This is achieved by transporters that have higher affinity for K+ than for Na+ at the level of influx, by efficient efflux of toxic or surplus cations from the cells, and also by selective compartmentalisation of cations in organelles (reviewed in [ 19]).
The wine S. cerevisiae strains are more resistant to SO2, which has been a widely used preservative for centuries, due to higher SSU1 gene expression, which encodes a plasma membrane sulfite pump that is required for efficient sulfite efflux and maintains sufficiently low sulfite levels to prevent toxicity (Park and Bakalinsky [2000]).
The intracellular Se0 granules strongly suggest that selenite tolerance of strain Sm777 is not related to an efficient efflux system.
Moreover, as shown for their normal counterpart, CSCs have been proposed to exhibit high level expression of multidrug transporter family genes, likely resulting in more efficient efflux of chemotherapeutic drugs and innate multidrug resistance, In addition, signaling pathways, such as Wnt, Hedgehog or Notch, are dysregulated in CSCs leading to tumor development.
Alternatively, CAT8 may participate to exude Gln from the tip to attract beneficial micro-organisms, although the high affinity may argue against an efficient efflux capacity [32].
The presence of SmAQP in the tegument of the worms assures an efficient efflux of lactate from the animals to the host-medium.
Disturbance of copper homeostasis and ensuing oxidative stress may impede the efficient efflux of iron by caeruloplasmin.
This rapid and efficient efflux is similar to that of the Pgp substrate Rho123 from mitochondria of a drug-resistant hepatocellular carcinoma cell line (Solazzo et al, 2006).
Therapeutic resistance in pancreatic cancer is caused by low permeability of the tumour micro-environment, as well as by the efficient efflux of toxic agents [ 3, 4].
Nonetheless, yeast appears to tolerate the high-level of artemisinic acid by operating its efficient efflux pumps, such as the ABC transporters.
