cAMP regulates nitric oxide production and ouabain sensitive Na+, K+-ATPase activity in SH-SY5Y human neuroblastoma cells

We investigated the relation between cyclic AMP (cAMP) and nitric oxide (NO ) production, as well as the effect of NO on Na+, K+-ATPase activity in the human neuroblastoma cell line SH-SY5Y. Two cAMP agonists, dibutyryl cAMP ( DBC) and beraprost sodium (BPS), increased cAMP accumulation and NO product ion in a time and dose dependent manner at 50 mmol/l glucose. On the other hand, cellular sorbitol and myo-inositol contents and protein kinase C acti vity were not altered by DBC or BPS. A specific protein kinase A inhibitor, H-89, suppressed increases in nitrite/nitrate and cyclic GMP (cGMP) and pr otein kinase A activity stimulated by DBC or BPS. This finding suggests tha t cAMP stimulates NO production by activating protein kinase A via a pathwa y different from the sorbitol-myo-inositol-protein kinase C pathway. We obs erved that an NO donor, sodium nitroprusside, and an NO agonist, L-arginine , enhanced ouabain sensitive Na+, K+-ATPase activity at 50 mmol/l glucose. We also found that a nitric oxide synthase inhibitor, N-G-nitro-1-arginine methyl ester (L-NAME), inhibited Na+, K+-ATPase activity at 5 mmol/l glucos e, and partially suppressed the enzyme activity stimulated by DBC or BPS. T he results of this study suggest that cAMP regulates protein kinase A activ ity, NO production and ouabain sensitive Na+, K+-ATPase activity in a casca de fashion. The results also suggest that protein kinase A at least partial ly regulates Na+, K(+-)ATPase activity without mediation by NO in SH-SY5Y c ells. We speculate that cAMP and NO are two important regulatory factors in the pathogenesis of diabetic neuropathy.