ИСТИНА

Non-voltage-gated sodium channels were identified as one of the main Na+-transporting pathways in cells of blood origin, including leukemia-lymphoma cell lines. Physiologycal mechanisms modulating Na+ permeability in blood cells remain to be elucidated. Proteolytic cleavage in extracellular domain was reported to be critical for canonical ENaC function in renal epithelia. Here, we tested the effect of serine protease trypsin on membrane currents in K562 cells which provide a unique model to analyze single channel behaviour in whole-cell patch-clamp experiments. We found that Na+ channel activity drastically increased in response to extracellular application of trypsin (5 g/ml). An involvement of proteolytic activity of trypsin in channel opening was confirmed in whole-cell experiments with soybean trypsin inhibitor (SBTI). Biophysical properties of Na+ channels activated by proteolytic cleavage or by actin disruptor cytochalasin D were practically identical; unitary conductance was 15 pS. Importantly, stabilization of F-actin with phalloidin did not prevent trypsin-induced channel activation. Single channel analysis clearly demonstrates that trypsin-induced currents did not blocked by amiloride and its derivative benzamil, known inhibitors of renal ENaC. Our observations imply common extracellular regulatory mechanism for canonical ENaCs and amiloride-insensitive ENaC-like channels in leukemia cells.