CHANGES IN THE ACTIVITIES OF VOLUME-REGULATORY ION CHANNELS DURING CELL DIFFERENTIATION OF MOUSE B LYMPHOCYTES.

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A variety of cell species, including T lymphocytes, can readjust their volume in a hypotonic medium after the initial osmotic swelling due to KC1 effluxes. However, no regulatory volume decrease (RVD) has been found in mature human B lymphocytes (Grinstein, 1983). Supporting this observation, we found that a mature murine B cell line (DW 101) has little ability of the volume regulation under hypotonic conditions. In addition, mouse pre-B cell lines (DW 34, DW 8 and an abelson leukemia virustransformed pre-B cell line) were also found to exhibit no RVD within several tens ofminutes. In contrast, pre-pre-B cell lines (SCID 7, abelson virus-transformed pre-pre-B) could show rapid volume regulation upon hypotonic stress. The RVD was suppressed by elevating the extracellular K^+ concentration and facilitated by reducing the extracellular C1^- channel blocker (SITS) inhibited the RVD of pre-pre-B cells. When a cationic ionophore (gramicidine) was added, the RVD was observed i n hypotonically swollen pre-B cells under the low-Na^+ condition. Thus, it is suggested that the RVD mechanism (presumably K^+ transporters) becomes impaired during the mouse B-lineage cell differentiation at the pre-B stage. In fact, whole-cell recordings with patch electrodes showed that both K^+ and C1^- currents became activated in an Abelson pre-pre-B cell line upon a hypotonic challenge, but that only the latter channel was activated in the pre-B cell line after hypotonic stress.