Transport of L-methionine in rat intestine and kidney.

Abstract

Extract: L-Methionine transport was studied in vitro in rat kidney cortex slices and intestinal segments. In both tissues L-(C14) methionine at concentrations of 0.065 mmol was accumulated against a chemical concentration gradient by processes which obeyed saturation kinetics. In both tissues anaerobic conditions (incubation in 95% N2 and 5% O2 atmosphere) inhibited methionine accumulation (P < 0.001 and P < 0.025, respectively). The processes were sodium dependent. Addition of 0.3 Msucrose produced significant (P < 0.001) inhibition of L-methionine accumulation in the kidney. L-Methionine transport was essentially pH independent. A series of amino acids, including representatives of the neutral, dibasic and imino acid groups at 2.4 DIM concentrations, failed to inhibit methionine transport with the exception that valine proved a potent inhibitor of transport in the intestine (P < 0.01) and ethionine in the kidney (P < 0.025). Methionine inhibited glycine accumulation in the kidney (P < 0.025) and intestine (P < 0.001), but failed to affect lysine transport in either tissue. Speculation: The data presented indicate that methionine uptake in the gut and the kidney has the characteristics of an active transport process which is unaffected by most other amino acids. These findings suggest that methionine is either transported by an independent mechanism and/or by a transport system which is shared with the other neutral amino acids but for which it has a much higher affinity.