Retinal bipolar cell types differ in their inventory of ion channels.

Bipolar cells were recorded in rat retinal slices to study the distribution of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels. Patch-clamp whole cell measurements were combined with intracellular filling and recorded cells were morphologically identified. HCN channel isoforms HCN1-4 are differentially expressed in bipolar cells. Each bipolar cell type has a characteristic inventory of HCN channels. The combination of HCN channel currents and other voltage-gated currents can be used as a kind of "finger print" to electrophysiologically identify and classify bipolar cell types. Using this approach of combined electrophysiological and morphological classification we could identify a new ON-cone bipolar cell type.