Selection for MDR1/P-glycoprotein enhances swelling-activated K+ and Cl- currents in NIH/3T3 cells.
The relationship between multidrug resistance (MDR) P-glycoprotein expression and swelling-activated Cl- and K+ conductance was investigated in mouse NIH/3T3 fibroblasts and their colchicine-selected counterparts (COL1000, high P-glycoprotein). Whole cell patch-clamp and isotopic flux experiments confirmed that swelling-activated Cl- currents were induced by 20-30% bath dilution only in the MDR-expressing cell line. However, at bath dilutions > 30%, both cell lines developed Cl- currents that reached similar large magnitudes at higher dilution levels. Thus the apparent absolute difference in cell lines at lower dilutions is due to a shift in the response curve relating hypotonicity to Cl- conductance. At all dilutions and in both cell lines, the swelling-activated Cl- currents were outwardly rectifying, active at negative cell voltages, and inactivated at positive voltages. Verapamil (100 microM) and 1,9-dideoxyforskolin (100 microM), which inhibit P-glycoprotein drug transport, did not significantly inhibit the swelling-activated Cl- conductance efflux in the COL1000 cells also showed a leftward shift in the response curve to hypotonicity. These results indicate that response curve to hypotonicity. These results indicate that colchicine-selection for increased P-glycoprotein expression did not lead to the expression of swelling-activated Cl- channels, but instead enhanced a step in the pathway from bath dilution to regulatory volume decrease that is common to both K+ and Cl- channels.
Luckie
D B
DB
Cystic Fibrosis Research Laboratory, Stanford University, California 94305-2130.
Krouse
M E
ME
Harper
K L
KL
Law
T C
TC
Wine
J J
JJ
D016475:3T3 Cells / Q000502:physiology; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D000838:Anions / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology*; D002460:Cell Line; D002712:Chlorides / Q000502:physiology*; D003078:Colchicine; D004487:Edema / Q000503:physiopathology*; D004553:Electric Conductivity; D004594:Electrophysiology; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology; D007038:Hypotonic Solutions / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D051379:Mice; D011188:Potassium / Q000502:physiology*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000838:Anions; D002352:Carrier Proteins; D002712:Chlorides; D007038:Hypotonic Solutions; D008562:Membrane Glycoproteins; D011188:Potassium; D003078:Colchicine