Hepatic basolateral plasma high-affinity Ca2+-ATPase is inhibited by nitric oxide and peroxynitrite anion

The aim of the present work was to study the effect of nitric oxide (NO) an d peroxynitrite radicals on basolateral liver plasma membrane activity of h igh-affinity Ca2+-ATPase. Basolateral membranes were isolated by ultracentr ifugation in sucrose gradients and characterized enzymatically. Basolateral membranes were incubated with S-nitroso-N-acetyl-penicillamine (SNAP, an N O donor) or 3-morpholinosydnonimine (SIN-1, a peroxynitrite donor). The lib eration of NO or peroxynitrite was monitored by measuring NO2-+NO3- in the medium. Calcium ATPase activity decreased by NO and peroxynitrite in a conc entratian-dependent manner. It is likely that both compounds inhibit ATPase activity by oxidation of thiol groups of the enzyme. Our results suggest t hat NO may exert part of its cytotoxic properties by inhibiting the calcium ATPase activity. Inhibition of calcium ATPase may result in Ca2+ accumulat ion, which in turn may be useful as an intracellular signal. Copyright (C) 2000 John Wiley & Sons, Ltd.