Am J Physiol Cell Physiol Journal of Applied Physiology
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Am J Physiol Cell Physiol 270: C1131-C1144, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 270, Issue 4 C1131-C1144, Copyright © 1996 by American Physiological Society

ARTICLES

Potential-dependent block of human delayed rectifier K+ channels by internal Na+

S. Johansson, A. K. Sundgren and U. Kahl
Department of Neurochemistry and Neurotoxicology, Stockholm University, Sweden.

The delayed rectifier K+ currents in differentiated human SH-SY5Y neuroblastoma cells were characterized with tight-seal recording techniques. Activation and inactivation parameters were measured. At high positive potentials, the current showed a marked rectification, causing a region of negative slope conductance in the current vs. potential curve. The rectification depended markedly on the pipette Na+ concentration. Without Na+, no rectification was observed, whereas with high Na+ (20-60 mM), a marked rectification was always observed. Tail current measurements showed a fast ( < 400 microseconds) block of K+ currents in the presence of internal Na+. With 60 mM Na+ in the pipette 8% of the K+ current was blocked at 0 mV, 27% at +20 mV, and 82% at +100 mV. Similar degrees of block were often seen with 30 mM Na+ in the pipette. The submembrane Na+ concentration in intact cells was estimated, on the basis of the reversal of Na+ current, to be approximately 15 mM. Single-channel K+ currents, in the cell-attached configuration, showed a conductance of approximately 20 pS at 40-60 mV above rest but showed rectification at high potentials.


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