IDENTIFICATION OF ENDOGENOUS OUTWARD CURRENTS IN THE HUMAN EMBRYONIC KIDNEY (HEK-293) CELL-LINE

Human embryonic kidney cells (HEK 293) are widely used as an expressio n system in studies of ion channels. However, their endogenous ionic c urrents remain largely unidentified. To characterize these currents, w e performed patch clamp experiments on this expression system. In whol e-cell voltage clamp mode, the HEK 293 cells showed mainly outward cur rents using physiological concentrations of Na+ and K+ and symmetric c oncentrations of Cl- (150 mM) across the plasma membranes. K+ currents contributed to a small portion of these outward currents, since a shi ft of the reversal potentials of only similar to 20 mV was seen with a change of extracellular K+ concentration from 3 to 150 mM. In contras t, the reversal potential shifted similar to 25 mV when extracellular Cl- was reduced to 50 mM, indicating that most of the outward currents are carried by Cl-. In inside-out patches, several distinct Cl- curre nts were identified. They were: (1) 350 pS Cl- current, which was volt age-activated and had a moderate outward rectification; (2) 240 pS Cl- current with a weak outward rectification; and (3) 55 pS Cl- current, which was voltage-activated, sensitive to DIDS, and showed a strong o utward rectification. Activation of these Cl- currents did not require an elevation of free Ca2+ level in the cytosol. Besides these three c urrents, we observed two other Cl- currents with much smaller conducta nces (25 and 16 pS, respectively). Two different K+ currents were seen in the HEK 293 cells, with one of them (125 pS) showing inward rectif ication and the other (70 pS) outward rectification. Moreover, a 50 pS cation channel was recorded in these cells. The presence of a variety of ion channels in the HEK 293 cells suggests that a great precaution needs to be taken when this expression system is used in studies of s everal similar ion channels. (C) 1998 Elsevier Science B.V. All rights reserved.