MODULATION OF SODIUM-COUPLED UPTAKE AND MEMBRANE FLUIDITY BY CISPLATIN IN RENAL PROXIMAL TUBULAR CELLS IN PRIMARY CULTURE AND BRUSH-BORDER MEMBRANE-VESICLES

The proximal tubule appears to be the main target for the adverse effe cts of cis-diamminedichloroplatinum (II) (cDDP). We evaluated the earl y effects of cDDP at concentrations (3 to 67 mu M) lower that those wh ich alter cell viability, on three apical transport systems and on the physical state of the brush border membrane (BBM) in rabbit proximal tubule (RPT) cells in primary culture. The maximal effect, correspondi ng to a 30% decrease in Na+-coupled uptake of phosphate (Pi) and alpha -methylglucopyranoside (MGP) and a twofold increase in Na+-coupled ala nine uptake, was obtained at 17 mu M (5 mu g/ml) cDDP and occurred thr ough a modification of their affinity. At this concentration, cDDP inc reased BBM fluidity and decreased the BBM cholesterol content by 28%, without increasing the permeability of tight junctions. To clarify the role of cDDP-induced increase in BBM fluidity on alterations of Na+-c oupled uptake, these parameters were also investigated in BBM vesicles isolated from rabbit renal cortex directly exposed to cDDP. cDDP indu ced a concentration-dependent inhibition of Na+-coupled uptake of MGP, Pi and alanine in BBM vesicles from the renal cortex, associated with a decrease in protein sulfhydryl content, without modifying BBM fluid ity. Our findings strongly suggest that the cDDP-induced increase in B BM fluidity in RPT cells results from an indirect mechanism, possibly an alteration of cholesterol metabolism and did not play a major role in the cDDP-induced inhibition of Na+/Pi and Na+/glucose cotransport s ystems that may be mainly mediated through a direct chemical interacti on with essential sulfhydryl groups of the transporters.