title: Expression of Ca2+-activated BK channel mRNA and its splice variants in the rat cochlea.
abstract: Voltage-activated K(+) channels are important for shaping the receptor potentials of cochlear hair cells. In particular, the functional maturation of inner hair cells in mice around the onset of hearing coincides with the expression of a large, fast K(+) conductance, probably mediated by Ca(2+)-activated K(+) (BK) channels. In hearing organs of lower vertebrates, frequency tuning depends on BK-type K(+) channels with different kinetics. Kinetics are varied by alternative splicing of the channels' alpha subunits and combination with modulating beta subunits. It is unclear whether similar mechanisms "fine tune" mammalian hair cells. We used various polymerase chain reaction (PCR) approaches to screen rat cochleae for splice variants of BK-type alpha subunits. We isolated mainly minimal variants and only occasionally splice variants with additional inserts. We conclude that alpha subunits with different kinetics are not substantially used in the rat cochlea. However, we isolated six variants differing in their extreme C-terminal sequences, which may be involved in the targeting of the channel protein. By using reverse transcriptase-PCR, we demonstrated also the expression of transcripts for several beta subunits. In situ hybridization experiments revealed strict coexpression of alpha with beta1 transcripts. In inner hair cells, strong labeling emerged shortly before the onset of hearing. Labeling of outer hair cells appeared later and generally weaker. Thus, our molecular data confirm electrophysiological results that suggested that BK channels underlie the large K(+) conductance in inner hair cells of mammals. Extensive splicing of BK channel transcripts, however, does not seem to be used in mammalian hair cells as is done in lower vertebrates.
authors.affiliation: Institute of Physiology II, University of Tübingen, D-72076 Tübingen, Germany.
authors.forename: Patricia
authors.initials: P
authors.lastname: Langer
authors.forename: Stefan
authors.initials: S
authors.lastname: Gründer
authors.forename: Alfons
authors.initials: A
authors.lastname: Rüsch
mesh_terms: D000818:Animals; D001483:Base Sequence; D003051:Cochlea / Q000502:physiology*; D014644:Genetic Variation; D006199:Hair Cells, Auditory, Inner / Q000502:physiology; D017403:In Situ Hybridization; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009419:Nerve Tissue Proteins / Q000032:analysis; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000032:analysis; D024681:Potassium Channels, Calcium-Activated / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013136:Spiral Ganglion / Q000502:physiology
chemical_list: C494842:Kcnma1 protein, rat; C485821:Kcnmb4 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; D012333:RNA, Messenger