Question

The goal of the investigation presented in this case was to determine the mechanism for lactate
transport in the liver. Lactate is a major substrate for gluconeogenesis, but its transport from the blood to
liver cells is incompletely understood. Lactate transport is physiologically important because the
conversion of lactate to glucose in the liver as part of the Cori cycle requires that lactate released from
the muscle during anaerobic fermentation be transported to the liver via the bloodstream. Previous studies
have indicated that the transport of lactate is probably mediated by a carrier protein, but it was not
understood exactly how the carrier worked. For example, it was not known whether lactate transport was
linked to the transport of other ions such as H or OH . In the experiments presented here, investigators + -
measured the rate of uptake of [ C]-labeled lactate in rat hepatocytes under a variety of different physiological conditions. In this manner, the characteristics of the lactate transporter were determined.

1)The investigators considered the possibility that lactate did not have its own transporter, but instead
used the general anionic transporter in liver cells. In order to test this hypothesis, they measured the
uptake o 2 4
f 0.4 mM [ C] lactate in the presence of 10 mM Na SO and found that lactate transport 14
was 2 4
inhibited 11% in the presence of the Na SO . (The sulfate ion is transported by the general
anionic transporter.) Do these results indicate that lactate utilizes the general anionic transporter? Explain.

Answer 1

The experiments do help us to know that lactate can be transported through anion transporter as there is a reduction in transport of (SO₄)^2- ions from the same region like lactate transporter in presence of lactate. But the experiment does not give us any information about the specificity of the transporter. A better experiment would be to block anion tranporters using a small molecule or a blocking antibody and test whether lactate is transported into the hepatocytes of rat liver.