title: Maxi-K channels localize to caveolae in human myometrium: a role for an actin-channel-caveolin complex in the regulation of myometrial smooth muscle K+ current.
abstract: Multiple cell-signaling pathways converge to modulate large-conductance, voltage- and Ca2+-sensitive K+ channel (maxi-K channel) activity and buffer cell excitability in human myometrial smooth muscle cells (hMSMCs). Recent evidence indicates that maxi-K channel proteins can target to membrane microdomains; however, their association with other proteins within these macromolecular complexes has not been elucidated. Biochemical isolation of detergent-resistant membrane fractions from human myometrium demonstrates the presence of maxi-K channels in lipid raft microdomains, which cofractionate with caveolins. In both nonpregnant and late-pregnant myometrium, maxi-K channels associate and colocalize with caveolar scaffolding proteins caveolin-1 and caveolin-2, but not caveolin-3. Disruption of cultured hMSMC caveolar complexes by cholesterol depletion with cyclodextrin increases an iberiotoxin-sensitive K+ current. Co-immunoprecipitations have indicated that the maxi-K channel also is associated with both alpha- and gamma-actin. Immunocytochemical analysis indicates colocalization of maxi-K channels, actin, and caveolin-1 in primary cultures of hMSMCs. Further experiments using immunoelectron microscopy have shown the proximity of both actin and the maxi-K channel within the same cell surface caveolar structures. Functionally, disruption of the actin cytoskeleton in cultured hMSMCs by cytochalasin D and latrunculin A greatly increased the open-state probability of the channel, while stabilization of actin cytoskeleton with jasplakinolide abolished the effect of latrunculin A. These data indicate that the actin cytoskeleton is involved as part of a caveolar complex in the regulation of myometrial maxi-K channel function.
authors.affiliation: Department of Physiology and Biophysics, Carver College of Medicine, University of Iowa, 5-660 Bowen Science Bldg., Iowa City, Iowa 52242, USA.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Brainard
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Miller
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Martens
authors.forename: Sarah K
authors.initials: SK
authors.lastname: England
mesh_terms: D000199:Actins / Q000378:metabolism*; D021941:Caveolae / Q000378:metabolism*; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism*; D003599:Cytoskeleton / Q000502:physiology; D004553:Electric Conductivity; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009130:Muscle, Smooth / Q000378:metabolism; D009215:Myometrium / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism* / Q000502:physiology; D011247:Pregnancy; D014018:Tissue Distribution
chemical_list: D000199:Actins; C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D007473:Ion Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated