Apparent change in ion selectivity caused by changes in intracellular K(+) during whole-cell recording.
In whole-cell recordings from HEK293 cells stably transfected with the delayed rectifier K(+) channel Kv2.1, long depolarizations produce current-dependent changes in [K(+)](i) that mimic inactivation and changes in ion selectivity. With 10 mM K(o)(+) or K(i)(+), and 140-160 mM Na(i,o)(+), long depolarizations shifted the reversal potential (V(R)) toward E(Na). However, similar shifts in V(R) were observed when Na(i,o)(+) was replaced with N-methyl-D-glucamine (NMG(+))(i, o). In that condition, [K(+)](o) did not change significantly, but the results could be quantitatively explained by changes in [K(+)](i). For example, a mean outward K(+) current of 1 nA for 2 s could decrease [K(+)](i) from 10 mM to 3 mM in a 10 pF cell. Dialysis by the recording pipette reduced but did not fully prevent changes in [K(+)](i). With 10 mM K(i,o)(+), 150 mM Na(i)(+), and 140 mM NMG(o)(+), steps to +20 mV produced a positive shift in V(R), as expected from depletion of K(i)(+), but opposite to the shift expected from a decreased K(+)/Na(+) selectivity. Long steps to V(R) caused inactivation, but no change in V(R). We conclude that current-dependent changes in [K(+)](i) need to be carefully evaluated when studying large K(+) currents in small cells.
Frazier
C J
CJ
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA. cjf2@po.cwru.edu
George
E G
EG
Jones
S W
SW
D055592:Biophysical Phenomena; D001703:Biophysics; D002460:Cell Line; D051668:Delayed Rectifier Potassium Channels; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D051669:Shab Potassium Channels; D012964:Sodium / Q000378:metabolism; D014162:Transfection
D051668:Delayed Rectifier Potassium Channels; C496988:KCNB1 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins; D051669:Shab Potassium Channels; D012964:Sodium