No abstract

The N-type Ca channel alpha1B subunit is localized to synapses throughout the nervous system and couples excitation to release of neurotransmitters. In a previous study, two functionally distinct variants of the alpha1B subunit were identified, rnalpha1B-b and rnalpha1B-d, that differ at two loci;four amino acids [SerPheMetGly (SFMG)] in IIIS3-S4 and two amino acids [GluThr (ET)] in IVS3-S4. These variants are reciprocally expressed in rat brain and sympathetic ganglia (). We now show that the slower activation kinetics of rnalpha1B-b (DeltaSFMG/+ET) compared with rnalpha1B-d (+SFMG/DeltaET) channels are fully accounted for by the insertion of ET in IVS3-S4 and not by the lack of SFMG in IIIS3-S4. We also show that the inactivation kinetics of these two variants are indistinguishable. Through genomic analysis we identify a six-base cassette exon that encodes the ET site and with ribonuclease protection assays demonstrate that the expression of this mini-exon is essentially restricted to alpha1B RNAs of peripheral neurons. We also show evidence for regulated alternative splicing of a six-base exon encoding NP in the IVS3-S4 linker of the closely related alpha1A gene and establish that residues NP can functionally substitute for ET in domain IVS3-S4 of alpha1B. The selective expression of functionally distinct Ca channel splice variants of alpha1B and alpha1A subunits in different regions of the nervous system adds a new dimension of diversity to voltage-dependent Ca signaling in neurons that may be important for optimizing action potential-dependent transmitter release at different synapses.

Alternative splicing is a critical mechanism used extensively in the mammalian nervous system to increase the level of diversity that can be achieved by a set of genes. This review focuses on recent studies of voltage-gated calcium (Ca) channel Ca(v)alpha1 subunit splice isoforms in neurons. Voltage-gated Ca channels couple changes in neuronal activity to rapid changes in intracellular Ca levels that in turn regulate an astounding range of cellular processes. Only ten genes have been identified that encode Ca(v)alpha1 subunits, an insufficient number to account for the level of functional diversity among voltage-gated Ca channels. The consequences of regulated alternative splicing among the genes that comprise voltage-gated Ca channels permits specialization of channel function, optimizing Ca signaling in different regions of the brain and in different cellular compartments. Although the full extent of alternative splicing is not yet known for any of the major subtypes of voltage-gated Ca channels, it is already clear that it adds a rich layer of structural and functional diversity".