characterized, and we will attempt to determine how this conductance contributes to the response of intact muscle to stretch. Finally, we will study the effects of phosphorylation on Ca2+ currents in colonic muscles and determine how the mechanisms by which this conductance is directly regulated by neurotransmitters and hormones. These studies will greatly expand our understanding of the basic ion mechanisms that set membrane potential and regulate excitability in colonic muscles.