Volume response of quiescent and interleukin 2-stimulated T-lymphocytes to hypotonicity

Regulatory volume decrease (RVD) in lymphocytes in response to hyptonically induced swelling is dependent on the membrane permeabilities of K⁺, Cl^-, and H₂O. We used electronic cell sizing, cell water determination, and the whole cell patch-clamp method to study these membrane permeabilities in the cloned mouse T-lymphocyte, L2. Quiescent L2 cells expressed low levels of a voltage-gated K⁺ channel and show no RVD at 25°C. In contrast, L2 cells stimulated to proliferate with the growth factor interleukin 2 have increased K⁺ conductance and show RVD in response to hypotonicity. RVD in stimulated cells is blocked by quinine and verapamil at levels that also completely block the voltage-gated K⁺ conductance. Swollen, unstimulated L2 cells can be induced to shrink by addition of the monovalent cation ionophore gramicidin in the presence of impermeant extracellular organic cations; gramicidin also enhances the rate of RVD in stimulated cells. Additionally, the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) blocks this gramicidin-facilitated RVD. These results suggest that a minimum requisite Cl^- permeability is present even in the unstimulated L2 cells, that a necessary and limiting K⁺ permeability determinants the rate of RVD, and that this K⁺ permeability increases after growth-factor stimulation as predicted from the direct measurement of voltage-gated K⁺ conductance. The hydraulic permeability is ~70% greater in proliferating L2 cells than in quiescent cells. At 37°C, some RVD occurs in unstimulated L2 cells, and stimulated cells show faster and more complete shrinkage. These results are discussed with respect to the underlying membrane permeabilities and their relation to stimulated cell proliferation.