HYPOTONICITY-INDUCED ANION FLEXES IN CELLS EXPRESSING THE MULTIDRUG-RESISTANCE-ASSOCIATED PROTEIN, MRP

Anion transport in human multidrug-resistant large cell lung tumour ce lls (COR-L23/R) which overexpress the multidrug-resistance-associated protein (MRP) has been compared with that in cells of the parent line (COR-L23/P). Whole-cell patch-damp recordings reveal variability betwe en individual cells in basal anion conductance and in anion conductanc e increases following exposure to hypotonic media. The increase of sti mulated over basal conductance is significantly larger for resistant c ells than for parent cells. The chloride channel blocker, diisothiocya natostilbene-2-2'disulphonic acid (DIDS), rapidly and reversibly inhib its the increase in outward but not inward conductance when applied ex ternally at 10(-4) M during recording, but it is without effect when i ntroduced into the cells via the patch pipette. Preincubation with DID S greatly reduces both inward and outward conductance. I-125(-) efflux has been used to measure anion movement in cell populations. Basal ef flux is similar in the two cell lines, but following a hypotonic chall enge, the increase in rate constant for efflux from COR-L23/R cells is at least double that from COR-L23/P cells. This increase in efflux is greatly reduced by incubation with DIDS at 10(-4) M. Replacement of e xternal chloride by gluconate does not affect efflux, thus excluding t he possible involvement of DIDS-sensitive chloride exchange, Results f rom both techniques suggest that DIDS-sensitive, hypotonicity-induced anion channel activity is augmented in COR-L23/R multidrug-resistant v ariant cells which overexpress MRP. This augmentation may be caused by MRP itself or by other genes coexpressed with MRP.