PROTECTION OF NITRERGIC NEUROTRANSMISSION BY AND COLOCALIZATION OF NEURAL NITRIC-OXIDE SYNTHASE WITH COPPER-ZINC SUPEROXIDE-DISMUTASE

This study examined in the rat anococcygeus muscle the tissue distribu tion of copper zinc superoxide dismutase, the activity of CuZn SOD, an d the role of CuZn SOD in protecting nitric oxide from destruction by superoxide anion. Immunohistochemical studies revealed intense stainin g for CuZn SOD in neuronal nitric oxide synthase-containing nerves. Mu scle strips contained 1081 +/- 300 units SOD g(-1) wet tissue (mean +/ - S.E.M., n = 5). Diethyldithiocarbamate (2 mM) inhibited CuZn SOD act ivity in superatant fractions of muscle homogenates by 34% (P < 0.01 n = 5), an effect reversed by CuCl2, (2 mM). In control conditions, ele ctrical field stimulation of nitrergic inhibitory nerves evoked a 61.5 +/- 10.5% (n = 10) relaxation against guanethidine (30 mu M)-induced tone. Relaxation evoked by nitrergic inhibitory nerves was neither pot entiated by exogenous CuZn SOD (10-1000 U ml(-1)) nor by the O(2)(-)ge nerator pyrogallol (30 mu M). When diethyldithiocarbamate (2 mM) was p resent, stimulation of nitrergic inhibitory nerves evoked a 51.7 +/- 1 0.8% (P < 0.05, n = 10) relaxation against guanethidine (30 mu M)-indu ced tone. Addition of pyrogallol (30 mu M) to diethyldithiocarbamate-t reated (2 mM for 30 min) muscle strips further reduced nerve-evoked re laxation to 30.7 +/- 7.6% (P< 0.01, n = 10). The inhibitory effect of pyrogallol was reversed by exogenous CuZn SOD (200 U ml(-1)). Diethyld ithiocarbamate (? mM) hail no effect on relaxation evoked by exogenous NO(1 mu M). The data indicate that CuZn SOD is present in rat anococc ygeus muscle, that it is colocalized with nNOS in the nitregic nerves, and that it protects NO from destruction by O-2(-).