Doxorubicin selection for mdr/p-glycoprotein reduces swelling
-activated k+ and cl- currents in mes-sa cells.
Luckie, Douglas B., Mauri E. Krouse, Tina C. Law, Branimir I. Sikic,
and Jeffrey J. Wine.
Cystic Fibrosis Research Laboratory, Medicine/Oncology, Stanford
University, Stanford, CA 94305
APStracts 2:0370C, 1995.
To test the hypothesis that P-glycoprotein (P-gp) enhances swelling
currents through regulation of volume sensitive chloride channels
(recently termed VSOAC), a human uterine sarcoma cell line (MES-SA)
and its doxorubicin-selected counterpart (Dx5) were studied. P-gp
mRNA and protein levels were detected only in Dx5 cells. However,
whole-cell patch clamp experiments showed that swollen Dx5 (n=5)
cells produced smaller VSOAC currents than MES-SA (n=4) cells (106
+/-26 pA/pF vs. 232 +/-76 pA/pF@90mV). In radioisotopic efflux
experiments both swelling-activated 125I (Cl-) currents (n=15) and
86Rb (K+) currents (n=8) were found to be 2-4 fold smaller in the Dx5
(high P-gp) cells. Inhibitors of P-gp showed no specificity for the
doxorubicin-selected cells (Dx5). 100uM dideoxyforskolin blocked
swelling-activated 125I efflux equally in both cell lines, while
100uM verapamil had no effect. Thus, in this cell line, selection for
P-glycoprotein expression is associated with reduced swelling
currents. These findings suggest that P-glycoprotein expression does
not directly facilitate VSOAC.
Received 20 July 1995; accepted in final form 22 September 1995.
APS Manuscript Number C440-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95