title: Failure of P-glycoprotein (MDR1) expressed in Xenopus oocytes to produce swelling-activated chloride channel activity.
abstract: 1. P-glycoprotein, the protein product of the multidrug resistance (MDR1) gene, has ATP-dependent transporter activity. It has been suggested that P-glycoprotein may also function as a volume-regulated chloride channel or chloride channel regulator. To assess the chloride channel function of P-glycoprotein, we examined swelling-activated chloride conductances in Xenopus oocytes injected with human MDR1 cRNA. 2. Functional expression of P-glycoprotein in Xenopus oocytes was confirmed using Western blot analysis and by assessing transport of the P-glycoprotein substrate, calcein AM. 3. Endogenous, swelling-activated chloride conductances were virtually absent by the time P-glycoprotein expression was confirmed. Thus, this expression system afforded the advantage of assessing putative MDR1-associated chloride currents in the absence of background currents. 4. The currents activated by hypotonic shock (50%) in both MDR1-injected and control (water-injected) oocytes were not significantly different. The swelling response was due in part to the activation of a potassium-selective conductance which could be inhibited by barium. No chloride-selective currents were activated by hypotonic shock in the presence or absence of barium. Therefore, we conclude that P-glycoprotein expression does not produce a swelling-activated chloride conductance in the Xenopus oocyte expression system.
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis / Q000494:pharmacology*; D000818:Animals; D017609:Barium Compounds / Q000494:pharmacology; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D007038:Hypotonic Solutions; D009865:Oocytes / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis; D013050:Spectrometry, Fluorescence; D014982:Xenopus laevis
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017609:Barium Compounds; D018118:Chloride Channels; D002712:Chlorides; D007038:Hypotonic Solutions; C024986:barium chloride; D012313:RNA