FUNCTIONAL COUPLING OF NITRIC-OXIDE SYNTHASE AND SOLUBLE GUANYLYL CYCLASE IN CONTROLLING CATECHOLAMINE SECRETION FROM BOVINE CHROMAFFIN CELLS

This study was designed to evaluate whether the enzymes of the nitric oxide/cyclic-GMP pathway, nitric oxide synthase and soluble guanylyl c yclase, are functionally coupled in controlling catecholamine secretio n in primary cultures of bovine chromaffin cells. In immunocytochemica l studies, 80-85% of the tyrosine hydroxylase-positive chromaffin cell s also possessed phenylethanolamine-N-methyltransferase, indicating th eir capability to synthesize epinephrine. Immunoreactivity for neurona l-type nitric oxide synthase was found in over 90% of all chromaffin c ells. Reverse transcription-polymerase chain reaction also demonstrate d neuronal-type nitric oxide synthase messenger RNA. Immunoreactivity for soluble guanylyl cyclase was detectable in over 95% of chromaffin cells. Double-labeling immunofluorescence studies co-localized neurona l-type nitric oxide synthase and soluble guanylyl cyclase with tyrosin e hydroxylase and phenylethanolamine-M-methyltransferase in the majori ty of chromaffin cells. Chromaffin cells possessed basal nitric oxide synthase activity which could be stimulated by acetylcholine and inhib ited by N-G-nitro-L-arginine methyl ester. Activation of soluble guany lyl cyclase by endogenously synthesized nitric oxide or the nitric oxi de donor compound sodium nitroprusside was blocked by the inhibitor of soluble guanylyl cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. Catecholamine release and the increase in cytosolic Ca2+ concentratio n evoked by acetylcholine were enhanced by inhibitors of the endogenou s nitric oxide/cyclic-GMP pathway such as N-G-nitro-L-arginine methyl ester, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one and the protein kin ase G inhibitor Rp-8-pCPT-cGMPS. These data indicate that chromaffin c ells possess an autocrine nitric oxide/cyclic-GMP pathway tonically co ntrolling the inhibition of catecholamine release. (C) 1997 IBRO. Publ ished by Elsevier Science Ltd.