STUDY ON THE DEVELOPMENT OF MOLECULAR BIOLOGY AND PHYSIOLOGY OF SA CHANNELS

牵张激活（SA）通道在多种细胞中表达，并且被认为在基本细胞功能中具有重要作用。但其生理功能尚不清楚，除E.杆菌解决这些问题是SA信道的首要问题。本研究课题的目的是通过日美合作，找到实现这一目标的线索。关于第一个问题，通过测定细胞内Ca 2+的增加量，推测SA通道的全细胞活性，发现阳离子选择性SA通道在A6细胞的调节性容积减少中发挥重要作用。此外，阳离子选择性SA通道在内皮细胞牵张诱导的细胞重塑中的作用已得到阐明（日本方面）。另一方面，美国研究人员开发了一种利用原子力显微镜（AFM）的杠杆对培养细胞施加定量机械刺激的方法。他们用这种方法结合SA通道电流的同步全细胞记录成功地解释了牵张诱导的心脏细胞活动。第二个问题是一个难题。我们试图从果蝇中克隆一个与mec基因同源的SA通道基因，但没有成功。美国方面试图从蜘蛛毒液中纯化SA通道特异性阻断剂，但尚未完成。然而，在最后一刻，我们（日本方面）可以从酵母中鉴定出编码阳离子选择性SA通道的基因（mid-1）。这是第一个确定的阳离子选择性SA通道的基因。通过这一发现，我们可以预见各种有趣的研究项目，包括结构-功能研究。基于这一结果，我们将进一步推动日本和美国之间的合作。

Stretch activated (SA) channels are expressed in a variety of cells and, thought to have important roles in fundamental cell functions. However their physiological functions are not yet known and their molecular entity has not yet be identified except for that in e. coli. To resolve these problems is the most important issue on the SA channel. The aim of this research project is to find out a clue to this goal through a collaboration between Japan and the U.S.As for the first problem, a cation selective SA channel has been found to have an important role in the regulatory volume decrease in A6 cells throuigh the estimation of whole cell activity of the SA channel by measuring intracellular Ca2+ incresae. Moreover the role of a cation selective SA channel has been clarified in stretch -induced cell remodeling in endothelial cells (Japan side). On the other hand ; the US researchers has developed a method to apply quantitative mechanical stimuli to cultured cells using canti-lever of AFM (atomic force microscope). They successfully explained the stretch induced-activity of heart cells by this method combined with sinultaneous whole cell recordings of SA channel currents.The second problem has been a tough one. We tried to clone a Drosophila gene homologous to mec gene from c.elegance, a putative SA channel gene, but failed. The US side tried to purify a SA channel-specific blocker from spider venoms, but yet to be done. However, at the last moment, we (Japan side) could identify a gene (mid-1) encoding cation selective SA channel from yeast. This is the first identified gene for the cation selective SA channel. By this finding we can evisage a variety of intriguing research projects including structure-function study. Based on this result, we will pursue further collaboration between Japan and the US.