GABA neurotransmitter signaling in the developing mouse lens: dynamic regulation of components and functionality.

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the vertebrate nervous system, serves as a signaling molecule modulating diverse processes during embryonic development. Earlier we have demonstrated that different forms of glutamic acid decarboxylase (GAD) are differentially regulated during mouse lens development. Here we show that the developing lens expresses also components of GABA signaling downstream of GAD. Multiple GABA(A) and GABA(B) receptor subunits as well as the GABA transporters show expression profiles highly correlated with the expression of different GADs. GABA receptors (GABAR) and the vesicular GABA transporter localize at the apical/basal membranes of the lens epithelia and differentiating fibers and may be involved in conventional GABAR-mediated signaling, while the membrane GABA transporters may also function as Na(+)/Cl(-)/GABA carriers. The functionality of GABAR was verified by calcium imaging in whole lenses. Our data suggest that GABA synthesized locally by GAD, acts through GABA receptors by modulating the intracellular calcium levels.