Inhibiting and stimulating effect of amiloride on potential-dependent cation channels in K562 cells

Non-voltage-gated ion channels play an essential role in cellular signalling and ionic homeostasis in nonexcitable cells. The patch clamp method in cell-attached configuration was used to search for the effects of amiloride and gadolinium (Gd3+) exerted on two types of voltage-insensitive cationic channels in plasma membrane of human leukemia K562 cells: Na-selective channels activated by actin disassembly, and mechanosensitive channels. Here we demonstrate that amiloride in high concentrations (1 mM) caused a full inhibition of mechanosensitive channels in K562 cells similarly to Gd3+ effect in micromolecular concentration range. Na-selective channels controlled by actin dynamics were shown to be unaffected by Gd3+ similarly as by amiloride. We also found that application of amiloride to the extracellular surface of membrane patch resulted in a significant increase in the activity of sodium channels. This unexpected stimulatory effect of amiloride may represent an unknown mechanism of activation of non-voltage-gated sodium channels. The data show an essential difference of the activation and blockage of these types of cation-selective channels.