Cristina Vidulescu*, C.M. Țigaret*, D.E. Deleanu, L.M. Popescu*
*Dr. Cristina Vidulescu, Dr. CM. Tigaret, Dr. D.E. Deleanu, Prof Dr.L.M. Popescu. Catedra de Biologie Celulară și Histologie, UM.F. “Carol Davila”, București
Abstract
The molecular mechanism of smooth muscle myogenic rhytmic contractions are still not known. The rationale of this study was to test the possible involvement of a postuleted basal activity of signaling systems in myogenic contractions mechanism. since these contractions are not elicited by agonists. In this case we investigated the role of phospholipase c. We used polyclonal inhibitory anti-phospholipase c antibodies as specific inhibitors of phospholipase c activity. Antibodies against phosphatidylinositide-specific phospholipase c and phosphatidylcholine-specific phospholipase c. respectively, diminished myogenic rhytmic contractions of human myometrial strips “in vitro”, while exogeneously added phospholipase c enhanced them. Inositol 1.4.5-triphosphate-containing liposomes induced in the myometrial strips short-lived (30-60 s) oscillatory contractions similar to the agonist-induced oscillatory contractions and had no effect if the myogenic contractions were already present. LiCI (15 mM) had no effect on myogenic contractions of human myometrium. These results suggest the inositol 1.4.5-triphosphate sensitive Ca2+-pool may be involved in rhytmic contractions mechanism. Proteinkinase C activators 1-oleoyl 2-acetyl glycerol (20 µ M). 12-O-tetradecanoyl phorbol 13-acetate (50 nM) and phorbol 12,13-dibutyrate (200 nM) were able to induce sustained rhytmic contractions in silent myometrial strips or to enhance myogenic rhytmic contractions. Different protein kinase C inhibitors diminished or abolished myogenic contractions. These inhibitors were: H-7 (10 µ M). H-8 (50 µ M). HA-1004(20µ M). as well as: polymyxin B (20 µM). palmitoyl carnitine (46 uM). tamoxifen (200 µM). phloretin (160 µ M). sphingosine (300 µ M). In conclusion. protein kinase C is crucially involved in generating and/or maintaining myogenic contractile activity. Phospholipase C basal activity is needed for full development of rhytmic myogenic contractions.