Molecular heterogeneity of the voltage-gated fast transient outward K+ current, IAf, in mammalian neurons

Recently, we identified four kinetically distinct voltage-gated K+ currents, I-Af, I-As, I-K, and (ISS), in rat superior cervical ganglion (SCG) neurons and demonstrated that I-Af and I-As are differentially expressed in type I (I-Af, I-K, I-SS), type II (I-Af, I-As, I-K, I-SS), and type III (I-K, I-SS) SCG cells. In addition, we reported that I-Af is eliminated in most (similar to 70%) SCG cells expressing Kv4.2W362F, a Kv4 subfamily-specific dominant negative. The molecular correlate(s) of the residual I-Af, as well as that of I-As, I-K, and I-SS, however, are unknown. The experiments here were undertaken to explore the role of Kv1 alpha -subunits in the generation of voltage-gated K+ currents in SCG neurons. Using the Biolistics Gene Gun, cDNA constructs encoding a Kv1 subfamily-specific dominant negative, Kv1.5W461F, and enhanced green fluorescent protein (EGFP) were introduced into SCG neurons. Whole-cell recordings from EGFP-positive Kv1.5W461F-expressing cells revealed a selective decrease in the percentage of type I cells and an increase in type III cells, indicating that I-Af is gated by Kv1 alpha -subunits in a subset of type I SCG neurons. I-Af is eliminated in all SCG cells expressing both Kv1.5W461F and Kv4.2W362F. I-Af tau (decay) values in Kv1.5W461F-expressing and Kv4.2W362F-expressing type I cells are significantly different, revealing that Kv1 and Kv4 alpha -subunits encode kinetically distinct I-Af channels. Expression of Kv1.5W461F increases excitability by decreasing action potential current thresholds and converts phasic cells to adapting or tonic firing. Interestingly, the molecular heterogeneity of I-Af channels has functional significance because Kv1- and Kv4-encoded I-Af play distinct roles in the regulation of neuronal excitability.