Connexin 43 is the most ubiquitous connexin in the human body and is one of 20 known vertebrate connexins. Specific mutations (17 in total) of Cx43 are associated with a form of dental dysplasia occurring as an autosomal dominant disorder. This disorder manifests itself in the form of digit malformation and neurological degeneration. One in a million individuals in the USA population has this disorder. The multigene family for connexins encodes for the gap junction channel which allows for intercellular communication in the form of exchange of various molecules and ions. We have studied the properties of a specific mutated form of (rat) Cx43 (Q49K), measuring its conductivity and permeability. We transfected this mutant in HeLa cells both transiently and stably. Western blot analysis was run on cells transfected with either wild type Cx43 or mutant Q49K and RIN cells (connexin deficient) to probe for Cx43. Transfected cells were exposed to electrophysiological studies to measure conductance. Experiments were performed using single and double whole cell patching clamp methodology. The voltage dependence of the mutant was identical to wild type Cx43 and steady state macroscopic junctional conductance was the same for wild type and mutant. Dye injection analysis was also performed and showed variance in permeability. Data from these studies indicated that the specific mutation we have studied in the Cx43 gene does not affect synthesis or trafficking to membrane or voltage dependence but does affect the permeability of the channel. Thus permeability becomes the most relevant suspect parameter as a potential causal factor in dental dysplasia. This study was supported by funding from the Department of Physiology and Biophysics.