Voltage-activated Ca2+ channels play an
important role in synaptic transmission, signal
processing and development. The immunohistochemical
localization of Cav1.2 (a1C) and Cav2.3 (a1E) Ca2+
channels was studied in the developing and adult mouse
organ of Corti using subunit-specific antibodies and
fluorescent secondary antibodies with cochlear
cryosections. Cav1.2 immunoreactivity has been
detected from postnatal day 14 (P14) onwards at the
synapses between cholinergic medial efferents and outer
hair cells as revealed by co-staining with antisynaptophysin
and anti-choline acetyltransferase. Most
likely the Cav1.2 immunoreactivity was located
presynaptically at the site of contact of the efferent
bouton with the outer hair cell which suggests a role for
class C L-type Ca2+ channels in synaptic transmission of
the medial efferent system. The localization of the
second Ca2+ channel tested, Cav2.3, showed a
pronounced change during cochlear development. From
P2 until P10, Cav2.3 immunoreactivity was found in the
outer spiral bundle followed by the inner spiral bundle,
efferent endings and by medial efferent fibers. Around
P14, Cav2.3 immunoreactivity disappeared from these
structures and from P19 onwards it was observed in the
basal poles of the outer hair cell membranes