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Biophys J, April 2000, p. 1872-1880, Vol. 78, No. 4

Apparent Change in Ion Selectivity Caused by Changes in Intracellular K+ during Whole-Cell Recording

Charles J. Frazier, Eric G. George, and Stephen W. Jones

Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106 USA

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 Ko+ or Ki+, and 140-160 mM Nai,o+, long depolarizations shifted the reversal potential (VR) toward ENa. However, similar shifts in VR were observed when Nai,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 Ki,o+, 150 mM Nai+, and 140 mM NMGo+, steps to +20 mV produced a positive shift in VR, as expected from depletion of Ki+, but opposite to the shift expected from a decreased K+/Na+ selectivity. Long steps to VR caused inactivation, but no change in VR. We conclude that current-dependent changes in [K+]i need to be carefully evaluated when studying large K+ currents in small cells.

Biophys J, April 2000, p. 1872-1880, Vol. 78, No. 4
© 2000 by the Biophysical Society   0006-3495/00/04/1872/09  $2.00


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