Regulation of [Ca2+]i homeostasis in MRP1 overexpressing cells

Regulation of capacitative Ca2+ entry,vas studied in two different multidrug resistance (MDR) protein (MRP1) overexpressing cell lines, HT29(col) and GLC4/ADR. MRP1 overexpression was accompanied by a decreased response to thapsigargin, Moreover, inhibition of capacitative Ca2+ entry by D,L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) was abolished in MRP1 overexpressing cells. Both PDMP and the MRP1 inhibitor MK571 greatly reduced InsP(3)-mediated Ca-45(2+) release from intracellular stores in HT29 cells. Again, these effects were virtually abolished in HT29(col) cells. Our results point to a modulatory role of MRP1 on intracellular calcium concentration ([Ca2+](i)) homeostasis which may contribute to the MDR phenotype, (C) 2000 Federation of European Biochemical Societies.