Recent studies on the lens implicate changes in gap junctions with development of cataracts. Gap junctions are the structures between individual lens cells which appear to allow passage of nutrients in the absence of vascularization. Regulation of these communicating channels could restrict the spread of injury as well as maintain tissue homeostasis. Toward the goal of understanding this regulation, we have reconstituted lens membranes in a novel spherical model membrane system. Voltage-dependent spontaneous steps in conductance across the contact region between two membranes suggest formation of junctional complexes and opening and closing of single channels. Our preliminary data show a linear inhibition of conductance by voltage from 100 pS at O mV to zero conductance at 60 mV in 0.14 M KCl. In this proposal, lens membranes containing gap junction proteins will continue to be supplied by Dr. Lawrence Takemoto (Kansas State University). Conductance changes will be analyzed as a function of time and applied transmembrane electrical potential. Modulation of junction formation will be investigated by varying pH and Ca++. In order to specifically identify the lens major intrinsic protein (MIP, Mr 26,000) as the one responsible for junction formation, inhibition of conductance will be tested with antibodies of predetermined specificity. The purified MIP will also be tested for reconstitution of junctional conductance. Regulation of lens gap junction permeability will be similarly compared to that of liver and heart. Thus, in the absence of complicating cellular metabolism, we will characterize the functional regulation of gap junction permeability.
