INSULIN STIMULATES CATIONIC AMINO-ACID-TRANSPORT ACTIVITY IN THE ISOLATED-PERFUSED RAT PANCREAS

The effects of exogenous insulin, glucagon and streptozotocin-diabetes on influx (15 s) of L-lysine via a cationic amino acid transporter re sembling system yi were investigated in the isolated perfused rat panc reas. In non-diabetic pancreata, transport of L-lysine was saturable w ith an apparent K-m of 2 . 11 +/- 0 . 29 mM and V-max of 2 . 21 +/- 0 . 20 mu mol min(-1) g(-1) (n = 6). Bovine insulin (100 mu u ml(-1)) in creased the maximal transport rate (V-max = 3 . 49 +/- 0 . 30 mu mol m in(-1) g(-1), n = 4, P < 0 . 05) for L-lysine 1 . 6-fold without alter ing the K-m. L-Lysine transport was not elevated significantly in diab etic pancreata, although insulin (100 mu u ml(-1)) enhanced transport to values measured in non-diabetic preparations. Human glucagon (1 . 5 x 10(-9) M) had no stimulatory effect on L-lysine transport. These fi ndings provide the first evidence that exogenous insulin stimulates ca tionic amino acid transport activity in the exocrine pancreatic epithe lium. Activation of the cationic pancreatic amino acid transporter may provide a mechanism to enhance the supply of L-arginine and thus sust ain nitric oxide-mediated pancreatic secretion in response to islet ho rmones and secretagogues.