Gap junctional coupling in lenses lacking alpha(3) connexin

Fiber cells of the lens are interconnected by an extensive network of gap j unctions containing alpha(3) (Cx46) and as (Cx50) connexins. A specific rol e for these connexins in lens homeostasis is not known. To determine the co ntribution of these connexins to lens function, we used impedance technique s to study cell-to-cell coupling in lenses from homozygous alpha(3) knockou t (-/-), heterozygous (+/-), and wild-type (+/+) mice. Western blots and im munofluorescence data indicated that as remained at similar levels in the t hree classes of lenses, whereas alpha(3) was approximately 50% of the norma l level in the +/- lenses, and it was absent from the -/- lenses. Moreover, the data from +/- lenses suggest that a cleavage of connexins occurs abrup tly between the peripheral shell of differentiating fibers (DF) and the inn er core of mature fibers (MF), The appearance of the cleaved connexins was correlated to a change in the coupling conductance. In -/- lenses the coupl ing conductance of MF was zero, and these fibers were depolarized by about 30 mV from normal (approximate 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(3) -/- lenses remained sensitive to pH, We conclude that al pha(3) connexin is necessary for the coupling of central fibers to peripher al cells, and that this coupling is essential for fiber cell homeostasis be cause uncoupled MF depolarize and subsequently become opaque.