Korean J Physiol Pharmacol.  2013 Aug;17(4):359-365. 10.4196/kjpp.2013.17.4.359.

Mechanism of Relaxation Via TASK-2 Channels in Uterine Circular Muscle of Mouse

• Hong SH
• Sung R
• Kim YC
• Suzuki H
• Choi W
• Park YJ
• Ji IW
• Kim CH
• Myung SC
• Lee MY
• Kang TM
• You RY
• Lee KJ
• Lim SW
• Yun HY
• Song YJ
• Xu WX
• Kim HS
• Lee SJ

• KMID: 2285471
• DOI: http://doi.org/10.4196/kjpp.2013.17.4.359

Abstract

Plasma pH can be altered during pregnancy and at labor. Membrane excitability of smooth muscle including uterine muscle is suppressed by the activation of K+ channels. Because contractility of uterine muscle is regulated by extracellular pH and humoral factors, K+ conductance could be connected to factors regulating uterine contractility during pregnancy. Here, we showed that TASK-2 inhibitors such as quinidine, lidocaine, and extracellular acidosis produced contraction in uterine circular muscle of mouse. Furthermore, contractility was significantly increased in pregnant uterine circular muscle than that of non-pregnant muscle. These patterns were not changed even in the presence of tetraetylammonium (TEA) and 4-aminopyridine (4-AP). Finally, TASK-2 inhibitors induced strong myometrial contraction even in the presence of L-methionine, a known inhibitor of stretchactivated channels in myometrium. When compared to non-pregnant myometrium, pregnant myometrium showed increased immunohistochemical expression of TASK-2. Therefore, TASK-2, seems to play a key role during regulation of myometrial contractility in the pregnancy and provides new insight into preventing preterm delivery.

Keyword

Relaxation; TASK-2; Uterus

MeSH Terms

4-Aminopyridine
Acidosis
Animals
Contracts
Female
Hydrogen-Ion Concentration
Lidocaine
Membranes
Methionine
Mice
Muscle, Smooth
Muscles
Myometrium
Plasma
Pregnancy
Quinidine
Relaxation
Uterine Contraction
Uterus
4-Aminopyridine
Lidocaine
Methionine
Quinidine

Figure

• 

  Fig. 1 Spontaneous and oxitocin (OXT)-induced contraction in uterine circular muscle of mouse. (A) Uterine circular muscle shows spontaneous phasic contraction in both non-pregnant (0.5 g) and pregnant myometrium (0.6 g). (B) OXT produced initial and tonic contractions however tonic component was not persistent in non-pregnant uterine circular muscle. Initial contractions by OXT were 0.4 g (non-pregnant) and 1.1 g (pregnant). However, tonic contraction were 0.3 g (non-pregnant) and 0.8 g (pregnant) (p<0.05). Data was summarized in right panel. Asterisks show a statistical significance (p<0.05).

• 

  Fig. 2 Effect of quinidine on spontaneous electrical activity of murine myometrium. (A) Electrical responses were recorded from circular smooth muscle cells of the mouse uterus. In intact tissues, circular muscle cells were spontaneously active with generation of plateau-type action potentials. (B) The spontaneous action potentials were inhibited by nifedipine. (C) Application of quinidine and high K+ depolarized the membrane, in a concentration-dependent manner, with generation of spike potentials.

• 

  Fig. 3 Effect of quinidine and extracellular acidosis on isometric contraction of uterine circular muscle of mouse. (A) Quinidine (50 µM) produced phasic contraction of non-pregnant myometrium. Quinidine-induced tonic contraction of pregnant myometrium was increased compared to that of non-pregnant myometrium. (B) Extracellular acidosis (pHo=6.4) produced contraction in non-pregnant myometrium. This contraction was also increased compared to that of non-pregnant myometrium.

• 

  Fig. 4 Effect of TEA and 4-AP on isometric contraction of uterine circular muscle of mouse. (A) TEA (2~5 mM) produced concentration-dependent phasic contraction in non-pregnant uterine circular muscle. However, it did not show any effect in pregnant uterine circular muscle (right panel). (B) In the presence of TEA and 4-AP, effect of stretch-dependent K2P channels (TREK-1) inhibitor (L-methionine) was studied. L-methionine (1 mM) produced contractions that spontaneously decayed to near baseline values within 10~15 min in pregnant uterine circular muscle. However, it did not show significant effect in non-pregnant uterine circular muscle. Data from pregnant uterine circular muscle was summarized in right panel.

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  Fig. 5 Regulation of contraction of uterine circular muscle by TASK-2 channel inhibitors in the presence of TEA, 4-AP and L-methionine. The TASK-2 channel inhibitors produced contractions in uterine circular muscle. (A, B) Adding quinidine or lidocaine in the presence of L-methionine produced further robust contractions of uterine circular muscle. Contraction by TASK-2 channel inhibitors was increased in pregnant uterine circular muscle.

• 

  Fig. 6 Identification of TASK-2 channels by immunohistochemistry in uterine circular muscle. We tried to elucidate expression and increase of TASK-2 channels during pregnancy using immunohistochemistry. (A, B) Immunoreactivity for TASK-2 channel antibody in pregnant uterine circular muscle was more even compared to that of non-pregnant uterine circular muscle.

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