Daily Rhythmic Changes in Amino Acid Transport in Isolated Intestinal Epithelial Cells from Rats on Restricted-feeding Regimen

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Circadian rhythmicity was investigated in isolated small intestine and mucosal epithelial cells from rats on restricted-feeding regimen (food available from 17 : 00 to 23 : 00 every day). In the isolated intestine, daily rhythms synchronized to meal-timing were found in the activity patterns of L-leucine, L-lysine and D-glucose transport, and mucosal γ-glutamyltransferase and sucrase, and in the rates of lactate formation from glucose; the nadirs occurred at 12 : 00 and the peaks at 23 : 00. These same patterns were also noted with the mucosal epithelial cells prepared at distinct times of day from rats on meal-feeding regimen. The fasted rat intestine responded to refeeding with prompt increase in transport activity, i.e., out of phase with the original rhythm. Intraperitoneal administration of cyloheximide suppressed the daily rise in leucine transport activity, indicating that the transport rhythm was entrained by or closely associated with the rhythmic fluctuation in protein synthesis in the epithelial cells, which in turns is cued by the feeding schedule. The kinetic parameters estimated for leucine transport, the apparent affinity constant for transport and the maximal transport rate, were significantly higher at high activity periods. It is suggested that the rhythmic increase in transport activity is not only associated with membrane hyperpolarization but may be mediated by the emergence of a high capacity transport system.
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Daily Rhythmic Changes in Amino Acid Transport in Isolated Intestinal Epithelial Cells from Rats on Restricted-feeding Regimen

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