HYPOTONICITY AND THROMBIN ACTIVATE TAURINE EFFLUX IN BC(3)H1 AND C2C12 MYOBLASTS THAT IS DOWN-REGULATED DURING DIFFERENTIATION

The efflux of organic osmolytes such as taurine is an important mechan ism by which cells regulate their volume. The effects of hypotonicity and thrombin on taurine efflux were studied in BC(3)H1 and C2C12 cells , two mouse myoblastic cell lines that can be induced to differentiate with serum deprivation. In proliferating cultures of both cell types preloaded with [H-3]taurine, exposure to 27% hypotonicity activated a 10- to 20-fold increase in [H-3]taurine efflux (J(tau)). This effect w as blocked by the Cl- channel inhibitors NPPB and flufenamic acid. Thr ombin and the thrombin receptor agonist SFLLRN also activated J(tau) t hat was abolished by NPPB and flufenamic acid. Together, hypotonicity and thrombin synergistically activated J(tau). In differentiated myocy tes, the effect of thrombin was abolished, while that of hypotonicity was significantly reduced. These results suggest that (i) hypotonicity and thrombin activate taurine-permeable anion channels in BC(3)H1 and C2C12 cells, and (ii) these anion channels may be involved in cell pr oliferation. (C) 1997 Academic Press.