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) and peroxynitrite radicals on basolateral liver plasma membrane activity of high-affinity Ca2+-ATPase. Basolateral membranes were isolated by ultracentrifugation in sucrose gradients and characterized enzymatically. Basolateral membranes were incubated with S-nitroso-N-acetyl-penicillamine (SNAP, an NO donor) or 3-morpholinosydnonimine (SIN-1, a peroxynitrite donor). The liberation of NO or peroxynitrite was monitored by measuring in the medium. Calcium ATPase activity decreased by NO and peroxynitrite in a concentration-dependent manner. It is likely that both compounds inhibit ATPase activity by oxidation of thiol groups of the enzyme. Our results suggest that NO may exert part of its cytotoxic properties by inhibiting the calcium ATPase activity. Inhibition of calcium ATPase may result in Ca2+ accumulation, which in turn may be useful as an intracellular signal.