Elimination of the Fast Transient in Superior Cervical Ganglion Neurons with Expression of KV4.2W362F: Molecular Dissection ofIA

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Abstract
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,IAf, in sympathetic neurons and to explore the functional role ofIAfin shaping action potential waveforms and controlling repetitive firing patterns. Using the biolistic gene gun, cDNAs encoding a dominant negative mutant Kv4.2 α-subunit (Kv4.2W362F) and enhanced green fluorescent protein (EGFP) were introduced into rat sympathetic neuronsin vitro. Whole-cell voltage-clamp recordings obtained from EGFP-positive cells revealed thatIAfis selectively eliminated in cells expressing Kv4.2W362F, demonstrating that Kv4 α-subunits underlieIAfin sympathetic neurons. In addition,IAfdensity 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 thatIAfplays a pivotal role in regulating excitability. Expression of Kv4.2W362F and elimination ofIAfalso 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 ofIAfincreases the percentage of adapting cells by shifting phasic cells to the adapting firing pattern, and increasedIAfdensity reduces the number of adapting cells.