LYSOSOMOTROPIC AGENTS INCREASE VINBLASTINE EFFLUX FROM MOUSE MDR PROXIMAL KIDNEY CELLS EXHIBITING VECTORIAL DRUG TRANSPORT

Vinblastine (VBL) transport and efflux were studied in mouse proximal tubule PKSV-PR cells and in their multidrug-resistant derivatives PKSV-PRcol50 cells. The PKSV-PRcol50 cells produced more mdr1b transcripts and had higher resistance to various drugs. PKSV-PRcol50 cells had a predominantly basal-to-apical flux of [3H]VBL, 2.7 times larger than that in PKSV-PR cells. This flux was partially inhibited by verapamil (VRP) (10 μM) and cyclosporin A (CsA) (200 nM). [3H]VBL efflux was also greater in PKSV-PRcol50 than in PKSV-PR cells. Treatment with NH4Cl (30 mM), a lysosomotropic weak base, and concanamycin A (CCM A) (20 nM), an inhibitor of the vacuolar H+/ATPase, further increased [3H]VBL efflux from PKSV-PRcol50 cells. The cytoplasmic pH (pHcyt) of these drug-resistant cells transiently increased in the presence of NH4Cl (ΔpHcyt: +0.4). CCM A caused a moderate, delayed increase in pHcyt (ΔpHcyt: +0.1) and made the acidic intralysosomal compartment more alkaline (ΔpHlys: +1.3). VRP and CsA prevented the NH4Cl- and CCM A–induced [3H]VBL efflux from PKSV-PRcol50 cells. However, VRP (10 μM) did not significantly affect pHcyt of PKSV-PRcol50 cells, the NH4Cl- and CCM A–induced pHcyt responses, and the effect of CCMA on pHlys. Thus, lysosomotropic agents may affect the kinetics of [3H]VBL efflux. Our results also suggest that the inhibitory action of VRP on VBL efflux was not directly mediated by a pH-dependent process in these drug-resistant renal proximal tubule cells. J Cell Physiol 178:247–257, 1999. © 1999 Wiley-Liss, Inc.