Alcohol intoxication complicates injury and infection by impairing cardiovascular function, fluid homeostasis, and host defense. The lymphatics of the gut are a multifunctional transport system that normally serves as a delivery and surveillance system for potentially harmfull antigens, optimizing mucosal innate and adaptative immunity. Alcohol increases mesenteric lymph flow, which could potentially be harmful if gut barrier function is compromised, such as after traumatic injury. In such cases increased lymph flow could facilitate delivery of an overwhelming number of pathogens to the lymph node barrier, allowing entry to the systemic circulation, and infection of the heart, lungs and other organs. We recently showed that alcohol modulates the intrinsic contractile cycle of mesenteric lymphatics that provides the driving force for lymph flow. We aim to discover the molecular mechanisms by which alcohol enhances intrinsic lymphatic pumping. Because of the known importance of Ca2+ in smooth muscle contraction, we developed a novel method to measure cytosolic [Ca2+] in isolated rat collecting lymphatics. Our preliminary data indicate that alcohol modulates phasic contractions of lymphatic vessels by decreasing the frequency yet increasing the magnitude of cyclic mobilizations of Ca2+ from internal stores. Alcohol also inhibits the lymphatic myogenic constriction in response to increases in luminal pressure. However, alcohol does not inhibit the associated gradual increase in cytosolic [Ca2+] during the diastolic phase of the contractile cycle, which suggests that the inhibition of myogenic constriction may instead be due to impaired sensitivity to Ca2+. We hypothesize that alcohol decreases the frequency and increases the magnitude of Ca2+ mobilization in lymphatic smooth muscle to cause less frequent but larger contractions, and in addition decreases mesenteric lymphatic tone by inhibiting Ca2+-sensitizing mechanisms. We will test this hypothesis with two Specific Aims: 1) to test the prediction that acute alcohol intoxication induced-changes in the lymphatic phasic contraction pattern are caused by an altered cyclic mobilization of Ca2+, and 2) to demonstrate that alcohol intoxication inhibits Ca2+ sensitization in lymphatic smooth muscle, causing a decrease in tone and loss of myogenic responsiveness. We will utilize an established rat model of acute alcohol intoxication in combination with our novel method to simultaneously track changes in cytosolic [Ca2+] and intrinsic pump function in isolated mesenteric lymphatics. In addition, pharmacological interventions will be combined with biochemical analyses of key signaling molecules to determine the underlying Ca2+- dependent and Ca2+-sensitizing mechanisms impacted by alcohol intoxication. The successful completion of these studies will reveal the lymphatic contractile mechanisms impacted by alcohol intoxication, this will advance our knowledge on how alcohol intoxication disrupts immunity in the digestive tract. This information will also enable development of useful therapeutic strategies to prevent infections that hamper cardio- pulmonary function in alcohol-intoxicated trauma victims.