Generation and Role of Oscillatory Contractions in Mouse Airway Smooth Muscle

Abstract

Background/Aims: Tetraethylammonium chloride (TEA) induces oscillatory contractions in mouse airway smooth muscle (ASM); however, the generation and maintenance of oscillatory contractions and their role in ASM are unclear. Methods: In this study, oscillations of ASM contraction and intracellular Ca²⁺ were measured using force measuring and Ca²⁺ imaging technique, respectively. TEA, nifedipine, niflumic acid, acetylcholine chloride, lithium chloride, KB-R7943, ouabain, 2-Aminoethoxydiphenyl borate, thapsigargin, tetrodotoxin, and ryanodine were used to assess the mechanism of oscillatory contractions. Results: TEA induced depolarization, resulting in activation of L-type voltage-dependent Ca²⁺ channels (LVDCCs) and voltage-dependent Na⁺ (V_Na) channels. The former mediated Ca²⁺ influx to trigger a contraction and the latter mediated Na⁺ entry to enhance the contraction via activating LVDCCs. Meanwhile, increased Ca²⁺-activated Cl^- channels, inducing depolarization that resulted in contraction through LVDCCs. In addition, the contraction was enhanced by intracellular Ca²⁺ release from Ca²⁺ stores mediated by inositol (1,4,5)-trisphosphate receptors (IP₃Rs). These pathways together produce the contractile phase of the oscillatory contractions. Furthermore, the increased Ca²⁺ activated the Na⁺-Ca²⁺ exchanger (NCX), which transferred Ca²⁺ out of and Na⁺ into the cells. The former induced relaxation and the latter activated Na⁺/K⁺-ATPase that induced hypopolarization to inactivate LVDCCs causing further relaxation. This can also explain the relaxant phase of the oscillatory contractions. Moreover, the depolarization induced by V_Na channels and NCX might be greater than the hypopolarization caused by Na⁺/K⁺-ATPase alone, inducing LVDCC activation and resulting in further contraction. Conclusions: These data indicate that the TEA-induced oscillatory contractions were cooperatively produced by LVDCCs, V_Na channels, Ca²⁺-activated Cl^- channels, NCX, Na⁺/K⁺ ATPase, IP₃Rs-mediated Ca²⁺ release, and extracellular Ca²⁺.

The Other Side of the Fascia: The Smooth Muscle Part 1

“…The activation of L-type voltage-dependent calcium channels (LVDCCs) allows Ca2+ to enter the cytosol; this increase in calcium will activate the opening of Clca channels, which will mediate chloride efflux and membrane depolarization, also activating LVDCCs for an optimal contraction. The calcium concentration in the cytosol is managed by Na+-Ca2+ exchanger (NCX), that places one calcium molecule in the extracellular space and three sodium molecules in the cytoplasm, inducing a decreased amount of calcium and muscles relaxation [24]. Rhythmic contraction is supported by the deformation of the contractile smooth cell [24].…”

“…The calcium concentration in the cytosol is managed by Na+-Ca2+ exchanger (NCX), that places one calcium molecule in the extracellular space and three sodium molecules in the cytoplasm, inducing a decreased amount of calcium and muscles relaxation [24]. Rhythmic contraction is supported by the deformation of the contractile smooth cell [24]. Cytoplasmic calcium activates Ca2+/calmodulin-dependent Myosin light-chain kinase (MYLC or MLCK) that phosphorylates a specific myosin light chain (RLC) associated with the actin to produce contractile strength.…”

Transition From Phasic to Tonic Contractility in Airway Smooth Muscle After Birth: An Experimental and Computational Modeling Study

“…For example, charybdotoxin-induced oscillatory contraction in guinea pig airways is regulated by activation of the cyclooxygenase two enzyme and downstream production of prostaglandins [34]. In murine airways, tetraethylammonium chloride induced oscillations in intracellular Ca 2+ and force were produced cooperatively by L-type voltage-dependent Ca 2+ channels, voltage-dependent Na + channels, Ca 2+ -activated Cl − channels, Na + –Ca 2+ exchanger, Na + /K + ATPase, release from Ca 2+ stores mediated by inositol (1,4,5)-trisphosphate, and extracellular Ca 2+ [35]. Whether phasic ASM contraction occurs appears dependent on the frequency of Ca 2+ oscillation, wherein frequencies exceeding 40 cycles/min produce sustained (tonic) contraction [30] and phasic ASM contraction at much lower frequencies [31].…”

Estrogenic Modulation of Ionic Channels, Pumps and Exchangers in Airway Smooth Muscle

“…Both types of Ca 2+ changes participate in triggering ASM contraction, and they might participate in other physiological processes in the ASM. Remarkably, these oscillations augment [Ca 2+ ]i, an increase that activates NCX, initiating the relaxation phase by extruding Ca 2+ [92]. Alterations of the NCX also participate in pathological conditions; TNF-α or IL-13 treatment of hASM cells upregulated the expression of NCX1, and the treatment with KB-R7943 abolished methacholine induced AHR in an allergic mouse model [91,93].…”

“…During oscillatory contractions in mouse ASM induced by TEA, NKA has been identified to participate in the relaxation phase of the oscillations. When activated, NKA reduces the differential potential of the cellular membrane, inactivating LVDCCs and causing relaxation [92]. It should be mentioned that TEA is a drug used to induce ASM contraction by depolarizing the membrane through the inhibition of K + channels.…”