Diabetes and insulin-induced stimulation of L-arginine transport and nitric oxide synthesis in rabbit isolated gastric glands

1. The properties of L-arginine transport have been characterized and correlated with cGMP production (index of nitric oxide (NO)) in whole gastric glands isolated from non-diabetic and alloxan-diabetic rabbits. 2. In non-diabetic and diabetic glands, transport of L-arginine was stereoselective, Na+ and pH independent and inhibited by other cationic amino acids. L-Arginine transport was slightly inhibited by L-leucine and L-phenylalanine, but unaffected by other neutral amino acids. 3. Diabetes enhanced the V-max for saturable L-arginine transport from 10.7 +/- 1.0 to 17.7 +/- 0.5 pmol (mg protein)(-1) s(-1), with negligible changes in K-m. 4. Accumulation of the membrane potential-sensitive probe tetra [H-3]phenylphosphonium (TPP+) was increased 2-fold in diabetic compared with non-diabetic gastric glands, suggesting a membrane hyperpolarization. 5. Basal intracellular cGil'lP levels were elevated 2-fold in diabetic gastric glands, and in non diabetic glands histamine, vasoactive intestinal peptide, and bradykinin increased cGMP levels. The NO sy-nthase inhibitor N-G-nitro-L-arginine methyl ester (100 mu M) abolished basal cGMIP accumulation. 6. Addition of extracellular L-arginine induced a concentration-dependent increase in cGMP levels in gastric glands isolated from non-diabetic rabbits, but had no effect on elevated cGMP levels in diabetic glands. 7. Insulin induced a rapid (5 min) concentration-dependent increase in cGMP levels in nondiabetic gastric glands, but reduced eles ated cGMP levels in diabetic gastric glands. 8. The present study has identified a specific transport system for L-arginine in gastric glands svhich resembles the classical system y(+). Our findings also pros ide the first direct evidence that diabetes increases the basal activity of system y(+) and NO synthase in gastric glands. The differential modulation of L-arginine transport by insulin and L-arginine identified in non-diabetic and diabetic glands, may be of importance in protecting the gastric mucosa from injuries associated with diabetes.