MODULATION OF BASAL NITRIC OXIDE-DEPENDENT CYCLIC-GMP PRODUCTION BY AMBIENT GLUCOSE, MYOINOSITOL, AND PROTEIN-KINASE-C IN SH-SY5Y HUMAN NEUROBLASTOMA-CELLS

Defective tissue perfusion and nitric oxide production and altered myo -inositol metabolism and protein kinase C activation have been invoked in the pathogenesis of diabetic complications including neuropathy. T he precise cellular compartmentalization and mechanistic interrelation ships of these abnormalities remain obscure, and nitric oxide possesse s both neurotransmitter and vasodilator activity. Therefore the effect s of ambient glucose and myo-inositol on nitric oxide-dependent cGMP p roduction and protein kinase C activity were studied in SH-SY5Y human neuroblastoma cells, a cell culture model for peripheral cholinergic n eurons. D-Glucose lowered cellular myo-inositol content, phosphatidyli nositol synthesis, and phosphorylation of an endogenous protein kinase C substrate, and specifically reduced nitric oxide-dependent cGMP pro duction a time- and dose-dependent manner with an apparent IC50 of sim ilar to 30 mM. The near maximal decrease in cGMP induced by 50 mM D-gl ucose was corrected by the addition of protein kinase C agonists or 50 0 mu M myo-inositol to the culture medium, and was reproduced by prote in kinase C inhibition or downregulation, or by myo-inositol deficient medium. Sodium nitroprusside increased cGMP in a dose-dependent fashi on, with low concentrations (1 mu M) counteracting the effects of 50 m M D-glucose or protein kinase C inhibition. The demonstration that ele vated D-glucose diminishes basal nitric oxide-dependent cGMP productio n by myo-inositol depletion and protein kinase C inhibition in periphe ral cholinergic neurons provides a potential metabolic basis for impai red nitric oxide production, nerve blood flow, and nerve impulse condu ction in diabetes.