Leucine-proton cotransport system in Chang liver cell

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Transport

Background:

• The transport of amino acids across cell membranes is crucial for cellular function.
• Understanding the mechanisms of amino acid uptake, particularly L-leucine, is important for liver cell physiology.

Purpose of the Study:

• To investigate the role of proton gradients in L-leucine uptake by Chang liver cells.
• To elucidate the relationship between amino acid transport and pH changes in the plasma membrane.

Main Methods:

• Utilized plasma membrane vesicles from Chang liver cells to study L-leucine uptake kinetics.
• Measured intravesicular acidification and cytoplasmic pH changes in response to L-leucine and proton gradients.
• Investigated the effect of sodium (Na+) and amiloride on L-leucine uptake and pH dynamics.

Main Results:

• An inward proton gradient increased the Km of L-leucine uptake without affecting Vmax, indicating altered carrier affinity.
• L-leucine uptake led to intravesicular acidification, which was enhanced by countertransport and inward proton gradients.
• Leucine-dependent cytoplasmic acidification was prolonged by choline or amiloride, and amiloride inhibited leucine uptake in a Na+-dependent manner.

Conclusions:

• Chang liver cells possess an amino acid-H+ cotransport system in their plasma membrane.
• This system is coupled to an amiloride-sensitive Na+/H+ exchange system, suggesting a coordinated regulation of amino acid and ion transport.