REGULATORY VOLUME DECREASE IN CULTURED MYOBLASTS L6

A method is described for measuring volume changes in single L6 myobla sts at a stage of proliferating ''myoballs'', which allows to follow v olume changes on single cell level by means of quantitative video imag e analysis. Myoblasts exposed to hypoosmotic or hyperosmotic challenge s for up to 3-5 min behave as osmometers. The relative cell volume is a linear function of the reciprocal of the relative osmolality in the range 0.5-2T. Cells exposed to hypotonic Krebs solution with Na+ and C l- ions as the main ions exhibit volume readjustment towards the origi nal level. The regulatory volume decrease (RVD) was complete after abo ut 15 min in hypotonic solution with C-max (maximum RVD) increasing wi th the decrease in osmolality in the test solution. By replacing exter nal Na+ by K+ in the presence of external Cl- regulatory volume decrea se was reversed; myoblast volume continued to increase. RVD was presen t after replacing Cl- with NO3. Quinine (0.5 mmol/l) partially blocked RVD. It is suggested that RVD in L6 myoblasts is mediated mainly by s eparate K+ and Cl- channels.