Gap junctions provide a pathway for intercellular communication influencing tissue homeostasis. In the lens, gap junctions are particularly important for the maintenance of proper tissue functioning. The fiber cells, which constitute most of the lens tissue, are devoid of intracellular organelles and therefore most of the transport properties of the lens are located in the anterior epithelial cell layer. To exchange metabolites and maintain cellular volume the fiber cells depend heavily on the diffusional pathway created by gap junctions between lens fiber cells and between fiber and epithelial cells. Until recently intercellular communication in the lens was thought to be mediated by the main intrinsic protein of the lens (MIP), but evidence has been presented showing that MIP, although present in junctional areas, is not the gap junction forming protein. The applicant proposes to elucidate the role played by this ubiquitous protein in lens physiology by studying MIP channel properties in liposomes, bilayers, MIP transfected cells and in isolated fiber cells. Two newly identified proteins (M, 70 and 46 kD) are gap junction candidates, although there is at present no evidence that either protein forms gap junction channels. The applicant proposes to reconstitute MP70 into liposomes and planar bilayers and to transfect a communication deficient cell line with connexin46 cDNA to study their channel forming capacities. By comparing the properties of channels formed by these methods to those of the junctional membrane conductance between pairs of freshly dissociated lens fiber cells the applicant would be able to address the question of which protein(s) is(are) responsible for gap junction channel formation in the fiber cells. Through these studies the applicant expects to gain insights into the role of gap junctions and MIP channels in the homeostasis of lens tissue, and particularly into the possibility that disruption of function of these channels leads to pathological consequences.
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