Joint Study on the Molecular Biology of SA Channels

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Stretch activated (SA) ion channels are expressed in many types of cells and supposed to play an important role in fundamental cell functions including cell growth, division, morphogenesis, and volume regulation. However, because of the lack of information on their molecular structure, further exploration of SA channels is confronted with difficulties. Very recently a gene encoding an SA channel has been isolated from E.coli, however, its shows a peculiar sequence devoid of any homology with known sequences of ion channels in eucaryotic cels. The aim of the present study was to find SA channel genes from eucaryotic cells and to develop a specific blockers to the SA channel, by which we could explore structure-function and physiological roles of SA channels. We found a candidate gene in MDCK cells of which sequence has a significant homology with mec gene that is supposed to be a putative SA channel gene. We also found, in Drosophila, a gene encoding new type of cGMP gated ion channel that may contribute to mechanotransduction in this species. Expression and functional assay of these genes are in progress. A certain spider venom has been found to include peptides that specifically block the SA channel. We succeeded in purifying some of these peptides with defferent degree of affinity to the SA channel. The structure of a low a affinity one has been sccessfully determined. Determination of a high affinity one is now in progress. We are planning to prepare an affinity column by using the peptide to purify SA channel proteins. We are also going to prepare a fluorescent-conjugated peptide by which the distribution of SA channels on the cell surface could be studied.