Molecular cloning and characterization of calcium channel alpha1 and beta subunits from tiger salamander retina

Voltage-gated Ca2+ channels are classified as high or low voltage-activated channels by their electrophysiological and pharmacological properties. L-type high voltage-activated Ca2+ channels are demonstrated to play an essential role in mediating sustained release of glutamate at ribbon synapses in both retinal photoreceptors and bipolar cells. In salamander retina, these L-type Ca2+ channels exhibit a high sensitivity to extracellular [H+] and [Cl−]. One channel and ion direct bonding mechanism has been proposed. A thorough examination of sequences and structural characteristics of this Ca2+ channel and its comparison against other previously cloned L-type channels will help us better understand the molecular nature of its high [H+] and [Cl−] sensitivity. We proposed to clone L-type Ca 2+ channel functional important subunits (α₁ and β) from salamander retina.; In the present project, we report the cloning and characterization of tiger salamander retinal Ca2+ channel α₁ and β subunits. The cloned retinal Ca2+ channel al subunit contained the molecular signatures of L-type channels and was highly homologous to α _1D subtype. This finding was consistent with conclusions from previous electrophysiological and pharmacological examinations. RT-PCR screening results indicated this clone had some divergent cDNA regions that were retina-specific. The cloned retinal Ca2+ channel β subunit appeared to be a β_2C subtype. The corresponding mRNA for this β subunit was detected exclusively in salamander retina by RT-PCR. The current study places a solid foundation for further examinations on the high [H+ ] and [Cl−] sensitivity of salamander retinal Ca2+ channels.