The cyclic nucleotides cAMP and cGMP play key roles in cellular signaling and the
extracellular regulation of fluid balance. In the kidney, cAMP is excreted across the apical
proximal tubular membrane into urine, where it reduces phosphate reabsorption through a
dipyridamole-sensitive mechanism that is not fully understood. It has long been known that
this cAMP efflux pathway is dependent on ATP and is inhibited by probenecid. However, its
identity and whether cGMP shares the same transporter have not been established. Here …