Na+ and K+ transport by the renal connecting tubule

The connecting tubule is emerging as a nephron segment critical to the regulation of Na+ and K+ excretion and the maintenance of homeostasis for these ions. The segment is difficult to study, however, and much of the available information we have concerning its functions is indirect. Here, we review the major transport mechanisms and transporters found in this segment and outline several unsolved problems in the field.Recent electrophysiological and immunohistochemical measurements together with theoretical studies provide a more comprehensive view of ion transport in the connecting tubule. New signaling pathways governing Na+ and K+ transport have also been described.Key questions about how Na+ and K+ transport are regulated remain unanswered. Is the connecting tubule the site of final regulation of both Na+ and K+ excretion? If so, how are the transport rates of these two ions independently controlled?