A NOTE ON THE CELLULAR EFFECTS OF NYSTATIN IN SINGLE MYOBALLS

Volume changes in single L6 myoblasts (myoballs) exposed to nystatin s olutions were followed on single cell level by means of quantitative v ideo image analysis. The myoblasts swelled in nystatin solutions. The volume change Miss dependent on the nystatin concentration, the thresh old concentration being 12.5 mu mol/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 incre ase and, after about 10 min by a significant volume decrease. At twice as high nystatin concentration (25 mu mol/l) the final shrinkage phas e was lacking. At 50 mu mol/l concentration tile volume increased cont inually after a delay of about 1-2 min. and reached a plateau of about 350% of the original volume. At 100 mu mol/l concentration of nystati n the myoblasts increased their volume in about five mill to more than 500% of the original value. The effects of nystatin diminished upon p rolonged storage of nystatin Krebs solution. Nystatin solutions (50 mu mol/l) prepared 3 hours before use were stil active to about 80%. Vol ume changes in 100 mu mol/l nystatin solutions were, however, substant ially diminished (to about 20%) 5 hours after the preparation of the n ystatin 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 sol ution. The regulatory volume decrease to subnormal values was also obs erved 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. Tile swelling of myoblasts in 50 mu mol/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 myob alls. The enlarged vesicles in nystatin solutions were able to start a nd fulfill the mitotic cycle. Cell volume measurements represent a han dy means for checking the activity of nystatin solutions for the perfo rated patch experiments.