Inhibition of P-glycoprotein-mediated transport by a hydrophobic contaminant in commercial gluconate salts.
The substitution of gluconate for Cl- is commonly used to characterize Cl- transport or Cl--dependent transport mechanisms. We evaluated the effects of substituting gluconate for Cl- on the transport of the P-glycoprotein substrate rhodamine 123 (R123). The replacement of Ringer solution containing Cl- (Cl--Ringer) with gluconate-Ringer inhibited R123 efflux, whereas the replacement of Cl- by other anions (sulfate or cyclamate) had no effect. The inhibition of R123 efflux by gluconate-Ringer was absent after chloroform extraction of the sodium gluconate salt. The readdition of the sodium gluconate-chloroform extract to the extracted gluconate-Ringer or to cyclamate-Ringer inhibited R123 efflux, whereas its addition to Cl--Ringer had no effect. These observations indicate that the inhibition of P-glycoprotein-mediated R123 transport by gluconate is due to one or more chloroform-soluble contaminants and that the inhibition is absent in the presence of Cl-. The results are consistent with the fact that P-glycoprotein substrates are hydrophobic. Care should be taken when replacing ions to evaluate membrane transport mechanisms because highly pure commercial preparations may still contain potent contaminants that affect transport.
Vanoye
C G
CG
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-0641, USA.
Altenberg
G A
GA
Reuss
L
L
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000502:physiology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D002725:Chloroform; D006224:Cricetinae; D003412:Cricetulus; D004338:Drug Combinations; D004340:Drug Contamination; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D005942:Gluconates / Q000737:chemistry / Q000494:pharmacology*; D007552:Isotonic Solutions / Q000494:pharmacology; D020112:Rhodamine 123 / Q000493:pharmacokinetics; D000077331:Ringer's Solution
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002614:Chelating Agents; D004338:Drug Combinations; D005456:Fluorescent Dyes; D005942:Gluconates; D007552:Isotonic Solutions; D020112:Rhodamine 123; D002725:Chloroform; D000077331:Ringer's Solution; D002118:Calcium