Free calcium and calpain I activity.

Activation of purified calpain I proceeds through a Ca(2+)-induced autolysis from the 80 kDa catalytic subunit to a 76 kDa form via an intermediate 78 kDa form, and from a 30 kDa form to a 18 kDa form as the result of two autocatalytic processes (intra and intermolecular). The minimum Ca2+ requirements for autolysis and proteolysis have been determined by physico-chemical and electrophoretic methods in the presence or absence of a digestible substrate. According to our results the activation process needs less free Ca2+ than the proteolysis of a digestible substrate, which means that proteolysis is really subsequent to activation.

[Is muscular acetylcholinesterase activity correlated with the intracellular concentration of free calcium?].

The role of the calcium ion Ca2+ as an agent of intracellular control in a variety of physiological processes is well established. In vertebrate skeletal muscle fibers, Ca2+ is involved in muscle contraction, modulation of membrane permeability and regulation of metabolic activity. Recently it was suggested that ion fluxes through membranes regulate the level of two cholinergic macromolecules, the acetylcholine receptor and the A12 form of acetylcholinesterase (AChE), the presumed synaptic form of the enzyme.

Movements of fluorescent probes in the mechanism of cell fusion induced by poly(ethylene glycol).

It has been claimed that purified poly(ethylene glycol) (PEG) is able only to aggregate cells and not to fuse them. In our hands, purified PEG 6000 (recrystallized/dialysed) induces both aggregation and fusion of human erythrocytes, and the mechanism of fusion by the purified polymer has been investigated with fluorescent probes. No movement of a carbocyanine probe or of octadecyl rhodamine B chloride from labelled to unlabelled cells occurred in the absence of PEG or with cells treated with concanavalin A, protamine or spermine.

Transport of mercury compounds across bimolecular lipid membranes: effect of lipid composition, pH and chloride concentration.

The use of bimolecular lipid membranes (BLM) as model membrane allows the analysis of the transport of mercury compounds across the lipidic barriers of biological membranes. The results of flux measurements show that two mercury compounds--HgCl2 and CH3HgCl--cross the BLM but the overall permeabilities are dependent on the pH of the aqueous media, and are not apparently influenced by the different phospholipid constituents of the bilayers. On the other hand, electrical measurements show that, function of the chemical speciation, the transport of this metal is done essentially in the neutral form.

Modifications of membrane cholesterol content affects electrical properties and prolactin release of cultured pituitary cells.

Treatment of cloned pituitary cells (GH3/B6) with cholesterol-enriched liposomes, which presumably increases membrane cholesterol content, affects the passive and active electrophysiological properties and stimulates the release of prolactin (PRL).