Imatinib blocks spontaneous mechanical activities in the adult mouse small intestine: possible inhibition of c-Kit signaling

Identification of CD44 as a Cell-Surface Marker for Kit Negative Interstitial Cells of Cajal in Adult Mouse Colon

Loss of Kit protein expression is proven to influence the plasticity of interstitial cells of Cajal (ICCs) and may contribute to gastrointestinal (GI) dysfunctions. The role and fate of Kit negative ICCs are unclear, and cell-specific markers for the Kit ICCs are unknown. In this study, we treated adult mice with imatinib (a Kit signaling blocker) for 8 or 16 days and investigated whether CD44 is a specific marker for the Kit negative ICCs in the adult mouse colon. We aimed at examining the protein and mRNA level of CD44 and Kit by using Western blot and real-time RT-PCR, respectively. Our results indicated that Kit expression was downregulated for both protein and mRNA levels after imatinib treatment for 8 or 16 days as compared to the vehicle-treated mice. Interestingly, CD44 expression remained unchanged throughout the treatment. Immunostaining on whole-mount preparations for Kit and CD44 showed that CD44 was exclusively co-localized with Kit in the ICCs of the vehicle-treated mouse colon. After imatinib treatment, a number of CD44+/Kit- cells with elaborated processes were observed with an evident decrease of Kit+ cell number within the muscular layers (ICC-IM) and around the myenteric nerve plexus (ICC-MY) as compared to vehicle-treated mice. After discontinuing imatinib for 16 days, Kit+ ICC-MY and ICC-IM were completely co-localized with normalization of CD44 and Kit+ cell numbers. Overall, our results identify CD44 as a cell-specific surface marker for Kit-ICCs and may be useful to understand the role and fate of Kit- ICCs in GI disorders.

Developments in research on interstitial Cajal-like cells in the biliary tract

INTRODUCTION

Interstitial cells of Cajal (ICCs) are a special type of interstitial cells located in the gastrointestinal tract muscles. They are closely related to smooth muscle cells and neurons, participate in gastrointestinal motility and nerve signal transmission, and are pacemaker cells for gastrointestinal electrical activity. Research interest in ICCs has continuously grown since they were first discovered in 1893. Later, researchers discovered that they are also present in other organs, including the biliary tract, urethra, bladder, etc.; these cells were named interstitial Cajal-like cells (ICLCs), and attempts have been made to explain their relationships with certain diseases.

AREAS COVERED

This review paper summarizes the morphology, identification, classification, function, and distribution of ICLCs in the biliary tract and their relationship to biliary tract diseases.

EXPERT OPINION

Based on the function and distribution of ICLCs in the biliary tract system, ICLCs will provide a more reliable theoretical basis for the mechanisms of pathogenesis of and treatments for biliary tract diseases.

Involvement of interstitial cells of Cajal in experimental severe acute pancreatitis in rats

AIM: To observe the changes in interstitial cells of Cajal (ICC) in rats with experimental severe acute pancreatitis (SAP).

METHODS: A total of twenty-four SD rats were randomly divided into two groups (n = 12), namely the sham (S) group and the SAP group; the SAP rat model was established by retrograde injection of 5% sodium taurocholate (1.0 mL/kg) into the pancreatic duct. Twenty-four hours later intestinal motility was assessed by testing small intestinal propulsion rate, and then the rats were sacrificed. The pancreas and jejunum were resected and underwent routine pathologic examination. Immunohistochemical staining was used to detect c-kit-positive cells in the jejunum. Expression of c-kit mRNA was detected by real-time polymerase chain reaction, and the expression of c-kit protein was evaluated by Western blotting. Ultrastructure of ICC was evaluated by transmission electron microscopy.

RESULTS: There was bleeding, necrosis and a large amount of inflammatory cell infiltration in pancreatic tissue in the SAP group, while in jejunal tissue we observed a markedly denuded mucosal layer, loss of villous tissue and a slightly dilated muscular layer. The small intestinal propulsion rate was 68.66% ± 2.66% in the S group and 41.55% ± 3.85% in the SAP group. Compared with the S group, the rate of the SAP group decreased sharply. The density of c-kit-positive cells in the SAP group was significantly lower than in the S group; the respective mean densities were 88.47 ± 10.49 in the S group and 56.11 ± 7.09 in the SAP group. The levels of c-kit protein and mRNA were 0.36 ± 0.04 and 1.29 ± 0.91 in the SAP group, respectively, which were significantly lower than those in the S group (0.53 ± 0.06, 0.64 ± 0.33, respectively). In the SAP group, ICC profiles showed the same change tendency, such as vacuolation of mitochondria, irregular vacuoles and loosened desmosome-like junctions.

CONCLUSION: Decreased c-kit-positive cells and ultrastructural changes in ICC resulting from blockade of the c-kit signaling pathway are involved in the intestinal dysmotility associated with SAP.

Late embryonic and postnatal development of interstitial cells of cajal in mouse esophagus: distribution, proliferation and kit dependence

This paper investigates alterations in interstitial cells of Cajal (ICC) in the esophagus of mice from embryonic day 13.5 (E13.5) to 36 days postpartum (P0-P36) using immunohistochemistry. At E13.5, Kit+ cells presented in clusters and differentiated into spindle-like cells with biopolar processes within the outer (longitudinal) and inner (circular) muscle layers at E17.5. These Kit+ ICC with long processes were also Ano1+ and prominent at birth. The density of ICC gradually decreased, and at P36 it became about one twentieth of that at birth. Kit ligand (stem cell factor) expression is lower in striated muscle cells than that in smooth muscle cells. The ICC number was higher in the distal (close to the cardia) than in the proximal esophagus (close to the pharynx). Some Kit+/Ki67+ and Kit+/bromodeoxyuridine+ cells were observed within the muscle layers, and proliferation persisted from birth through adulthood (P28) with a gradually decreasing cell number. At 24 h, Kit+ ICC were dramatically decreased and almost missing 48 h after administration of imatinib (a Kit inhibitor). Our results indicate that ICC proliferation is age dependent and persists throughout the postnatal period. There is a dramatic decrease in the ICC number from P0 to adult life. The Kit signal is essential for the postnatal development of ICC in the esophagus.

Receptor tyrosine and MAP kinase are involved in effects of H(2)O(2) on interstitial cells of Cajal in murine intestine

Hydrogen peroxide (H(2)O(2)) is involved in intestinal motility through changes of smooth muscle activity. However, there is no report as to the modulatory effects of H(2)O(2) on interstitial cells of Cajal (ICC). We investigated the H(2)O(2) effects and signal transductions to determine whether the intestinal motility can be modulated through ICC. We performed whole-cell patch clamp in cultured ICC from murine intestine and molecular analyses. H(2)O(2) hyperpolarized the membrane and inhibited pacemaker currents. These effects were inhibited by glibenclamide, an inhibitor of ATP-sensitive K+ (K(ATP)) channels. The free-radical scavenger catalase inhibited the H(2)O(2)-induced effects. MAFP and AACOCF3 (a cytosolic phospholipase A2 inhibitors) or SC-560 and NS-398 (a selective COX-1 and 2 inhibitor) or AH6809 (an EP2 receptor antagonist) inhibited the H(2)O(2)-induced effects. PD98059 (a mitogen activated/ERK-activating protein kinase inhibitor) inhibited the H(2)O(2)-induced effects, though SB-203580 (a p38 MAPK inhibitor) or a JNK inhibitor did not affect. H(2)O(2)-induced effects could not be inhibited by LY-294002 (an inhibitor of PI3-kinases), calphostin C (a protein kinase C inhibitor) or SQ-22536 (an adenylate cyclase inhibitor). Adenoviral infection analysis revealed H2O2 stimulated tyrosine kinase activity and AG 1478 (an antagonist of epidermal growth factor receptor tyrosine kinase) inhibited the H(2)O(2)-induced effects. These results suggest H(2)O(2) can modulate ICC pacemaker activity and this occur by the activation of K(ATP) channels through PGE(2) production via receptor tyrosine kinase-dependent MAP kinase activation.

Effects of imatinib mesylate in interstitial cells of Cajal from murine small intestine

The interstitial cells of Cajal (ICCs) are pacemakers in the gastrointestinal tract. The possibility of whether imatinib mesylate, a Kit receptor tyrosine kinase inhibitor, modulates pacemaker activities in the ICC was examined using the whole cell patch clamp technique. Imatinib decreased the amplitude of pacemaker potentials in a dose-dependent manner in current-clamp mode. Because the effects of imatinib on pacemaker potentials were the same as those of pinacidil, we examined the effect of glibenclamide on ICC exposed to imatinib. The effects of imatinib on pacemaker potentials were blocked by glibenclamide. To see whether the production of prostaglandins (PGs) is involved in the inhibitory effect of imatinib on pacemaker potentials, we tested the effects of naproxen (a non-selective cyclooxygenase inhibitor) and AH6809 (a prostaglandin EP1 and EP2 receptor antagonist). Naproxen and AH6809 blocked the inhibitory effects of imatinib on ICC. Butaprost (an EP2 receptor agonist) showed the actions on pacemaker potentials in the same manner as imatinib. However, SC 19220 (an EP1 receptor antagonist) has no effects. To investigate the involvement of cAMP and protein kinase A (PKA) in the effects of imatinib on ICC, SQ 22536 (an inhibitor of adenylate cyclase) and mPKAI (an inhibitor of myristoylated PKA) were used. Both SQ-22536 and mPKAI blocked the imatinib-mediated inhibition of pacemaker potentials. However, the protein kinase C (PKC) inhibitors did not block the imatinib-mediated inhibition of pacemaker potentials. These results indicate that imatinib inhibits the pacemaker potentials of ICC by activating ATP-sensitive K(+) channels and PKA-dependent, PKC-independent manner.

Postnatal development of interstitial cells of Cajal in mouse colon in response to Kit signal blockade with Imatinib (Glivec)

This study investigated the response of interstitial cells of Cajal (ICC) in postnatal mouse colon to treatment with Imatinib (Glivec), a potent inhibitor of Kit receptor). ICC were revealed by immunofluorescent staining on frozen cross-sections and whole-mount preparations by anti-Kit and DOG1 antibodies. Kit and p-Kit protein were also evaluated by Western blot. After administration of Imatinib for 4 days beginning at 8 days post-partum (P8), the mean density of Kit+ ICC, which were localized around the myenteric nerve plexus (ICC-MY), within smooth muscle layers (ICC-IM) and in the connective tissue beneath the serosa (ICC-SS), was dramatically decreased to about 50% when compared with controls, but those Kit+ cells located at the submucosal border of circular smooth muscle layer (ICC-SM) seemed to be unchanged in both cell number and morphology. A small number of DOG1+/Kit(-) cells appeared during Imatinib administration. However, these Kit+ ICC were not changed in mice even after 12 days of Imatinib treatment from P24. When Imatinib was discontinued, the number of ICC recovered to normal within 4 days. Our results indicate that the postnatal development of ICC in the mouse colon is Kit dependent, but ICC-SM are unlikely, and the Kit dependence of ICC development is also age-dependent.

Plasticity of interstitial cells of cajal: a study in the small intestine of adult Guinea pigs

Although it is well known that the reduction of interstitial cells of Cajal (ICCs) is associated with several gastrointestinal motility disorders in clinic, it is unknown whether the mature ICCs still have an active plasticity in adult mammals. This study focused on the issues of the reduction of ICCs during Imatinib administration and the recovery of ICCs following drug withdrawal in the small intestine of adult guinea pigs. ICCs were revealed by immunofluorescence on whole mount preparations with anti-Kit, alpha-smooth muscle actin, (alpha-SMA), and 5-bromo-2'-deoxyuridine (BrdU) antibodies. Moreover, the occurrence of apoptosis was also assayed. Imatinib treatment led to a gradual reduction of ICCs in number around the myenteric plexus and deep muscular plexus, which was dependent on the time but no apoptosis of ICCs was detected with the TUNEL method. During Imatinib treatment, some ICC-like cells were double labeled for Kit and alpha-SMA and a few ICC-like cells were only stained with alpha-SMA. When Imatinib was discontinued, the number of ICCs recovered to normal within 32 days. During this time, some proliferating ICCs were demonstrated by double labeling with Kit and BrdU antibodies. Our results indicated that Kit signaling was essential for the maintenance of survival and proliferation of the mature ICCs in the small intestine of adult guinea pigs. Moreover, ICCs might transdifferentiate to a type of alpha-SMA(+) cells, perhaps a phenotype of smooth muscle cells, when there is a loss-of-function of Kit.

Myometrial interstitial cells and the coordination of myometrial contractility

A strict regulation of contractility in the uterus and fallopian tube is essential for various reproductive functions. The uterus contributes, through either increased contractility or periods of relative quiescence, to: (i) expulsion of menstrual debris, (ii) sperm transport, (iii) adequate embryo placement during implantation, (iv) enlarging its capacity during pregnancy and (v) parturition. The dominant cell population of the uterine wall consists of smooth muscle cells that contain the contractile apparatus responsible for the generation of contractile force. Recent interest has focused on a new population of cells located throughout the myometrium on the borders of smooth muscle bundles. These cells are similar to interstitial cells of Cajal (ICC) in the gut that are responsible for the generation of electrical slow waves that control peristalsis. A precise role for myometrial Cajal-like interstitial cells (m-ICLC) has not been identified. m-ICLC express the c-kit receptor, involved in creating and maintaining the ICC phenotype in the gastrointestinal tract. However, both acute and prolonged inhibition of this receptor with the c-kit antagonist imatinib mesylate does not appear to affect the spontaneous contractility of myometrium. Calcium imaging of live tissue slices suggests that contractile signalling starts on the borders of smooth muscle bundles where m-ICLC are located and recently the possible role of extracellular ATP signalling from m-ICLC has been studied. This manuscript reviews the evidence regarding tissue-level signalling in the myometrium with a particular emphasis on the anatomical and possible functional aspects of m-ICLC as new elements of the contractile mechanisms in the uterus.

Expression of C-kit messenger ribonucleic acid and C-kit protein in the gallbladders in guinea pigs of high cholesterol diet

The c-kit protooncogene receptor and its ligand-stem cell factor regulating the proliferation and survival of interstitial cells of Cajal (ICCs) have been described. The aim of this study was to determine the expression of c-kit mRNA and c-kit protein in the gallbladders in guinea pigs of high cholesterol diet (HCD). The gallbladder samples from 16 guinea pigs of HCD and from 16 guinea pigs of standard diet (StD) were used for this study. Expression of c-kit mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR), and expression of c-kit protein was detected by Western blot analysis. Serum total cholesterol (TC) (39 +/- 6 vs. 109 +/- 20 mg/dl), low density lipoprotein (LDL) cholesterol (24 +/- 4 vs. 71 +/- 10 mg/dl), high density lipoprotein (HDL) cholesterol (2.4 +/- 0.4 vs. 7.0 +/- 1.6 mg/dl), and triglyceride (TG) (58 +/- 8 vs. 118 +/- 23 mg/dl) concentrations were significantly higher in the HCD group than in the StD group of guinea pigs (P < 0.001, respectively). Decreased expression of c-kit mRNA was demonstrated in the HCD group compared with the StD group. The ratio of c-kit mRNA and GAPDH was 0.56 +/- 0.09 in controls and 0.50 +/- 0.07 in the HCD group (P = 0.033). C-kit protein expression significantly declined in the HCD group. The mean value of optical density was 129 +/- 25 in the StD group and 103 +/- 19 in the HCD group (P = 0.0009). The data indicate that the expression of c-kit mRNA and c-kit protein significantly decreased in the gallbladders in guinea pigs of HCD.

Uterine contractions depend on KIT-positive interstitial cells in the mouse: genetic and pharmacological evidence

In the gastrointestinal tract, interstitial cells of Cajal (ICCs) generate a pacemaker activity. They produce electric slow waves that trigger and coordinate gut smooth muscle contractions. Interstitial cells of Cajal's slender shape is revealed by KIT immunostaining. Based on several features, including KIT expression and KIT dependence, ICC-like cells were identified in nongastrointestinal tissues. Here, we investigated in the mouse whether uterine contractions depend on ICC-like cells' activity. By labeling KIT-expressing cells, we found putative ICC-like cells in the uterus, observed as KIT-positive interstitial, long spindle-shaped cells with fine branched cytoplasm processes, distributed in muscular layers and in subepithelial connective tissue. We then checked the potential KIT dependence of ex vivo contractile activity of the uterus by combining genetic and pharmacological approaches, using the Kit W-v hypomorphic mutation, and imatinib as a KIT noncompetitive inhibitor. We found a significant reduction in frequency of longitudinal uterine contractions in Kit W-v/Kit W-v compared with Kit+/+ mice, whereas amplitude was unaffected. There was no difference in frequency or amplitude of circular uterine contractions between Kit W-v/Kit W-v and Kit+/+ mice. Ex vivo treatment of Kit+/+ uterine horns with imatinib resulted in a dose-dependent reduction of the frequency and amplitude of longitudinal myometrial contractions. Amplitude and frequency of circular contractions were unaffected in presence of imatinib. These concurrent results suggest that longitudinal contractions of the uterus depend on a KIT signaling pathway of ICC-like cells. The existence of ICC-like cells in the myometrium may enhance our understanding of uterine spontaneous contractile activity and suggest new approaches for treatment of uterine contractility disorders.

Roles of interstitial cells of Cajal in regulating gastrointestinal motility: in vitro versus in vivo studies

The aim of this article is to provide a better understanding of the roles of interstitial cells of Cajal (ICC) in regulating gastrointestinal motility by reviewing in vitro and in vivo physiological motility studies. Based on the in vitro studies, ICC are proposed to have the following functions: to generate slow waves, to mediate neurotransmission between the enteric nerves and the gastrointestinal muscles and to act as mechanoreceptors. However, there is limited evidence available for these hypotheses from the in vivo motility studies. In this review, we first introduce the major subtypes of ICC and their established functions. Three Kit mutant mouse and rodent models are presented and the loss of ICC subtypes in these mutants is reviewed. The physiological motility findings from various in vitroand in vivo experiments are discussed to give a critical review on the roles of ICC in generating slow waves, regulating gastrointestinal motility, mediating neural transmission and serving as mechanoreceptors. It is concluded that the role of ICC as pacemakers may be well established, but other cells may also be involved in the generation of slow waves; the theory that ICC are mediators of neurotransmission is challenged by the majority of the in vivo motility studies; the hypothesis that ICC are mechanoreceptors has not found supportive evidence from the in vivo studies yet. More studies are needed to explain discrepancies in motility findings between the in vitro and in vivo experiments.

Roles of interstitial cells of Cajal in regulating gastrointestinal motility: in vitro versus in vivo studies

The aim of this article is to provide a better understanding of the roles of interstitial cells of Cajal (ICC) in regulating gastrointestinal motility by reviewing in vitro and in vivo physiological motility studies. Based on the in vitro studies, ICC are proposed to have the following functions: to generate slow waves, to mediate neurotransmission between the enteric nerves and the gastrointestinal muscles and to act as mechanoreceptors. However, there is limited evidence available for these hypotheses from the in vivo motility studies. In this review, we first introduce the major subtypes of ICC and their established functions. Three Kit mutant mouse and rodent models are presented and the loss of ICC subtypes in these mutants is reviewed. The physiological motility findings from various in vitro and in vivo experiments are discussed to give a critical review on the roles of ICC in generating slow waves, regulating gastrointestinal motility, mediating neural transmission and serving as mechanoreceptors. It is concluded that the role of ICC as pacemakers may be well established, but other cells may also be involved in the generation of slow waves; the theory that ICC are mediators of neurotransmission is challenged by the majority of the in vivo motility studies; the hypothesis that ICC are mechanoreceptors has not found supportive evidence from the in vivo studies yet. More studies are needed to explain discrepancies in motility findings between the in vitro and in vivo experiments.

Effect of prolonged c-kit receptor inhibition by imatinib mesylate on the uterine contractility of pregnant rabbits

BACKGROUND

The c-kit receptor expressed by interstitial cells in the gastrointestinal tract is crucial to their pacemaking function. The function of similar c-kit-expressing myometrial cells is unknown.

METHODS

Imatinib mesylate, a specific c-kit receptor antagonist, was administered to pregnant New Zealand white rabbits (term = 31 days, n = 35) from day 27 gestation by intramuscular injection twice daily at high (50 microg/kg) or medium (10 microg/kg) dose and compared with a control group injected with vehicle only. In a second phase, two further groups received imatinib at medium or low (1 mug/kg) dose for a longer duration starting from day 18 until delivery. Three does from the latter groups as well as controls underwent myometrial biopsy under general anesthesia after spontaneous vaginal birth. Contractility was recorded by isometric tensiometry. The outcome measures were delay of parturition and in vitro contractility characteristics.

RESULTS

High-dose imatinib induced early delivery when compared with the control group (28.6 vs. 30.7 days, p < 0.001). The other groups delivered at term. No effect on in vitro contractility was apparent in any of the groups.

CONCLUSIONS

c-kit receptor inhibition in pregnant rabbits does not delay significantly the length of gestation or change myometrial contractility in vitro.

Morphological and physiological evidence for interstitial cell of Cajal-like cells in the guinea pig gallbladder

Gallbladder smooth muscle (GBSM) exhibits spontaneous rhythmic electrical activity, but the origin and propagation of this activity are not understood. We used morphological and physiological approaches to determine whether interstitial cells of Cajal (ICC) are present in the guinea pig extrahepatic biliary tree. Light microscopic studies involving Kit tyrosine kinase immunohistochemistry and laser confocal imaging of Ca(2+) transients revealed ICC-like cells in the gallbladder. One type of ICC-like cell had elongated cell bodies with one or two primary processes and was observed mainly along GBSM bundles and nerve fibres. The other type comprised multipolar cells that were located at the origin and intersection of muscle bundles. Electron microscopy revealed ICC-like cells that were rich in mitochondria, caveolae and smooth endoplasmic reticulum and formed close appositions between themselves and with GBSM cells. Rhythmic Ca(2+) flashes, which represent Ca(2+) influx during action potentials, were synchronized in any given GBSM bundle and associated ICC-like cells. Gap junction uncouplers (1-octanol, carbenoxolone, 18beta-glycyrrhetinic acid and connexin mimetic peptide) eliminated or greatly reduced Ca(2+) flashes in GBSM, but they persisted in ICC-like cells, whereas the Kit tyrosine kinase inhibitor, imanitib mesylate, eliminated or reduced action potentials and Ca(2+) flashes in both cell types, as well as associated tissue contractions. This study provides morphological and physiological evidence for the existence of ICC-like cells in the gallbladder and presents data supporting electrical coupling between ICC-like and GBSM cells. The results support a role for ICC-like cells in the generation and propagation of spontaneous rhythmicity, and hence, the excitability of gallbladder.

Interstitial cells of Cajal in dysmotility in intestinal ischemia and reperfusion injury in rats

BACKGROUND

Intestinal ischemia and reperfusion (I/R) injury is an obligatory occurrence in small bowel transplantation. I/R may impair the normal gastrointestinal motility. Interstitial cells of Cajal (ICC) are known as pacemaker cells in the gastrointestinal tract. The aim of this study was to assess the role of ICC in the gastrointestinal motility in a rat model of I/R injury.

MATERIALS AND METHODS

Wistar rats were subjected to 30- or 80-min intestinal ischemia by occluding the mesenteric vessels followed by reperfusion. Small intestinal segments were resected at 12 h or 4 days. The spontaneous mechanical activity was evaluated by organ bath technique. Immunopositivity of c-Kit and PGP9.5 at the level of the myenteric plexus was evaluated as markers of ICC and enteric nerves, respectively.

RESULTS

In the bowel segment with 80-min ischemia followed by 12-h reperfusion, muscles showed a 25% reduction (P < 0.05) in the frequency of contractions compared to that with 30-min ischemia followed by 12-h reperfusion, whereas amplitude of contractions was not significantly different. This change was associated with a 70% decrease (P < 0.01) of c-Kit immunopositivity. These changes of intestinal motility pattern and distribution of c-Kit-positive cells were both recovered from 80-min ischemia followed by 4 days reperfusion. In contrast, the immunopositivity of PGP9.5 was not affected in any I/R injury group.

CONCLUSIONS

Transient functional changes in ICC were induced by prolonged I/R injury but they recovered after 4 days, suggesting a central role of ICC in both disrupting and restoring the normal gastrointestinal motility in I/R injury.

Imatinib inhibits spontaneous rhythmic contractions of human uterus and intestine

The interstitial cells of Cajal (ICC) in the digestive tract and ICC-like cells in extradigestive organs express the c-kit tyrosine-kinase receptor, and have been implicated as pacemakers of smooth muscle spontaneous activity. We used imatinib mesylate (Glivec) to investigate whether c-kit activity of Cajal-like cells in human myometrium is involved in spontaneous rhythmic contractions of human uterine smooth muscle, taking intestinal smooth muscle as a reference tissue. We show that imatinib concentration-dependently inhibited the myogenic contractions of human myometrium in the organ bath, while it significantly affected noradrenaline or K(+)-induced contractions only at concentrations exceeding 50 muM. An inhibitory antibody directed against the extracellular domain of the platelet derived growth factor receptor (PDGFR), another target of imatinib that is expressed by the uterine muscle cells themselves, failed to affect myogenic contractions. These results suggest that Cajal-type cells of human myometrium, as well as ICC of intestinal smooth muscle, participate in myogenic contractile mechanisms, via a novel ligand-independent c-kit/CD117 tyrosine-kinase signaling.

The effect of imatinib mesylate on the contractility of isolated rabbit myometrial strips

BACKGROUND

C-kit receptor expressing interstitial cells generate and coordinate the electrical signals that control peristalsis in the gut. However, the function of interstitial cells in the myometrium is not known.

METHODS

(1) Sections of rabbit myometrium were subjected to immunohistochemical staining for the c-kit receptor. (2) Spontaneously contracting myometrial strips from New Zealand White rabbits near term were mounted in an organ bath and attached to a tension-recording device. The effect of increased concentrations of the c-kit receptor antagonist imatinib mesylate on these contractions was observed. The main outcome measures were the change in frequency, amplitude and duration of contraction.

RESULTS

(1) Multipolar cells expressing c-kit were identified in the fibromuscular septum confirming the presence of interstitial cells in rabbit myometrium. (2) Imatinib decreased the amplitude of contractions by approximately 20% at 100 microM. No effect was seen at lower concentrations. No effect of imatinib on frequency or duration of contractions was observed at any of the concentrations studied.

CONCLUSIONS

In isolated rabbit myometrium, acute inhibition of the c-kit receptor by imatinib mesylate affects only the amplitude of spontaneous contractions at concentrations, the equivalent of x10-100 the normal therapeutic concentration.