Localization of Rod Bipolar Cells in the Mammalian Retina Using an Antibody Against the α₁c L-type Ca²⁺ Channel

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Bipolar cells transmit stimuli via graded changes in membrane potential and neurotransmitter release is modulated by Ca²⁺ influx through L-type Ca²⁺ channels. The purpose of this study was to determine whether the α₁c subunit of L-type voltage-gated Ca²⁺ channel (α₁c L-type Ca²⁺ channel) colocalizes with protein kinase C alpha (PKC-α), which labels rod bipolar cells. Retinal whole mounts and vertical sections from mouse, hamster, rabbit, and dog were immunolabeled with antibodies against PKC-α and α₁c L-type Ca²⁺ channel, using fluorescein isothiocyanate (FITC) and Cy5 as visualizing agents. PKC-α-immunoreactive cells were morphologically identical to rod bipolar cells as previously reported. Their cell bodies were located within the inner nuclear layer, dendritic processes branched into the outer plexiform layer, and axons extended into the inner plexiform layer. Immunostaining showed that α₁c L-type Ca²⁺ channel colocalized with PKC-α in rod bipolar cells. The identical expression of PKC-α and α₁c L-type Ca²⁺ channel indicates that the α₁c L-‍type Ca²⁺ channel has a specific role in rod bipolar cells, and the antibody against the α₁c L-type Ca²⁺ channel may be a useful marker for studying the distribution of rod bipolar cells in mouse, hamster, rabbit, and dog retinas.