Using the frog bladder model system we have explored the effects of different physical variables and factors that affect the regulation of structure and permeability of tight junctions. We have determined that isoforms of the PKC and the G protein family.are directly associated with the junctional region where they co-localize with the ZO-1 protein and have a marked effect on tight junction reassembly and permeability. Using the bladder epithelium model system we have also showed that tight junction permeability changes in response to applied clamping potential, depending on the CA++ concentration in the apical solution and the value and polarity of the camping potential. Assuming that the permeability properties of the tight junction strand are based on the summation of the conductance properties of each one of its monomers we estimated that the unitary values of conductance of each subunit would be in the range of 10-4 to 10-3 pS. These values of conductance are three orders of magnitude lower that the conductance of membrane ion channels and would not explain how tight junctions allow the passage of large molecules like sucrose and certain dyes. Alternatively, we are now proposing that tight junction permeability is based on higher conductance channels that are intercalated in the strand structure. This model could also explain how tight junction permeability can be regulated independent of changes in the structure of the strand. As a preliminary step for the identification and characterization of organ of Corti specific members of the cadherin protein family we obtained cDNA fragments encoding for E-cadherin, N-cadherin and P-cadherin selectively amplified by PCR. We have also screened an organ of Corti cDNA library with a cadherin-conserved probe and identified an E-cadherin clone having an alternative spliced 3'UTR.
