Functional expression of an inactivating potassium channel (Kv4.3) in a mammalian cell line

Objective: The goal of this study was to characterize the electrophysiologi cal properties of the Kv4.3 channels expressed in a mammalian cell line. Me thods: Currents were recorded using the whole-cell voltage clamp technique. Results: The threshold for activation of the expressed Kv4.3 current was a pproximately -30 mV. The dominant time constant for activation was 1.71+/-0 .16 ms (n=10) at +60 mV. The current inactivated, this process being incomp lete, resulting in a sustained level which contributed 15+/-2% (n=25) of th e total current. The time course of inactivation was fit by a biexponential function, the fast component contributing 74+/-5% (n=9) to the overall ina ctivation. The fast time constant was voltage-dependent [27.6+/-2.0 ms at 60 mV(n=10) versus 64.0+/-3.6 ms at 0 mV (n=10); P<0.01], whereas the slow was voltage-independent [142+/-15 ms at +60 mV(n=10) versus 129+/-33 ms at 0 mV (n=6) P>0.05]. The voltage-dependence of inactivation exhibited midpoi nt and slope values of -26.9+/-1.5 mV and 5.9+/-0.3 mV (n=21). Recovery fro m inactivation was faster at more negative membrane potentials [203+/-17 ms (n=13) and 170+/-19 ms (n=4), at -90 and -100 mV]. Bupivacaine block of Kv 4.3 channels was not stereoselective (K-D similar to 31 mu M). Conclusions: The functional profile of Kv4.3 channels expressed in Ltk(-) cells corresp onds closely to rat I-TO, although differences in recovery do not rule out association with accessory subunits. Nevertheless, the sustained component needs to be considered with respect to native I-TO. (C) 1999 Elsevier Scien ce B.V. All rights reserved.