C1 Fluxes in L6 Myoblasts

Efflux of 3 G C1 ions was followed in undifferentiated L6 myoblasts at rest and after exposure to hypotonic saline in order to test participation of the chloride exit in regulatory volume decrease mechanism. The efflux curve can be fitted at least with two t ime constants. After the hypotonic stress the slow rate constant increases almost threefold, from 0.021 ±0.019 m i n 1 normal saline to 0.060 ±0.019 m i n " 1 in hypotonic solution. K e y words: Isotopic fluxes — Chloride efflux — Muscle cell line — L6 myoblasts — Osmotic cell swelling — Hyposmotic stress — Regulatory volume decrease — Cell volume regulation We have demonstrated recently (Zachar and Hurňák 1995) the existence of re­ gulatory volume decrease in L6 myoblasts, first discovered in blood cells (Kregenow 1981) and since t h e n observed in a number of different cells (for a recent review see e.g. Hoffmann and Simonsen 1989; Hoffmami 1992; Lang et al. 1993). Most probably t h e volume recovery is due to the exit of K + and C I ions by concomitant loss of water, as follows from the effect of substitution of K and CI ions on the volume recovery in these cells. The mechanism of exit of K + and Cl~ remains to be elucidated. There are in general at least three possibilities how this may occur: 1) via separate K + and Cl~ channels, 2) by means of neutral K-Cl cotransport, and 3) by parallel operation of cation and anion exchange mechanisms (Hoffmann and Simonsen 1989). We are reporting here on experiments with labeled 3 ( i Cl fluxes which were aimed to test the participation of chloride exit in regulatory volume decrease mecha­ nism in undifferentiated L6 myoblasts. We have demonstrated that the 3 C C1 efflux curve can be fitted at least with two rate constants. After the hypotonic stress the slow rate constant increases almost threefold. The L6 cells were obtained from American Type Culture Collection (A.T.C.C.;