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Theresa Puthussery, Jacqueline Gayet, William Taylor; CaV3.1 (T-Type) Calcium Channels in Bipolar Cells of the Macaque Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6158.
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The functional properties of bipolar cells are shaped by the inventory and sub-cellular distribution of voltage-gated ion channels they express. Here, we examine the localization and functional expression of the T-type calcium channel subunit, CaV3.1, in bipolar cells of the macaque monkey retina.
Macaque eyes were obtained under the Tissue Distribution Program of the Oregon National Primate Research Center. For electrophysiology, whole-cell voltage-clamp and current-clamp recordings were made from bipolar cells in a light-adapted retinal slice preparation. For immunohistochemistry, paraformaldehyde fixed retinal sections were immunolabelled for CaV3.1 (Neuromab) in combination with subtype-specific bipolar cell markers.
Depolarizing voltage steps from a holding potential of -90mV, revealed transient, mibefradil-sensitive, inward currents in cells that had morphological features consistent with DB2, DB4 and DB5 bipolar cells. In contrast, DB1, DB6 and midget bipolar cells lacked T-type currents. DB3 bipolar cells comprised two functionally distinct groups; one type, which we denote as DB3a, expressed large voltage-gated sodium currents but lacked T-type calcium currents, while a second type, which we denote as DB3b, exhibited large T-type calcium currents but lacked sodium currents. T-type currents remained in cells in which the axon terminal system had been removed, suggesting localization of channels in the somatic and/or dendritic compartments. Current-clamp recordings showed that T-type channels produce calcium spikes in response to depolarizing current injection. Immunohistochemistry for the T-type calcium channel subunit, CaV3.1, revealed expression in the somatodendritic compartment of the same bipolar cell types that exhibited T-type currents by electrophysiology.
These data demonstrate the presence of CaV3.1-mediated currents in sub-types of primate bipolar cells. We propose that these channels serve to boost signaling within transient visual pathways.
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