FUNCTIONAL CHANGES IN POTASSIUM CONDUCTANCES OF THE HUMAN NEUROBLASTOMA CELL LINE SH-SY5Y DURING IN VITRO DIFFERENTIATION. Patrizia TOSETTI, Vanni TAGLIETTI and Mauro TOSELLI. Istituto di Fisiologia Generale, Universita' di Pavia, Via Forlanini 6, I- 27100, Pavia, Italy.
APStracts 4:276N, 1997.
ABSTRACT
1. 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, using the whole-cell variant of the patch-clamp technique. 2. Voltage steps to depolarizing potentials from a holding level of -90 mV elicited, in both undifferentiated and differentiated cells, outward potassium currents which 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 volatge-dependent manner. 3. 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/cm2. Steady-state half inactivation potential was -13.8 mV and about 10 % of the current was resistant to inactivation. Both activation and inactivation kinetics were voltage-dependent. 4. 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/cm2. Steady-state half inactivation potential was -9.7 mV and about 37 % of the current was resistant to inactivation. Both activation and inactivation kinetics were voltage-dependent. 5. 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. 

Received 19 May 1997; accepted in final form 25 September 1997.
APS Manuscript Number J412-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997