Lactate, efflux transport

Recent evidence suggests that excretion of ochratoxin A into human milk is mediated by breast cancer resistance protein (BCRP). BCRP is a member of the ATP-dependent efflux transporter family, which is highly expressed during lactation in various species, including humans, and is known to be responsible for the excretion of various drugs and xenobiotics into milk (Jonker et al., 2005 Schrickx... 

Secondly, the transport inhibitor must be able to pass the cell membrane. The inability of benzene-1,2,3-tricarboxylate to inhibit gluconeogenesis from lactate in perfused pigeon liver, a tissue in which mitochondrial efflux of phosphoenolpyruvate is obligatory for glucose synthesis, is presumably due to lack of penetration through the plasma membrane [16], This observation is interesting since it shows that the ability of an inhibitor to penetrate the cell membrane may vary from tissue to tissue benzene-1,2,3-tricarboxylate does inhibit lipogenesis in hepatocytes of neonatal chicks, as discussed above. Another example is the apparent relative impermeability of the plasma membrane of isolated foetal rat hepatocytes, as compared with that from adult rats, for atractyloside, the inhibitor of the adenine nucleotide translocator [17]. 

Mitochondrial aspartate efflux is important in processes like urea synthesis [90], gluconeogenesis from lactate and the transport of cytosolic reducing equivalents to the mitochondria via the so-called malate-aspartate shuttle, e.g. during ethanol oxidation and gluconeogenesis from reduced substrates like glycerol, sorbitol, and xylitol [4,5]. During gluconeogenesis from lactate oxaloacetate is transported to the cytosol as aspartate to circumvent the low permeability of the mitochondrial membrane for oxaloacetate. 

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