Molecular heterogeneity of the voltage-gated fast transient outward K+ current, I(Af), in mammalian neurons.

Recently, we identified four kinetically distinct voltage-gated K(+) currents, I(Af), I(As), I(K), and I(SS), 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 ( approximately 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.