title: Ca2+- and thromboxane-dependent distribution of MaxiK channels in cultured astrocytes: from microtubules to the plasma membrane.
abstract: Large-conductance, voltage- and Ca2+-activated K+ channels (MaxiK) are broadly expressed ion channels minimally assembled by four pore-forming alpha-subunits (MaxiKalpha) and typically observed as plasma membrane proteins in various cell types. In murine astrocyte primary cultures, we show that MaxiKalpha is predominantly confined to the microtubule network. Distinct microtubule distribution of MaxiKalpha was visualized by three independent labeling approaches: (1) MaxiKalpha-specific antibodies, (2) expressed EGFP-labeled MaxiKalpha, and (3) fluorophore-conjugated iberiotoxin, a specific MaxiK pore-blocker. This MaxiKalpha association with microtubules was further confirmed by in vitro His-tag pulldown, co-immunoprecipitation from brain lysates, and microtubule depolymerization experiments. Changes in intracellular Ca2+ elicited by general pharmacological agents, caffeine or thapsigargin, resulted in increased MaxiKalpha labeling at the plasma membrane. More notably, U46619, an analog of thromboxane A2 (TXA2), which triggers Ca2+-release pathways and whose levels increase during cerebral hemorrhage/trauma, also elicits a similar increase in MaxiKalpha surface labeling. Whole-cell patch clamp recordings of U46619-stimulated cells develop a approximately 3-fold increase in current amplitude indicating that TXA2 stimulation results in the recruitment of additional, functional MaxiK channels to the surface membrane. While microtubules are largely absent in mature astrocytes, immunohistochemistry results in brain slices show that cortical astrocytes in the newborn mouse (P1) exhibit a robust expression of microtubules that significantly colocalize with MaxiK. The results of this study provide the novel insight that suggests that Ca2+ released from intracellular stores may play a key role in regulating the traffic of intracellular, microtubule-associated MaxiK stores to the plasma membrane of developing murine astrocytes.
authors.affiliation: Department of Molecular and Medical Pharmacology, University of California at Los Angeles, Los Angeles, California, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Ou
authors.forename: Y
authors.initials: Y
authors.lastname: Kumar
authors.forename: A
authors.initials: A
authors.lastname: Alioua
authors.forename: C
authors.initials: C
authors.lastname: Sailer
authors.forename: E
authors.initials: E
authors.lastname: Stefani
authors.forename: L
authors.initials: L
authors.lastname: Toro
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism*; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002491:Central Nervous System Agents / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008870:Microtubules / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives; D014404:Tubulin / Q000378:metabolism
chemical_list: D002491:Central Nervous System Agents; D002614:Chelating Agents; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D014404:Tubulin; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D002110:Caffeine; D004533:Egtazic Acid; D013928:Thromboxane A2; D019284:Thapsigargin; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D002118:Calcium