Expression of the dominant negative mutant Kv4.2W362F selectively eliminated the fast transient outward K+ current (I_Af) in rat sympathetic neurons, increasing input resistance and altering firing.
Kv4 alpha-subunits underlie the fast transient outward K+ current in sympathetic neurons, which plays a pivotal role in regulating neuronal excitability and repetitive firing patterns.
Electrophysiological and molecular studies have revealed considerable heterogeneity in voltage-gated K(+) currents and in the subunits that underlie these channels in mammalian neurons. At present, however, the relationship between native K(+) currents and cloned subunits is poorly understood. In the experiments here, a molecular genetic approach was exploited to define the molecular correlate of the fast transient outward K(+) current, I(Af), in sympathetic neurons and to explore the functional role of I(Af) in shaping action potential waveforms and controlling repetitive firing patterns. Using the biolistic gene gun, cDNAs encoding a dominant negative mutant Kv4.2 alpha-subunit (Kv4.2W362F) and enhanced green fluorescent protein (EGFP) were introduced into rat sympathetic neurons in vitro. Whole-cell voltage-clamp recordings obtained from EGFP-positive cells revealed that I(Af) is selectively eliminated in cells expressing Kv4.2W362F, demonstrating that Kv4 alpha-subunits underlie I(Af) in sympathetic neurons. In addition, I(Af) density is increased significantly in cells overexpressing wild-type Kv4.2. In cells expressing Kv4.2W362F, input resistances are increased and (current) thresholds for action potential generation are decreased, demonstrating that I(Af) plays a pivotal role in regulating excitability. Expression of Kv4.2W362F and elimination of I(Af) also alters the distribution of repetitive firing patterns observed in response to a prolonged injection of depolarizing current. The wild-type superior cervical ganglion is composed of phasic, adapting, and tonic firing neurons. Elimination of I(Af) increases the percentage of adapting cells by shifting phasic cells to the adapting firing pattern, and increased I(Af) density reduces the number of adapting cells.
Malin et al. (Sat,) reported a other. Expression of dominant negative mutant Kv4.2 alpha-subunit (Kv4.2W362F) vs. Wild-type Kv4.2 overexpression or wild-type neurons was evaluated on Elimination of I(Af) and changes in excitability and firing patterns. Expression of the dominant negative mutant Kv4.2W362F selectively eliminated the fast transient outward K+ current (I_Af) in rat sympathetic neurons, increasing input resistance and altering firing.