Uptake and metabolism of L-alanine by freshly isolated trout hepatocytes has been analyzed. This amino acid is incorporated ‘uphill’ by different carriers, either Na+-dependent or Na+-independent. Na+-dependent uptake shows the characteristics of an ASC system on the basis of cation dependence and substrate preferences. The Na+-independent uptake is split between an L-cysteine-sensitive system and a non-saturable component. No uptake through system A has been found, suggesting that this carrier is lacking in trout hepatocytes. On the basis of inhibition by several preferred amino acids, L-alanine is not taken up through either the L or N systems.
Fasting induced changes in both the uptake of L-alanine and its metabolism to CO2 and glucose. There was an increase in uptake that showed an inverse relationship with L-alanine plasma levels. Glucose production from L-alanine rose during food deprivation, while CO2 production showed an initial increase, similar to that of glucose. At the end of the fasting time considered, however, there was a drop in CO2 production, indicating a different kind of regulation for alanine oxidation and gluconeogenesis.
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