Inhibition of myoblast fusion by lysosomotropic amines

Fusion of cultured chick embryo myoblasts was inhibited by treatment with several lysosomotropic amines. The concentrations required for half-maximal inhibition of fusion were approximately 2 μM for chloroquine, 30 μM for tributylamine, 3.2 mM for ammonium chloride, and 3.3 mM for methylamine. All the amines inhibited fusion appreciably at concentrations lower than those that reduced cell density. Both the rate and extent of fusion were affected by the amines, which had to be present for about 20 hr before the usual onset of fusion. Inhibition of fusion was reversible by transfer of inhibited cells to fresh medium. The amines did not cause accumulation of a nondialyzable inhibitor in the culture medium. Levels of creatine kinase increased by eight-fold or more between 18 and 65 hr in cultures treated with tributylamine or chloroquine, although this increase was not as pronounced as in control cultures. The increased creatine kinase activity in amine-treated cultures was due mainly to the BB and MB isozymes, with relatively little increase in the MM isozyme.