Alternative splicing of a short cassette exon in alpha1B generates functionally distinct N-type calcium channels in central and peripheral neurons.
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.
Lin
Z
Z
Department of Neuroscience, Brown University, Providence, Rhode Island 02912, USA.
Lin
Y
Y
Schorge
S
S
Pan
J Q
JQ
Beierlein
M
M
Lipscombe
D
D
D000200:Action Potentials / Q000502:physiology; D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D020013:Calcium Signaling; D002490:Central Nervous System / Q000166:cytology / Q000378:metabolism*; D005091:Exons / Q000235:genetics*; D015870:Gene Expression; D015640:Ion Channel Gating; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D017933:Peripheral Nervous System / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017384:Sequence Deletion; D014982:Xenopus laevis
D015220:Calcium Channels; D020033:Protein Isoforms; D012333:RNA, Messenger