Calcium activated K+ channels in the electroreceptor of the skate confirmed by cloning. Details of subunits and splicing

• Published in: Gene Vol. 578; no. 1; pp. 63 - 73
• Main Authors: King, Benjamin L., Shi, Ling Fang, Kao, Peter, Clusin, William T.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2016
• Subjects: Alternative Splicing; Amino Acid Sequence; Animals; Brackish; Calcium-activated potassium channel; Cloning, Molecular - methods; Elasmobranchii; Electroreception; Fish Proteins - genetics; Fish Proteins - metabolism; Genome; Hair Cells, Ampulla - enzymology; Humans; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits - genetics; Large-Conductance Calcium-Activated Potassium Channel alpha Subunits - metabolism; Large-Conductance Calcium-Activated Potassium Channels - genetics; Large-Conductance Calcium-Activated Potassium Channels - metabolism; Leucoraja erinacea; Little skate; Marine; Phylogeny; Protein Isoforms - genetics; Protein Isoforms - metabolism; Protein Sorting Signals; Skates (Fish) - genetics; Skates (Fish) - metabolism; Australia; aa; Alternative splicing; Kcnma1; Leucoraja erinacea; BK; mRNA; Kcnmb4; Electroreception; Calcium-activated potassium channel; RT-PCR; Slo; SK; cDNA; Little skate; KCNN3; Genome; cSlo; hSlo; PCR
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/j.gene.2015.12.010

Elasmobranchs detect small potentials using excitable cells of the ampulla of Lorenzini which have calcium-activated K+ channels, first described in 1974. A distinctive feature of the outward current in voltage clamped ampullae is its apparent insensitivity to voltage. The sequence of a BK channel α isoform expressed in the ampulla of the skate was characterized. A signal peptide is present at the beginning of the gene. When compared to human isoform 1 (the canonical sequence), the largest difference was absence of a 59 amino acid region from the S8–S9 intra-cellular linker that contains the strex regulatory domain. The ampulla isoform was also compared with the isoform predicted in late skate embryos where strex was also absent. The BK voltage sensors were conserved in both skate isoforms. Differences between the skate and human BK channel included alternative splicing. Alternative splicing occurs at seven previously defined sites that are characteristic for BK channels in general and hair cells in particular. Skate BK sequences were highly similar to the Australian ghost shark and several other vertebrate species. Based on alignment of known BK sequences with the skate genome and transcriptome, there are at least two isoforms of Kcnma1α expressed in the skate. One of the β subunits (β4), which is known to decrease voltage sensitivity, was also identified in the skate genome and transcriptome and in the ampulla. These studies advance our knowledge of BK channels and suggest further studies in the ampulla and other excitable tissues. •We characterized the BK channel in the skate electroreceptor (ampulla of Lorenzini).•We cloned and characterized cDNAs for the α and β4 subunit.•The presence of BK channels in the ampulla is consistent with the known physiology.•β4 subunits may explain absence of voltage gating of the BK current.•Our results retrospectively confirm the discovery of a new class of K+ channels.