Rat brain expresses a heterogeneous family of calcium channels.
We describe the isolation and characterization of several rat brain cDNAs that are homologous to the alpha 1 subunit of heart and skeletal muscle dihydropyridine-sensitive Ca channels. Northern blot analysis of 32 cDNAs shows that they can be grouped into four distinct classes (A, B, C, and D), each corresponding to a distinct hybridization pattern of brain mRNAs. Southern blot and DNA sequencing suggest that each class of cDNA represents a distinct gene or gene family. In the regions sequenced, the rat brain class C and D gene products share approximately 75% amino acid identity with the rabbit skeletal muscle Ca channel. In addition, the class C polypeptide is almost identical to the rabbit cardiac Ca channel (97% identity). In contrast, the rat brain class A and B cDNAs are more distantly related to dihydropyridine-sensitive Ca channels (47-64% amino acid identity) and to the brain class C and D genes (51-55% amino acid identity). To examine the functional significance of the isolated brain cDNAs, hybrid depletion experiments were performed in Xenopus oocytes. Antisense oligonucleotides against class A and B cDNAs each partially inhibited, and a class C oligonucleotide almost fully inhibited, the expression of Ba current in rat brain mRNA injected oocytes; but none of the oligonucleotides affected the expression of voltage-gated Na or K conductances. The clone characterization and sequencing results demonstrate that a number of distinct, yet related, voltage-gated Ca-channel genes are expressed in the brain. The antisense oligonucleotide experiments specifically show that one or several of the Ca-channel classes are related to the Ca channels observed in rat brain mRNA injected oocytes.
Snutch
T P
TP
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
Leonard
J P
JP
Gilbert
M M
MM
Lester
H A
HA
Davidson
N
N
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009693:Nucleic Acid Hybridization; D015345:Oligonucleotide Probes; D012313:RNA / Q000235:genetics / Q000302:isolation & purification; D051381:Rats; D012689:Sequence Homology, Nucleic Acid
D015220:Calcium Channels; D008565:Membrane Proteins; D015345:Oligonucleotide Probes; D012313:RNA; D004247:DNA