Tyrosine Kinases Open Lymphocyte Chloride Channels
Osmotic swelling of lymphocytes opens outwardly rectifying Cl- channels (ORCC) through the src-like kinase p56lck. The central role of this tyrosine protein kinase has been shown by genetic and pharmacologic manipulation of the enzyme. Furthermore, p56lck activates ORCC independently of cell volume increase. ORCC in lymphocytes and epithelial cells from cystic fibrosis (CF) patients are resistant to activation by cAMP. However, osmotic swelling as well as intracellular purified p56lck can activate ORCC in CF lymphocytes. In non-CF lymphocytes ORCC is opened by either, intracellular cAMP, p56lck or by osmotic swelling. Osmotic activation of ORCC can be blocked by the tyrosine kinase inhibitor lavendustin in both cell types. Regulation of ORCC by p56lck thus represents an alternative pathway of stimulating membrane chloride conductance that is left functional in cystic fibrosis. In addition to osmoregulation these mechanisms could play a major role when cells actively change their volume, i.e. during proliferation and apoptosis. Activation of the tyrosine kinase p56lck is an important regulatory step for opening of chloride channels in lymphocytes.