The genetic locus for incomplete congenital stationary night blindness
(CSNB2) has been identified as the CACNA1f gene, encoding the
α1F calcium channel subunit, a member of the L-type family
of calcium channels. The electroretinogram associated with CSNB2
implicates α1F in synaptic transmission between retinal
photoreceptors and bipolar cells. Using a recently developed monoclonal
antibody to α1F, we localize the channel to ribbon active
zones in rod photoreceptor terminals of the mouse retina, supporting a
role for α1F in mediating glutamate release from rods.
Detergent extraction experiments indicate that α1F is part
of a detergent-resistant active zone complex, which also includes the
synaptic ribbons. Comparison of native mouse rod calcium currents with
recombinant α1F currents reveals that the
current–voltage relationship for the native current is shifted
approximately 30 mV to more hyperpolarized potentials than for the
recombinant α1F current, suggesting modulation of the
native channel by intracellular factors. Lastly, we present evidence for
L-type α1D calcium channel subunits in cone terminals of
the mouse retina. The presence of α1D channels in cones may
explain the residual visual abilities of individuals with CSNB2.