The Tyrosine Kinase p56(lck) Mediates Activation of Swelling-induced Chloride Channels in Lymphocytes

Osmotic cell swelling activates Cl(−) channels to achieve anion efflux. In this study, we find that both the tyrosine kinase inhibitor herbimycin A and genetic knockout of p56(lck), a src-like tyrosine kinase, block regulatory volume decrease (RVD) in a human T cell line. Activation of a swelling-activated chloride current (I(Cl−swell)) by osmotic swelling in whole-cell patch-clamp experiments is blocked by herbimycin A and lavendustin. Osmotic activation of I(Cl−swell) is defective in p56(lck)-deficient cells. Retransfection of p56(lck) restores osmotic current activation. Furthermore, tyrosine kinase activity is sufficient for activation of I(Cl−swell). Addition of purified p56(lck) to excised patches activates an outwardly rectifying chloride channel with 31 pS unitary conductance. Purified p56(lck) washed into the cytoplasm activates I(Cl−swell) in native and p56(lck)-deficient cells even when hypotonic intracellular solutions lead to cell shrinkage. When whole-cell currents are activated either by swelling or by p56(lck), slow single-channel gating events can be observed revealing a unitary conductance of 25–28 pS. In accordance with our patch-clamp data, osmotic swelling increases activity of immunoprecipitated p56(lck). We conclude that osmotic swelling activates I(Cl−swell )in lymphocytes via the tyrosine kinase p56(lck).