A note on the cellular effects of nystatin in single myoballs

Volume changes in single L6 myoblasts (myoballs) exposed to nystatin solutions were followed on single cell level by means of quantitative video image analysis. The myoblasts swelled in nystatin solutions. The volume change was dependent on the nystatin concentration, the threshold concentration being 12.5 mumol/l of nystatin freshly dissolved in Krebs solution. The threshold effect was triphasic: a slight initial volume decrease (shrinkage) for about 2 min followed by a volume increase and, after about 10 min by a significant volume decrease. At twice as high nystatin concentration (25 mumol/l) the final shrinkage phase was lacking. At 50 mumol/l concentration the volume increased continually after a delay of about 1-2 min. and reached a plateau of about 350% of the original volume. At 100 mumol/l concentration of nystatin the myoblasts increased their volume in about five min to more than 500% of the original value. The effects of nystatin diminished upon prolonged storage of nystatin Krebs solution. Nystatin solutions (50 mumol/l) prepared 3 hours before use were stil active to about 80%. Volume changes in 100 mumol/l nystatin solutions were, however, substantially diminished (to about 20%) 5 hours after the preparation of the nystatin solution. By replacing external Na+ by TEA+ in the presence of external Cl- a regulatory volume decrease was observed to subnormal values; the myoblast volume shrank to about half of the control value. The volume changes were reversible after reintroduction of Krebs solution. The regulatory volume decrease to subnormal values was also observed after replacing external Cl- by glutamate anion in the presence of external Na. The volume changes were, however, not reversible after reintroduction of Krebs solution. The swelling of myoblasts in 50 mumol/l nystatin Krebs solution continued after a definite enlargement of the whole myoblast was reached with the formation of several blebs, which eventually coalesced to form a continuous layer around the myoballs. The enlarged vesicles in nystatin solutions were able to start and fulfill the mitotic cycle. Cell volume measurements represent a handy means for checking the activity of nystatin solutions for the perforated patch experiments.