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 tubul e PKSV-PR cells and in their multidrug-resistant derivatives PKSV-PRcol50 c ells. 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 [H-3]VBL, 2.7 times larger than that in PKSV-PR cells. Th is flux was partially inhibited by verapamil (VRP) (10 mu M) and cyclospori n A (CsA) (200 nM). [H-3]VBL efflux was also greater in PKSV-PRcol50 than i n 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 [H-3]VBL efflux from PKSV-PRcol50 cells. The cytoplasmic pH (pH(cyt)) of these drug-resistant cells transiently increased in the pr esence of NH4Cl (Delta pH(cyt): +0.4). CCM A caused a moderate, delayed inc rease in pH(cyt) (Delta pH(cyt): +0.1) and made the acidic intralysosomal c ompartment more alkaline (Delta pH(lys): +1.3). VRP and CsA prevented the N H4Cl- and CCM A-induced [H-3]VBL efflux from PKSV-PRcol50 cells. However, V RP (10 mu M) did not significantly affect pH(cyt) of PKSV-PRcol50 cells, th e NH4Cl and CCM A-induced pH(cyt) responses, and the effect of CCMA on pH(l ys). Thus, lysosomotropic agents may affect the kinetics of [H-3]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. (C) 1999 Wi ley-Liss, Inc.