title: Alternative splice isoforms of small conductance calcium-activated SK2 channels differ in molecular interactions and surface levels.
abstract: Small conductance Ca(2+)-sensitive potassium (SK2) channels are voltage-independent, Ca(2+)-activated ion channels that conduct potassium cations and thereby modulate the intrinsic excitability and synaptic transmission of neurons and sensory hair cells. In the cochlea, SK2 channels are functionally coupled to the highly Ca(2+) permeant α9/10-nicotinic acetylcholine receptors (nAChRs) at olivocochlear postsynaptic sites. SK2 activation leads to outer hair cell hyperpolarization and frequency-selective suppression of afferent sound transmission. These inhibitory responses are essential for normal regulation of sound sensitivity, frequency selectivity, and suppression of background noise. However, little is known about the molecular interactions of these key functional channels. Here we show that SK2 channels co-precipitate with α9/10-nAChRs and with the actin-binding protein α-actinin-1. SK2 alternative splicing, resulting in a 3 amino acid insertion in the intracellular 3' terminus, modulates these interactions. Further, relative abundance of the SK2 splice variants changes during developmental stages of synapse maturation in both the avian cochlea and the mammalian forebrain. Using heterologous cell expression to separately study the 2 distinct isoforms, we show that the variants differ in protein interactions and surface expression levels, and that Ca(2+) and Ca(2+)-bound calmodulin differentially regulate their protein interactions. Our findings suggest that the SK2 isoforms may be distinctly modulated by activity-induced Ca(2+) influx. Alternative splicing of SK2 may serve as a novel mechanism to differentially regulate the maturation and function of olivocochlear and neuronal synapses.
authors.affiliation: Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA.
authors.forename: Elizabeth Storer
authors.initials: ES
authors.lastname: Scholl
authors.affiliation: Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA.
authors.forename: Antonella
authors.initials: A
authors.lastname: Pirone
authors.affiliation: Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Cox
authors.affiliation: Department of Otolaryngology; University of Michigan; Ann Arbor, MI USA.
authors.forename: R Keith
authors.initials: RK
authors.lastname: Duncan
authors.affiliation: Department of Neuroscience; Tufts University Sackler School of Graduate Biomedical Sciences; Boston, MA USA.
authors.forename: Michele H
authors.initials: MH
authors.lastname: Jacob
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D019921:Biotinylation; D001921:Brain / Q000502:physiology; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000502:physiology; D002645:Chickens; D003051:Cochlea / Q000502:physiology; D004705:Endocytosis; D006198:Hair Cells, Auditory / Q000502:physiology; D051379:Mice; D009474:Neurons / Q000502:physiology; D009865:Oocytes; D020033:Protein Isoforms / Q000502:physiology; D011978:Receptors, Nicotinic / Q000502:physiology*; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D002147:Calmodulin; D020033:Protein Isoforms; D011978:Receptors, Nicotinic; D051640:Small-Conductance Calcium-Activated Potassium Channels; D002118:Calcium
keywords: SK channel; calcium; calmodulin; nAChR; neuron; olivocochlear; sensory hair cell; synapse