Transfer of Metabolites through Lens Gap Junctions

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DESCRIPTION (provided by applicant): Lens cells require gap junction proteins to communicate with each other and develop properly. In particular, connexin43 (Cx43), Cx46, and Cx5O are needed for normal lens development and function. Knockout or mutations of genes encoding these connexins cause cataracts in mice and humans, respectively. Cx43, Cx46, and Cx5O form channels with different permeability characteristics. We hypothesize that transjunctional molecules needed for lens development pass through lens gap junctions, and that cataracts can result from an inability of cells to share these signals. We propose to identify and compare the transfer of endogenous metabolites that pass through these channels. This new research program will introduce a particularly innovative technological approach to investigate the role of gap junctions in the lens. In Specific Aim 1 we will determine the single channel size, total conductance, and number of functional gap junction channels expressed by mammalian cells transfected with connexins that are expressed in the lens. This will be done by standard dual voltage-clamp whole-cell recording methods. In Specific Aim 2 we will identify, quantitate, and compare the transfer of endogenous metabolites that pass through channels formed by connexins expressed in the lens. This will be accomplished with a novel strategy to identify and quantitate the transfer of endogenous molecules that pass through gap junctions between cells within a given time frame. Measurement will be taken at several time points to measure and compare the rates of transfer of specific metabolites through gap junction channels formed by Cx43, Cx46, and Cx5O. These results will be combined with data obtained from Aim 1 to calculate the permselectivity of these gap junctions to metabolites on a per channel basis. We hypothesize that lens connexins form channels that display selective permeabilities to specific metabolites, and that this connexin permselectivity can not be predicted solely on the basis of size and charge of the permeant. We will begin to identify the permeability characteristics and actual transjunctional molecules that are responsible for lens development, transparency, and disease. This work should lead to a greater understanding, and, ultimately, treatments, of eye diseases that result from aberrant gap junctional communication.