P2X receptors are a family of seven ligand-gated cation channels (LGCCs) that use the energy of ATP binding to initiate a depolarizing flux of cations across cell membranes. Calcium ions carry a disproportionately large percentage of this current, and P2X receptors have one of the largest Ca2+ fluxes of all LGCC families. The resulting rise in intracellular Ca2+ evokes transmitter release from central and peripheral neurons and glia, promotes hormone release from endocrine glands, triggers contraction of muscle, regulates airway ciliary motility, and activates downstream signaling cascades in a variety of cells. ATP has multiple effects on the cardiovascular system. Hematopoietic cells (P2X7), blood vessels (P2XO, and the heart (P2X!.7) all express P2X receptors, and in many cases, the actions of ATP on these tissues are linked to Ca2+ influx. For example, over-expression of the P2X4 receptor enhances cardiac performance and prolongs survival in a transgenic mouse model of heart failure by elevating resting Ca2+ and enhancing basal cardiac contractility. Nature itself may use a similar approach, as P2X receptors are upregulated in the hearts of human patients suffering from dilated cardiomyopathy. Manipulation of endogenous P2X receptors may therefore represent a new therapeutic approach for the treatment of cardiac disease. The focus of our laboratory is the study of the molecular physiology of recombinant P2X receptors. We are particularly interested in describing the mechanics of ATP-gated Ca2+ transport across the membrane and understanding how ATP opens the pore. In this proposal, we outline experiments that build upon our previous work to provide a more quantitative description of the events that follow ATP binding. Relevance to public health: Our work is relevant because it provides the missing information needed to better understand the role that ATP plays in health and sickness. This is important because the receptors may present a new and potentially exciting means of increasing the rate of survival of patients affected by a number of cardiovascular diseases including hypertension and heart failure.