PROJECT SUMMARY ABSTRACT Women of color are underrepresented in biomedical research and this Diversity Supplement is submitted to mentor Mariani Ramirez to earn a PhD as a pharmacologist. Her project is to look for ways to prevent preterm birth, a major medical problem resulting in disability and death for very preterm infants. Therapeutic approaches to manage preterm labor are off-label and ineffective. No tocolytic therapy in use today is satisfactory beyond 48 hours, and none are FDA approved. Preterm labor more often impacts African American women than their Caucasian counterparts. We seek to understand the dysfunctional relaxation of the myometrium that leads to preterm labor and resulting preterm birth. Our central hypothesis is that nitric oxide is generated locally within the myometrium by microvascular endothelial cells as a result of mechanical stretch and increased blood flow to the expanding uterus. Nitric oxide S-nitrosates Cx43 in the muscle cell. Cx43 S-nitrosation promotes C-terminal phosphorylation that holds Cx43 in its hemichannel state and favors muscle cell quiescence. Hemichannels form gap junctions at the time of labor. Gap junctions are a feature of activated myometrium. Promoting connexin 43 S-nitrosation offers a unique target for tocolytic development. Translational approaches in human pregnancy tissues are essential if we are to discover and exploit the unique mechanisms that subserve uterine quiescence during pregnancy and their dysregulation in preterm labor.