title: BK channel β1 subunits regulate airway contraction secondary to M2 muscarinic acetylcholine receptor mediated depolarization.
abstract: The large conductance calcium- and voltage-activated potassium channel (BK channel) and its smooth muscle-specific β1 subunit regulate excitation–contraction coupling in many types of smooth muscle cells. However, the relative contribution of BK channels to control of M2- or M3-muscarinic acetylcholine receptor mediated airway smooth muscle contraction is poorly understood. Previously, we showed that knockout of the BK channel β1 subunit enhances cholinergic-evoked trachea contractions. Here, we demonstrate that the enhanced contraction of the BK β1 knockout can be ascribed to a defect in BK channel opposition of M2 receptor-mediated contractions. Indeed, the enhanced contraction of β1 knockout is eliminated by specific M2 receptor antagonism. The role of BK β1 to oppose M2 signalling is evidenced by a greater than fourfold increase in the contribution of L-type voltage-dependent calcium channels to contraction that otherwise does not occur with M2 antagonist or with β1 containing BK channels. The mechanism through which BK channels oppose M2-mediated recruitment of calcium channels is through a negative shift in resting voltage that offsets, rather than directly opposes, M2-mediated depolarization. The negative shift in resting voltage is reduced to similar extents by BK β1 knockout or by paxilline block of BK channels. Normalization of β1 knockout baseline voltage with low external potassium eliminated the enhanced M2-receptor mediated contraction. In summary, these findings indicate that an important function of BK/β1 channels is to oppose cholinergic M2 receptor-mediated depolarization and activation of calcium channels by restricting excitation–contraction coupling to more negative voltage ranges.
authors.affiliation: Department of Physiology, UT Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
authors.forename: Iurii
authors.initials: I
authors.lastname: Semenov
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.forename: Jeremiah T
authors.initials: JT
authors.lastname: Herlihy
authors.forename: Robert
authors.initials: R
authors.lastname: Brenner
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology; D056966:Excitation Contraction Coupling / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000037:antagonists & inhibitors / Q000502:physiology*; D015656:Respiratory Mechanics; D015398:Signal Transduction; D014132:Trachea / Q000187:drug effects / Q000502:physiology*
chemical_list: D020746:Calcium Channels, L-Type; D007211:Indoles; C543091:Kcnmb1 protein, mouse; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D018727:Muscarinic Antagonists; D026902:Potassium Channel Blockers; D043585:Receptor, Muscarinic M2; D010890:Pirenzepine; C048220:paxilline; C048593:otenzepad