CHARACTERIZATION OF RENAL BRUSH-BORDER AND BASOLATERAL MEMBRANE TRANSPORTERS FOR ORGANIC CATIONS

The renal proximal tubule is the site of active secretion of a diverse array of organic cations and bases (collectively, OCs). The basolater al entry step in trans-tubule OC transport involves an electrogenic fa cilitated diffusion process. OC exit into the tubule lumen is the acti ve step in secretion and involves the carrier-mediated exchange of OC for H+. The specificity of these two processes is influenced less by s teric characteristics of substrates than by their chemical lipophilici ty, with both transporters displaying an increasing affinity for OCs o f increasing lipophilicity. Several additional OC transporters exist w ithin each membrane and the concerted activity of these processes perm its the proximal tubule to effect the secretion of most OCs, and the s elective reabsorption of others, and provides the tubule with a degree of 'redundancy' in the means available for secreting potentially toxi c xenobiotic compounds from the body.