Q. Hu et Yl. Shi, CHARACTERIZATION OF AN INWARD-RECTIFYING POTASSIUM CURRENT IN NG108-15 NEUROBLASTOMA X GLIOMA-CELLS, Pflugers Archiv, 433(5), 1997, pp. 617-625
By using the whole-cell patch-clamp technique, an inwardly rectifying
potassium current, which resembled the ''classic'' inward-rectifying p
otassium current (I-KIR) of other cells in terms of electrophysiologic
al and pharmacological properties, was identified in db-cAMP-different
iated NG108-15 cells. First, the current was dependent on voltage and
time. It could be elicited by applying an initial depolarizing prepuls
e and a subsequent hyperpolarizing command pulse to the cell. The ampl
itude of the current depended on both the prepulse and the command pul
se and increased with the hyperpolarization of the command pulse as we
ll as the depolarization and the prolongation of the prepulse. The act
ivation and inactivation of the current could be fitted well by single
-exponential functions and increased with the hyperpolarization of the
membrane. Second, the current was dependent on the extracellular pota
ssium concentration ([K+](o)). Elevation of [K+](o) resulted in a mark
ed increase in the cut-rent amplitude and a positive shift of the peak
-current/voltage curve as well as the reversal potential. A tenfold in
crease of [K+](o) introduced an approximate to 43-mV shift of the reve
rsal potential, indicating that the current was carried mainly by K+.
The conductance (g/g(Max)) of the current was also dependent on the [K
+](o) and increased with increases in [K+](o) in a manner approximatel
y proportional to the square-root of [K+](o). Finally, the current was
sensitive to Cs+ (1 mmol/l), Ba2+ (1 mmol/l) and quinidine (0.2 mmol/
l); whereas, two typical potassium channel inhibitors, tetraethylammon
ium (TEA) and 4-aminopyridine (4-AP), were weak blockers and reduced t
he current at high concentration (>10 mmol/l). It was also observed th
at the current was depressed by Cd2+ (1 mmol/l) and Co2+ (1 mmol/l) an
d increased by perfusing the cell with Ca2+-free solution. Thus, excep
t for the sensitivity to Cd2+, Co2+ and Ca2+, the current displayed mo
st of the hallmarks described for the ''classic'' I-KIR. In conclusion
, there appears to be a voltage-dependent I-KIR-type inward rectifier
in db-cAMP-differentiated NG108-15 cells.