Possible Involvement of Nitric Oxide in Acetylcholine-Induced Increase of Intracellular Ca^2+ Concentration and Catecholamine Release in Bovine Adrenal Chromaffin Cells

The role of nitric oxide (NO) in neurotransmitter release was studied using bovine adrenal medullary chromaffin cells. L-Arginine and sodium nitroprusside (SNP) slightly increased the intracellular free calcium concentration ([Ca^2+]_i ), and the effects of the agents were dependent on the presence of the extracellular Ca^2+ ([Ca^2+ ]_o ), but were not blocked by verapamil (30 μM) or diltiazem (30 μM). SNP enhanced the acetylcholine (ACh)-induced rise in [Ca^2+ ]_i in the presence but not in the absence of [Ca^2+ ]_o . The effects of L-arginine but not those of SNP were inhibited by N^ω -nitro-L-arginine (L-NNA). L-NNA significantly reduced the ACh-induced rise in [Ca^2+ ]_i and catecholamine (CA) release, and the reduction was restored by L-arginine but not by D-arginine. These results suggest a possible involvement of NO in ACh-induced [Ca^2+ ]_i rise and CA release in bovine adrenal chromaffin cells.