[Is muscular acetylcholinesterase activity correlated with the intracellular concentration of free calcium?]. / L'activité de l'acétylcholinestérase musculaire est-elle corrélée à la concentration du Ca2+ intracellulaire libre?

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. Muscle cells paralysed by veratridine, which maintains the Na+ channel in the open state, showed an increase in total AChE and in the levels of the A12 form. The effect of veratridine on AChE was blocked in the presence of agents that block Ca2+ permeability suggesting that Ca2+ is involved in this effect. To understand whether the level of muscle AChE is related in some way to the level of free intracellular Ca2+, we analysed the variations of Ca2+ levels in rat muscle cells treated by agents which modify the ionic permeabilities. This level was determined by spectrofluorimetry using the fluorescent Ca2+ indicator: Quin 2. However no correlation between these parameters was observed in our experimental conditions.

Incorporation of killer functions from murine T-cytotoxic spleen cultures in somatic hybrids.

Fusions between the BW5147 thymoma and spleen cells with specific T-cytotoxic activity led to the recovery of a remarkably high percentage of non-specific, strictly lectin-dependent killer hybrids (70 to 95% of all hybrids tested, depending upon the particular fusion experiment). After one or several recloning steps, these hybrids behaved as very stable killers, growing in regular, interleukin-2-free growth medium, with some of them maintaining their lytic characteristics for over one year. Among these lectin-dependent killers, only two exhibited target specificity, but both lost this property within the first month after fusion. These results are discussed in light of other rare reports concerning incorporation of cytotoxic T-lymphocyte-specific functions in somatic hybrids.