Complex effects of imatinib on spontaneous and oxytocin-induced contractions in human non-pregnant myometrium

Human myometrium includes two important cell populations involved in its contractility: smooth muscle fibers and interstitial cells. The pacemaking mechanism is not yet identified, but it is possible that myometrial smooth muscle cells contract in response to a signal generated by c-kit positive interstitial cells. The aim of this study was to investigate the effects of imatinib as a c-kit receptor antagonist on the spontaneous or oxytocin (OT) induced contractions of human non-pregnant myometrium in vitro. Myometrial strips were obtained from non-pregnant women (reproductive age) undergoing hysterectomy for benign indications. The strips were suspended in organ baths for recording of isometric tension. Imatinib effects were assessed on spontaneous contraction and after preexposure to OT. Direct exposure of myometrial strips to imatinib inhibits both amplitude and frequency of contractions (80-320 mu M) in a dose dependent manner. Amplitude reverted back to 90% of the baseline amplitude by consequent addition of imatinib (until 480 mu M). Total inhibition of myometrial contraction was obtained after addition of OT 60 nM. If myometrium was pre-exposed to OT (320 nM), imatinib 80-160 mu m increased amplitude, while decreasing frequency. These data provide evidence that telocytes may be involved as modulators of the spontaneous contractions of the non-pregnant human uterus, via a tyrosine-kinase independent signaling pathway.