Functional changes in potassium conductances of the human neuroblastoma cell line SH-SY5Y during in vitro differentiation

The electrophysiological properties of voltage-dependent outward currents were investigated under voltage-clamp conditions in the human neuroblastoma cell line SH-SY5Y before and after in vitro differentiation with retinoic acid, by using the whole cell variant of the patch-clamp technique. Voltage steps to depolarizing potentials from a holding level of -90 mV elicited, in both undifferentiated and differentiated cells, outward potassium currents that were blocked by tetraethylammonium, but were unaffected by 4-aminopyridine, cadmium, and by shifts of the holding potentials to -40 mV. These currents activated rapidly and inactivated slowly in a voltage-dependent manner. In undifferentiated cells the threshold for current activation was about -30 mV, with a steady-state half activation potential of 19.5 mV, Maximum conductance was 4.3 nS and mean conductance density was 0.34 mS/cm(2). Steady-state half inactivation potential was -13.8 mV and similar to 10% of the current was resistant to inactivation. Both activation and inactivation kinetics were voltage dependent. In differentiated cells the threshold for current activation was about -20 mV, with a half potential for steady-state activation of 37.0 mV. Maximum conductance was 15.2 nS and mean conductance density was 0.78 mS/cm(2). Steady-state half inactivation potential was -9.7 mV and similar to 37% of the current was resistant to inactivation, Both activation and inactivation kinetics were voltage dependent. This diversity in potassium channel properties observed between undifferentiated and differentiated cells was related to differences in cell excitability. Under current-clamp conditions, the action potential repolarization rate in differentiated cells was about threefold faster than that of the abortive action potentials elicitable in undifferentiated cells. Furthermore, during prolonged stimulation, trains of spikes could be generated in some differentiated cells but not in undifferentiated cells.