MOJAVE TOXIN AFFECTS FUSION OF MYOBLASTS AND VIABILITY OF MYOTUBES IN CELL-CULTURES

Mojave toxin is a neurotoxic, heterodimeric phospholipase isolated from the venom of Crotalus scutulatus scutulatus. Responses, of primary rat muscle cell cultures and clonal muscle cell lines to treatment with Mojave toxin and its constituent subunits were examined. Continuous exposure of cells to 0.5-mu-M or 1.0-mu-M Mojave toxin or the basic subunit, added 24 hr after plating, prevented fusion of primary myoblasts and C2 myoblasts to multinucleate myotubes. Under the same experimental conditions, some myotube formation was observed when RMo cells were used, but the number and size of the myotubes were reduced substantially compared to untreated controls. The addition of Mojave toxin to established myotubes that arose from differentiation of primary myoblasts or C2 myoblasts essentially led to total disappearance of the myotubes from the cell layer within 48 hr. Myotubes from RMo cells treated in the same manner, however, did not disappear, but they were smaller and less numerous than comparable controls. Similar results were generated by exposure of myotubes to the basic subunit of Mojave toxin under the same conditions. The underlying layer of mononucleate cells was retained in both instances. Toxin-free cultures continued to develop in the usual manner. Treatment with 1.0-mu-M concentrations of the acidic subunit, pancreatic phospholipase A2 or a non-neurotoxic phospholipase from Naja naja atra gave results indistinguishable from untreated control cultures.