Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC343

Poster Communications

Tissue-specific responses of human uteroplacental smooth muscles to Ca2+/calmodulin-dependent kinase II inhibition

M. Sweeney1, S. C. Robson1, M. J. Taggart1

1. Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom.

Successful development of the human fetus during pregnancy depends on tight regulation of the uterine and placental vasculatures in order to allow appropriate exchange of oxygen and nutrients from the mother to the placenta. We have previously identified differences in modes of regulation of myometrial versus placental blood vessel function (1, 2) that may be indicative of generic differences in the behaviour of smooth muscle-rich tissues of the human uteroplacental environment. Decoding of the Ca2+ signals that underlie smooth muscle contractility may involve not only the archetypal pathway of Ca2+/calmodulin-dependent myosin light chain kinase activation but also ancillary Ca2+-sensitive kinases, such as the multifunctional Ca2+/calmodulin-dependent kinase II (CaMKII). Therefore, the aim of this study was to compare the relative effect of pharmacological inhibition of CaMKII on contractility of human myometrial arteries (MA), placental arteries (PA) and myometrium (M). Myometrial and placental biopsies were obtained from women undergoing elective Caesarean section, following delivery of a singleton infant from a full term healthy pregnancy. Small (<500µm diameter) MA and chorionic plate PA were dissected, cut into 2mm rings and mounted on a wire myograph for recording of isometric force development. Myometrial strips (~0.2X0.5mm) were mounted isometrically in organ baths. All tissues were constricted with high potassium (60mM) depolarising solution (KPSS) or agonist (thromboxane A2 agonist U46619 (1µM) in arteries, oxytocin (10nM) in M) for 30 minutes, then relaxed in physiological salt solution. Following incubation with the CaMKII inhibitor KN93 (0.3-20µM), or its’ inactive analogue KN92 or vehicle, for 30 minutes, tissues were re-exposed to KPSS or agonist. Fold change in constriction was determined for each tissue and group mean±SEM calculated. In all tissues, incubation with KN93 significantly reduced constrictions in a concentration-dependent manner (P<0.01, ANOVA). The efficacy of inhibition by KN93 was significantly greater in MA than PA with both greater than in M (P<0.01, 2 way ANOVA). With maximum KN93 concentration, KPSS-induced constrictions in MA were effectively abolished (n=7) compared with PA (decreased to 0.19±0.04 fold, n=6) and M (0.84±0.10 fold, n=5). Maximum concentration of KN92 caused only a small reduction in arterial constriction which was significantly less than that with KN93. Inhibition of agonist-induced constriction by KN93 in arteries (MA 0.41±0.01 fold, n=4, PA 0.75±0.01 fold, n=4), but not in M (0.69±0.04 fold, n=5), was significantly less (P<0.01) than the reduction in KPSS-induced constriction. These tissue-specific responses to CaMKII inhibition add to our increasing awareness of differential mechanisms of regulation of tone between human myometrial and placental arteries and myometrial tissue.

Where applicable, experiments conform with Society ethical requirements