Production of nitric oxide by mussel (Mytilus galloprovincialis) hemocytes and effect of exogenous nitric oxide on phagocytic functions

In the present study, the ability of mussel (Mytilus galloprovincialis) hemocytes to produce nitric oxide (NO) in response to phorbol myristate acetate (PMA) was determined using the Griess reaction. Significant NO production was found in these cells in response to PMA. This stimulation was reversed in the presence of the NO synthase inhibitor, N-G-methyl-L-arginine (L-NMMA). Moreover, the effect of the pre-incubation of hemocytes with NO was also determined on phagocytic immune functions of mussel hemocytes using two NO donors, glycerin trinitrate (GTN) and S-nitroso-N-acetyl-penicillamine (SNAP). In the case of GTN, a visible cytotoxic effect of the compound at the higher doses was observed. Those GTN concentrations that did not have a negative effect on hemocyte viability did not produce sufficient NO to significantly alter the chemiluminescent response to zymosan in all cases, nor the ability of hemocytes to phagocytose bacteria (Escherichia coli). SNAP, however, did not affect cell viability at either of the concentrations used and produced NO levels up to 13-fold higher than controls after 2 h of incubation. In this case, NO exogenously produced by SNAP significantly inhibited the chemiluminescent response of mussel hemocytes, whereas it did not have a significant effect on the capability of these cells to phagocytose bacteria. (C) 2002 Elsevier Science Inc. All rights reserved.