Kv1.1-containing channels are critical for temporal precision during spike initiation

Low threshold, voltage-gated potassium currents (I-k1) are widely expressed in auditory neurons that can fire temporally precise action potentials (APs). In the medial nucleus of the trapezoid body (MNTB), channels containing the K(v)1.1 subunit (encoded by the Kcna1 gene) underlie I-k1. Using pharmacology, genetics and whole cell patch-clamp recordings in mouse brain slices, we tested the role of I-k1 in limiting AP latency-variability (jitter) in response to trains of single inputs at moderate to high stimulation rates. With dendrotoxin-K (DTX-K, a selective blocker of K(v)1.1-containing channels), we blocked I-k1 maximally (approximate to 80% with 100 nM DTX-K) or partially (approximate to 50% with 1-h incubation in 3 nM DTX-K). I-k1 was similar in 3 nM DTX-K-treated cells and cells from Kcna1(-/-) mice, allowing a comparison of these two different methods of I-k1 reduction. In response to current injection, I-k1 reduction increased the temporal window for AP initiation and increased jitter in response to the smallest currents that were able to drive APs. While 100 nM DTX-K caused the largest increases, latency and jitter in Kcna1(-/-) cells and in 3 nM DTX-K-treated cells were similar to each other but increased compared with +/+. The near-phenocopy of the Kcna1(-/-) cells with 3 nM DTX-K shows that acute blockade of a subset of the K(v)1.1-containing channels is functionally similar to the chronic elimination of all K(v)1.1 subunits. During rapid stimulation (100-500 Hz), I-k1 reduction increased jitter in response to both large and small inputs. These data show that I-k1 is critical for maintaining AP temporal precision at physiologically relevant firing rates.