Identification of calcium channel alpha1 subunit mRNA expressed in retinal bipolar neurons

Glutamate release from goldfish bipolar cell terminals is driven by Ca2+ influx through L-type calcium channels that exhibit several uncommon features, including rapid kinetics of activation and deactivation, slow inactivation, and activation at an unusually negative voltage range for L-type channels. The purpose of this study was to establish the molecular identities of the alpha1 subunits responsible for these distinctive properties.

Transcripts for calcium channel alpha1 subunits expressed in individual goldfish ON-type bipolar cells were identified using single-cell reverse transcriptase polymerase chain reaction (RT-PCR). After cloning the goldfish homologs of the zebrafish and mammalian subunits, we designed sets of nested primers that are specific for Cav1.3a, and Cav1.3b L-type calcium channels.

Large-terminal, ON-type bipolar cells express transcripts of Cav1.3a and/or Cav1.3b.

The endogenous expression of only one or both subunits in a single cell raises the possibility of functionally distinct classes of bipolar cells that differ in calcium current properties.