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Volume-sensitive chloride channel activity does not depend on endogenous P-glycoprotein
M Tominaga1, T Tominaga, A Miwa
1Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
The Journal of Biological Chemistry
|November 17, 1995
Summary
P-glycoprotein, a drug transporter, does not function as a volume-sensitive chloride channel or regulate it in human intestinal cells. Experiments confirmed its expression but found no link to swelling-activated chloride currents.
Area of Science:
- Cell Biology
- Molecular Biology
- Physiology
Background:
- P-glycoprotein (MDR1 gene product) is a known drug transport pump.
- Its role in regulating volume-sensitive chloride (Cl-) channels remains unclear.
Purpose of the Study:
- To investigate if endogenous P-glycoprotein acts as a volume-sensitive Cl- channel.
- To determine if P-glycoprotein modulates Cl- channels via protein kinase C.
Main Methods:
- Whole-cell patch-clamp electrophysiology in human small intestinal epithelial cells.
- Molecular biology techniques: Northern blot, RT-PCR, Western blot, immunostaining.
- Oligonucleotide treatment, antibody incubation, and pharmacological agents.
Main Results:
- P-glycoprotein expression was confirmed and successfully abolished using MDR1 antisense oligonucleotides.
- No significant difference in swelling-activated Cl- currents was observed between antisense- and sense-treated cells.
- Volume-sensitive Cl- currents were unaffected by P-glycoprotein antibodies, inhibitors (verapamil), substrates (vincristine, daunomycin), or protein kinase C activators.
Conclusions:
- Endogenous P-glycoprotein is not a volume-sensitive Cl- channel in human epithelial cells.
- P-glycoprotein does not function as a protein kinase C-mediated regulator of these channels.