Protein kinase C-independent correlation between P-glycoprotein expression and volume sensitivity of Cl- channel.
The possible correlation between P-glycoprotein (PGP) and volume-sensitive Cl- channel was examined in a pair of cell lines: a subline of the human epidermoid KB cell (KB-3-1) and the corresponding MDR1-transfected cell line (KB-G2). Western blot analysis and indirect immunofluorescence studies indicated that KB-G2, but not KB-3-1, exhibits the PGP expression. Patch-clamp whole-cell recordings showed that osmotic swelling activates Cl- currents not only in PGP-expressing but also in PGP-lacking cells. The amplitude of the maximal current was indistinguishable between both cells. Activation of protein kinase C (PKC) or loading with a PKC inhibitor failed to affect the swelling-induced activation of the Cl- currents in both cells. The relation between whole-cell Cl- currents and cell size measured simultaneously showed that volume sensitivity of the Cl- channel was augmented by the PGP expression irrespective of the activity of PKC on the plasma membrane. A similar increase in volume sensitivity of the Cl- channel was also induced by the expression of the ATP hydrolysis-deficient PGP mutant, K433M. We conclude that P-glycoprotein does not represent the volume-sensitive Cl- channel but that its expression modulates volume sensitivity of the Cl- channel in a manner independent of its ATPase activity or of the protein kinase C activity.
Miwa
A
A
Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki 444, Japan.
Ueda
K
K
Okada
Y
Y
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis*; D018118:Chloride Channels / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D015640:Ion Channel Gating; D017136:Ion Transport; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018118:Chloride Channels; D011493:Protein Kinase C