Amino acid transport in the rat exocrine pancreas. I. Transport of neutral amino acids and their utilization in protein synthesis.

The transport and utilization of three neutral amino acids in protein synthesis was studied using isolated pancreatic lobules in vitro. The significance of the extracellular and intracellular amino acid pool in this process was analyzed removing the extracellular pool (labeled by inulin) by a cold-wash procedure. This was especially useful in short-term experiments. Double-labeling experiments indicated a predominant utilization of the intracellular amino acid pool during protein synthesis. The advantage of isolated pancreatic lobule preparations compared to tissue fragments or slices was emphasized by fine structural studies. Using freeze-etching techniques on the same preparations, differences in the distribution of membrane particles between luminal and lateral plasma membranes described earlier were confirmed, as well as the abundant occurrence of gap junctions on both membrane faces.