Gap junctional coupling in lenses lacking alpha-3 connexin

Fiber cells of the lens are interconnected by an extensive network of gap junctions containing [[Alpha].sub.3] (Cx46) and [[Alpha].sub.8] (Cx50) connexins. A specific role for these connexins in lens homeostasis is not known. To determine the contribution of these connexins to lens function, we used impedance techniques to study cell-to-cell coupling in lenses from homozygous [[Alpha].sub.3] knockout (-/-), heterozygous (+/-), and wild-type (+/+) mice. Western blots and immunofluorescence data indicated that [[Alpha].sub.8] remained at similar levels in the three classes of lenses, whereas [[Alpha].sub.3] was approximately 50% of the normal level in the +/- lenses, and it was absent from the -/- lenses. Moreover, the data from +/+ lenses suggest that a cleavage of connexins occurs abruptly between the peripheral shell of differentiating fibers (DF) and the inner core of mature fibers (MF). The appearance of the cleaved connexins was correlated to a change in the coupling conductance. In -/- lenses the coupling conductance of MF was zero, and these fibers were depolarized by about 30 mV from normal ([approximately equal to]-65 mV). The DF remained coupled, but the conductance was reduced to 30-35% of normal. However, the gap junctions in the DF of [[Alpha].sub.3] -/- lenses remained sensitive to pH. We conclude that [[Alpha].sub.3] connexin is necessary for the coupling of central fibers to peripheral cells, and that this coupling is essential for fiber cell homeostasis because uncoupled MF depolarize and subsequently become opaque.