Role of calcium in chloride-secreting epithelia.

There are a number of well-characterized chloride-secreting epithelia. The role of cyclic AMP in mediating chloride secretion in these tissues is well established. The role of calcium is less well established, although a substantial body of evidence points to a significant mediator role of calcium in the modulation of chloride secretion. In some of these tissues, a rise in cytosolic calcium activity in response to secretagogues may potentiate cyclic AMP effects on chloride conductance by the activation of serosally located potassium channels. In addition, in many instances, the effect of a rise in cytosolic calcium may itself be mediated by stimulation of cyclooxygenase products that themselves are known to be chloride secretagogues. Sustained chloride secretion may reflect a synergism between cyclic AMP, calcium, and prostaglandins although such a mechanism is apparent in only some but not all chloride-secreting epithelia. It is hoped that with the application of newer techniques to measure cytosolic calcium concentration and to monitor individual channel activities, we will better understand the exact role of calcium in modulating chloride transport.