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

PURPOSE: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. METHODS: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. RESULTS:Large-terminal, ON-type bipolar cells express transcripts of Cav1.3a and/or Cav1.3b. CONCLUSIONS: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.

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