Role of Actin Dynamics in the Control of Proteolytically Induced ENaC-Like Channel Activity in Human Leukemia Cells
摘要
Objective: Non-voltage-gated sodium-selective channels are one of the major sodium entry pathways responsible for rapid changes in sodium permeability in non-excitable cells. The activity of these channels may be associated with basic physiological or pathophysiological processes in cells of blood origin. Methods: In our previous studies, using various configurations of the patch-clamp method in human leukemia cell lines, the functional properties and regulatory mechanisms of amiloride-insensitive epithelial Na+-channels (ENaC-like channels) were investigated. Intracellular mechanisms of ENaC-like channel regulation were shown to be directly or indirectly associated with actin dynamics. New extracellular pathway of ENaC-like channel activation under the action of serine protease trypsin were found in K562 cells. Here we examined an involvement of actin rearrangements in the functioning of trypsin-activated ENaC-like channels in leukemia K562 cells. The activation of ENaC-like channels (unitary conductance of 15 pS) by application of trypsin to the extracellular membrane side was revealed in whole-cell and inside-out experiments. Single-channel whole-cell recording have demonstrated that the inclusion of phalloidin, a stabilizer of fibrillar actin, into intracellular pipette solution do not prevent the activation of sodium currents by trypsin. Results and Discussion: These observations indicate that actin disassembly is not involved in the proteolytic activation of ENaC-like channels. Nevertheless, as shown in inside-out experiments, polymerizing actin caused fast inactivation of the trypsin-induced channels. Conclusions: The data obtained reveal that extracellular proteolytic activation of ENaC-like channels is independent on actin dynamics whereas their inactivation could be induced by actin assembly.