title: Alterations in respiration rate of isolated rainbow trout hepatocytes exposed to the P-glycoprotein substrate rhodamine 123.
abstract: Reducing intracellular xenobiotic concentration is an important defence strategy used by cells challenged with foreign chemicals. One mechanism used to achieve this goal is via the use of P-glycoproteins (P-gps), ATP-dependent transporters that mediate the removal of hydrophobic compounds from cells. The energetic costs of this mechanism are unknown, therefore, the activity and respiratory costs associated with the P-gp-mediated efflux of rhodamine 123 (R123) was measured in isolated rainbow trout hepatocytes. The accumulation of R123 was rapid and concentration-dependent. Initial accumulation rates were 1.79+/-0.41, 7.29+/-1.06 and 15.30+/-1.74ngR123/min/10(6)cells when exposed to 1, 5 and 10 microM R123, respectively. Efflux was measured in cells 'pre-loaded' with R123 at each concentration, resulting in initial efflux rates of 0.77+/-0.12, 2.02+/-0.35 and 3.51+/-0.84ngR123/min/10(6)cells, respectively. The baseline oxygen consumption rate of hepatocytes was 33.21+/-1.09 ng O2/min/10(6)cells. Respiration rates were significantly higher in cells exposed to 5 and 10 microM R123 (39.08+/-0.80 and 41.72+/-0.61ng O2/min/10(6)cells), representing increases over basal rates of 18.5 and 25.7%, respectively. Measurements of isolated mitochondrial respiration established that changes in hepatocyte oxygen consumption were not through the direct effects of R123 on mitochondria. The P-gp inhibitor, XR9576 significantly inhibited R123 efflux from cells with a concomitant return of respiration rates to baseline values. This study demonstrates that increased P-gp transport of xenobiotics can significantly raise cellular respiration rates and may result in higher energy costs for organisms living in P-gp-substrate contaminated environments.
authors: Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6.
authors: Onkar S
authors: OS
authors: Bains
authors: Christopher J
authors: CJ
authors: Kennedy
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004734:Energy Metabolism; D005260:Female; D022781:Hepatocytes / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D010101:Oxygen Consumption; D020112:Rhodamine 123 / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D020112:Rhodamine 123