Chemoreception in Paramecium

从刺激中获取能量并在神经系统中启动反应信号的过程称为感觉转导。在包括味觉和嗅觉在内的化学感觉通路中，化学刺激剂分子通常通过与感觉细胞膜上高度特异的受体结合来发挥作用。这种结合在某种程度上与启动电信号的膜的特性变化相耦合。很可能在许多情况下，转导过程涉及内部信使分子或离子，如环核苷酸、钙或脂质代谢物。微小的水生单细胞生物草履虫表现出简单的化学传感行为，具有许多有趣的突变菌株，其细胞膜具有几个类似于兴奋性神经细胞的特性。这是一个非常成功的模型系统，用于澄清化学感官接受的某些方面。本项目将探索草履虫中化学感受器的结构、功能和分布，以及它们如何在转导过程中与体内钙水平相互作用。其中一个重要的刺激分子是环核苷酸化合物cAMP，它与众所周知的具有重要代谢功能的三磷酸腺苷密切相关。分子遗传学将被用于克隆和测序作为cAMP结合受体位置的膜蛋白的基因。一旦预测了基因序列，就会产生针对该基因内较短肽序列的抗体来探测受体的结构和分布，并预测受体分子的功能域。钙水平将使用染料测量，正常和突变菌株将被用来表征由三磷酸腺苷驱动的“分子泵”的性质，该分子泵分泌钙。这个新的模型系统的发现将对化学感觉工作产生相当大的影响，因为很少有化学感觉受体被表征，而且还没有出现共同的模式。这一结果，以及有关钙泵的结果，可能对神经科学家来说也很重要，因为其中许多机制可能与神经元之间正常运作的突触接触中发现的机制相似。

The capture of energy from a stimulus and the initiation of a response signal in the nervous system is termed sensory transduction. In the chemosensory pathways, including taste and smell, chemical stimulant molecules often act by binding to highly specific receptor sites on the membrane of the sensory cell. This binding is in some way coupled to a characteristic change in the membrane that initiates an electrical signal. It is likely that in many cases the transduction process involves internal messenger molecules or ions, such as cyclic nucleotides,calcium, or lipid metabolites. The microscopic aquatic single-celled organism Paramecium shows simple chemosensory behavior, has many interesting mutant strains, and its cell membrane has several properties similar to excitable nerve cells. It has been a very successful model system for clarifying some aspects of chemosensory reception. This project will explore the structure, function, and distribution of chemoreceptor sites in Paramecium, and how they interact with levels of internal calcium in the transduction process. One of the important stimulus molecules is a cyclic nucleotide compound, cAMP, closely related to the well-known ATP that has vital metabolic functions. Molecular genetics will be used to clone and sequence the gene for the membrane protein thatacts as the binding receptor site for cAMP. Once the gene sequence is predicted, antibodies to shorter peptide sequences within that gene will be made to probe receptor structure and distribution, and to predict the functional domains of the receptor molecule. Calcium levels will be measured using dyes, and normal and mutant strains will be used to characterize the nature of the "molecular pump" driven by ATP that extrudes calcium. Findings from this novel model system will have considerable impact on chemosensory work, because very few chemosensory receptors have yet been characterized, and no common patterns have emerged yet. The results, along with those on the calcium pump, are likely to be important also to neuroscientists in general, since many of the mechanisms may be similar to those found in the functioning synaptic contacts between neurons.