title: The β1-subunit of the MaxiK channel associates with the thromboxane A2 receptor and reduces thromboxane A2 functional effects.
abstract: The large conductance voltage- and Ca(2+)-activated K(+) channel (MaxiK, BK(Ca), BK) is composed of four pore-forming α-subunits and can be associated with regulatory β-subunits. One of the functional roles of MaxiK is to regulate vascular tone. We recently found that the MaxiK channel from coronary smooth muscle is trans-inhibited by activation of the vasoconstricting thromboxane A(2) prostanoid receptor (TP), a mechanism supported by MaxiK α-subunit (MaxiKα)-TP physical interaction. Here, we examined the role of the MaxiK β1-subunit in TP-MaxiK association. We found that the β1-subunit can by itself interact with TP and that this association can occur independently of MaxiKα. Subcellular localization analysis revealed that β1 and TP are closely associated at the cell periphery. The molecular mechanism of β1-TP interaction involves predominantly the β1 extracellular loop. As reported previously, TP activation by the thromboxane A(2) analog U46619 caused inhibition of MaxiKα macroscopic conductance or fractional open probability (FP(o)) as a function of voltage. However, the positive shift of the FP(o) versus voltage curve by U46619 relative to the control was less prominent when β1 was coexpressed with TP and MaxiKα proteins (20 ± 6 mV, n = 7) than in cells expressing TP and MaxiKα alone (51 ± 7 mV, n = 7). Finally, β1 gene ablation reduced the EC(50) of the U46619 agonist in mediating aortic contraction from 18 ± 1 nm (n = 12) to 9 ± 1 nm (n = 12). The results indicate that the β1-subunit can form a tripartite complex with TP and MaxiKα, has the ability to associate with each protein independently, and diminishes U46619-induced MaxiK channel trans-inhibition as well as vasoconstriction.
authors.affiliation: Department of Anesthesiology, UCLA, Los Angeles, California 90095-7115, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Zhu
authors.initials: Z
authors.lastname: Zhang
authors.forename: Huilin
authors.initials: H
authors.lastname: Koh
authors.forename: Rong
authors.initials: R
authors.lastname: Lu
authors.forename: Zhaorong
authors.initials: Z
authors.lastname: Jiang
authors.forename: Abderrahmane
authors.initials: A
authors.lastname: Alioua
authors.forename: Jesus
authors.initials: J
authors.lastname: Garcia-Valdes
authors.forename: Enrico
authors.initials: E
authors.lastname: Stefani
authors.forename: Ligia
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; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000378:metabolism; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding / Q000187:drug effects; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000378:metabolism*; D013928:Thromboxane A2 / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid