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Evidence shows that Na(+)/K(+)-ATPase from kidney, brain and liver is inhibited by nitric oxide (NO) and peroxynitrite anion (ONO(2) (-)), but the mechanism is unknown. The aim of the present work was to study the inhibitory effect of NO and ONO(2) (-) on erythrocyte Na(+)/K(+)-ATPase. Erythrocyte membranes were isolated from male Wistar rats by hypotonic washing. The membranes (free from haemoglobin) were incubated for Na(+)/K(+)-ATPase activity measurement at various concentrations of ATP in the presence or absence of 400 microM SNAP (an NO donor) or 100 microM SIN-1 (an ONO(2)(-) donor). At these concentrations, SNAP and SIN-1 released about the same amount (100 microM) of NO or ONO(2)(-), respectively, as monitored by measuring NO(2)(-) + NO(3)(-). Both SNAP and SIN-1 decreased V(max) by ca. 75% but they did not decrease the apparent affinity of the Na(+)/K(+)-ATPase for the substrate (a decrease of K(m) was even observed after SNAP treatment). The pattern of this inhibition is compatible either with oxidation of SH groups directly involved in ATP binding but in a way that is not surmountable by increasing the substrate concentration ("non-competitive") or with oxidation of SH groups located outside the active site of the enzyme but important for the activity of the enzyme.

Pleistophora finisterrensis n. sp. is a microsporidian parasite of the hypoaxial musculature of the blue whiting Micromesistiuspoutassou (Risso). Foci of infection are between 3 and 6 mm in length and have no evident effects on adjacent muscle fibres. We found only a single type of spore (uninucleate, with mean dimensions of 4 x 2 #m in fresh preparations), contained within sporophorous vesicles (mean diameter 19 #m in fresh preparations; 150-250 spores per vesicle). All of the development stages of this microsporidian are monokaryotic. The meronts are initially uninucleate and bounded by a plasmalemma. Towards the end of merogony, meronts are multinucleate plasmodia with a well-defined surface coat. Sporogony is polysporous, with multinucleate sporonts, which likewise have a well-defined surface coat (about 130 nm thick), dividing by plasmotomy to give rise to uninucleate sporoblasts. The polar tube is isofilar and consists of 8-9 turns in the posterior half of spore. The polaroplast is made up of an anterior lamellar part and a posterior vesicular part.

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