A transient outward current in NG108-15 neuroblastoma x glioma hybrid cells.
Outward currents were recorded from voltage-clamped NG108-15 mouse neuroblastoma X rat glioma hybrid cells, differentiated with prostaglandin E1. Depolarising voltage steps from -70 mV, evoked a transient outward current from a threshold of -30 mV. The outward current showed complete inactivation at potentials positive to -10 mV. Inactivation was removed by hyperpolarisation with half-inactivation at -53 mV. The time course of the inactivation could be best fitted by two exponentials with mean time constants of 280 ms and 1.6 s at +80 mV. Tail current measurements showed a shift in the reversal potential with changes in external K+ concentration, consistent with K+ as the current-carrying ion. The outward current amplitude was reversibly reduced by 4-aminopyridine, and the time course of inactivation modified. In the presence of other K+ channel blockers (tetraethylammonium, barium and tetrahydroaminoacridine) the amplitude of the outward current was also reversibly reduced, but with a negligible effect on its time course. The current was unaffected by dendrotoxin, d-tubocurarine, apamin, Cd2+ and Ni2+, and by replacing external Ca2+ with Co2+ or Mg2+. In current clamp, action potential duration was greatly increased by 4-aminopyridine. The findings show that the NG108-15 cell line displays a transient outward current that resembles IK(A) but with a higher than usual threshold and relatively slow inactivation, and that this current is likely to be important for action potential repolarisation.
Robbins
J
J
Department of Pharmacology, University College London, UK.
Sim
J A
JA
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials; D000320:Adrenergic Fibers / Q000502:physiology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004546:Elapid Venoms / Q000494:pharmacology; D005910:Glioma / Q000503:physiopathology*; D006822:Hybrid Cells; D008564:Membrane Potentials; D009447:Neuroblastoma / Q000503:physiopathology*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D013619:Tacrine / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors; D014407:Tumor Cells, Cultured
D004546:Elapid Venoms; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D013619:Tacrine; D019789:Tetraethylammonium; C020273:dendrotoxin; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium