Korean J Physiol Pharmacol.  2008 Feb;12(1):25-30. 10.4196/kjpp.2008.12.1.25.

Involvement of Thromboxane A2 in the Modulation of Pacemaker Activity of Interstitial Cells of Cajal of Mouse Intestine

• Kim JH
• Choi SJ
• Yeum CH
• Yoon PJ
• Choi S
• Jun JY

• KMID: 2071642
• DOI: http://doi.org/10.4196/kjpp.2008.12.1.25

Abstract

Although many studies show that thromboxane A2 (TXA2) has the action of gastrointestinal (GI) motility using GI muscle cells and tissue, there are no reports on the effects of TXA2 on interstitial cells of Cajal (ICC) that function as pacemaker cells in GI tract. So, we studied the modulation of pacemaker activities by TXA2 in ICC with whole cell patch-clamp technique. Externally applied TXA2 (5 micrometer) produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The tonic inward currents by TXA2 were inhibited by intracellular application of GDP-beta-S. The pretreatment of ICC with Ca2+ free solution and thapsigargin, a Ca2+-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the TXA2-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the TXA2-induced effects on pacemaker currents. These results suggest that TXA2 can regulate intestinal motility through the modulation of ICC pacemaker activities. This modulation of pacemaker activities by TXA2 may occur by the activation of G protein and PKC independent pathway via extra and intracellular Ca2+ modulation.

Keyword

Thromboxane A2 (TXA2); Interstitial cells of Cajal (ICC); Pacemaker currents; Intestinal motility

MeSH Terms

Animals
Benzophenanthridines
Endoplasmic Reticulum
Gastrointestinal Motility
Gastrointestinal Tract
GTP-Binding Proteins
Guanosine Diphosphate
Interstitial Cells of Cajal
Intestines
Membranes
Mice
Muscle Cells
Naphthalenes
Patch-Clamp Techniques
Protein Kinase C
Thapsigargin
Thionucleotides
Thromboxane A2
Benzophenanthridines
GTP-Binding Proteins
Guanosine Diphosphate
Naphthalenes
Protein Kinase C
Thapsigargin
Thionucleotides
Thromboxane A2

Figure

• 

  Fig. 1. The effects of TXA2 on pacemaker potentials and pacemaker currents recorded in cultured ICC from mouse small intestine (A) Pacemaker potentials of ICC which were exposed to TXA2 (5 μM) in the current-clamping mode (I=0). Vertical solid line scales amplitude of pacemaker potential and horizontal solid line scales for duration of recording (s) pacemaker potentials. (B), (C), and (D) Pacemaker currents of ICC recorded at a holding potential of −70 mV, when exposed to various concentrations of TXA2 (1, 3, and 5 μM). The dotted lines indicate zero current levels. Vertical solid line scales amplitude of pacemaker current and horizontal solid line scales duration of recording (s) pacemaker currents. The responses to TXA2 are summarized in (E), (F) and (G). The bars represent mean values±SE. ∗∗Significantly different from the untreated control (Con) (p < 0.01).

• 

  Fig. 2. The effects of GDP-β-S in response to TXA2 induced pacemaker currents from ICC of mouse small intestine (A) Pacemaker currents from ICC exposed to TXA2 (5 μM) in the presence of GDP-β-S (1 mM) in the pipette. The tonic inward currents with suppressed amplitudes and frequency induced by TXA2 were blocked by internally applied GDP-β-S (1 mM). The dotted lines indicate the zero current levels. The effects of TXA2 in the presence of GDP-β-S are summarized in (B). Vertical solid line scales amplitude of pacemaker current and horizontal solid line scales for duration of recording (s) pacemaker currents. Bars represent mean values ± SE. The effects of GDP-β-S on TXA2-induced pacemaker currents were significantly different from the TXA2-induced pacemaker currents (p < 0.01). The bars represent mean values±SE. ∗∗Significantly different from the untreated control (Con) (p < 0.01).

• 

  Fig. 3. The effects of an external Ca2+-free solution or thapsigargin on the TXA2-induced response on pacemaker currents in cultured ICC from mouse small intestine (A) External Ca2+-free solution abolished the generation of pacemaker currents. Under this condition, the TXA2 (5μM)-induced tonic inward currents were blocked. (C) Thapsigargin (5μM) abolished the generation of pacemaker currents. Thapsigargin also blocked the TXA2 (5μM)-induced tonic inward currents. The dotted lines indicate the zero current levels. Responses to the TXA2 in the external Ca2+-free solution and in the presence of thapsigargin are summarized in (B) and (D). Vertical solid line scales amplitude of pacemaker current and horizontal solid line scales duration of recording (s) pacemaker current. The bars represent mean values ± SE. ∗∗Significantly different from the untreated Control (Con) (p < 0.01).

• 

  Fig. 4. The effects of chelerythrine or calphostin C on the TXA2-induced response on pacemaker currents in cultured ICC from mouse small intestine (A), (B) Pacemaker currents of ICC exposed to TXA2 (10 μM) in the presence of chelerythrine (1μM) or calphostin C (0.1μM). In this condition, the TXA2 caused tonic inward currents. The dotted lines indicate the zero current levels. Responses to the TXA2 in the presence of chelerythrine or calphostin C are summarized in (C). Vertical solid line scales amplitude of pacemaker current and horizontal solid line scales duration of recording (s) pacemaker current. The bars represent mean values ± SE.

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