Sodium channel activity in leukemia cells is directly controlled by actin polymerization

The actin cytoskeleton has been shown to be involved in the regulation of s odium-selective channels in nonexcitable cells. However, the molecular mech anisms underlying the changes in channel function remain to be defined. In the present work, inside-out patch experiments were employed to elucidate t he role of submembranous actin dynamics in the control of sodium channels i n human myeloid leukemia K562 cells. We found that the application of cytoc halasin D to the cytoplasmic surface of membrane fragments resulted in acti vation of non-voltage-gated sodium channels of 12 picosiemens conductance. Similar effects could be evoked by addition of the actin-severing protein g elsolin to the bath cytosol-like solution containing 1 muM [Ca2+](i). The s odium channel activity induced by disassembly of submembranous microfilamen ts with cytochalasin D or gelsolin could be abolished by intact actin added to the bath cytosol-like solution in the presence of 1 mM MgCl2, to induce actin polymerization, In the absence of MgCl2, addition of intact actin di d not abolish the channel activity. Moreover, the sodium currents were unaf fected by heat-inactivated actin or by actin whose polymerizability was str ongly reduced by cleavage with specific Escherichia coli A2 protease ECP32, Thus, the inhibitory effect of actin on channel activity was observed only under conditions promoting rapid polymerization. Taken together, our data show that sodium channels are directly controlled by dynamic assembly and d isassembly of submembranous F-actin.