Potential-dependent block of human delayed-rectifier k+ channels by
internal na+.
Johansson, Staffan, Anna K. Sundgren, and Ulrika Kahl.
Department of Neurochemistry and Neurotoxicology, Stockholm
University, S-106 91 Stockholm, Sweden
APStracts 2:0374C, 1995.
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-versus
-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 [mu]s) 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 basis of the reversal of Na+ current, to
about 15 mM. Single-channel K+ currents, in the cell-attached
configuration, showed a conductance of about 20 pS at 40-60 mV above
rest, but showed rectification at high potentials.
Received 7 July 1995; accepted in final form 18 September 1995.
APS Manuscript Number C411-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95