Heterologous Expression of the K_v3.1 Potassium Channel Eliminates Spike Broadening and the Induction of a Depolarizing Afterpotential in the Peptidergic Bag Cell Neurons

Abstract

The bag cell neurons of Aplysia are a cluster of cells that control egg laying behavior. After brief synaptic stimulation, they depolarize and fire spontaneously for up to 30 min. During the first few seconds of this afterdischarge, the action potentials of the bag cell neurons undergo pronounced broadening. Single bag cell neurons in culture also show spike broadening in response to repeated depolarizations. This broadening is frequencydependent and associated with the induction of a depolarizing afterpotential lasting minutes. In some neurons the depolarizing afterpotential is sufficient to trigger spontaneous firing. To test the possibility that spike broadening during stimulation is required to trigger the depolarizing afterpotential, we eliminated frequency-dependent broadening by heterologous expression of the Kv3.1 potassium channel. This channel has rapid activation and deactivation kinetics and no use-dependent inactivation. Expression of Kv3.1 prevented spike broadening and also eliminated the depolarizing afterpotential. Measurements of the integral of calcium current during voltage commands, which simulated the action potentials of the control neurons and those expressing Kv3.1, indicate that spike broadening produces up to a fivefold increase in calcium entry. Manipulations that limit calcium entry during action potentials or chelation of intracellular calcium using BAPTA AM prevented the induction of the depolarizing afterpotential. We conclude that spike broadening is essential for the induction of the depolarizing afterpotential probably by regulating calcium influx and suggest that one of the physiological roles of spike broadening may be to regulate long-term changes in neuronal excitability.

Opposite Actions of Brain-Derived Neurotrophic Factor and Neurotrophin-3 on Firing Features and Ion Channel Composition of Murine Spiral Ganglion Neurons

“…Kv3.1, which can contribute to limiting the action potential duration and increasing accommodation (Whim and Kaczmarek, 1998;Rudy et al, 1999), like K C a and Kv1.1, was localized predominately to the basal spiral ganglion neurons in control cultures (Fig. 7).…”

Firing features and potassium channel content of murine spiral ganglion neurons vary with cochlear location

“…5d). One channel type consistently implicated in increasing the rate of action potential repolarization and the magnitude of the subsequent afterhyperpolarization is the high-voltage activated K ϩ subunit, Kv3.1 (Whim and Kaczmarek, 1998;Rudy et al, 1999). These channels activate at relatively positive potentials, display very rapid deactivation kinetics, and are highly expressed in neurons that can fire at high frequencies with little or no accommodation during maintained trains of synaptic inputs (Gan and Kaczmarek, 1998;Wang et al, 1998b;.…”

Regulation of the timing of MNTB neurons by short-term and long-term modulation of potassium channels

“…Further experimental evidence that an increase in Kv3.1 levels promotes the ability of neurons to Wre at higher frequencies has come from experiments in which the Kv3.1 gene has been transfected into neurons that are normally incapable of high-frequency Wring (Whim and Kaczmarek, 1998). Fig.…”

“…Taken together, these Wndings indicate that the Kv3.1 channel is required for neurons such as those of the MBTB to Wre at high rates and that the level of Kv3.1 determines the upper frequency at which neurons are able to follow repetitive stimulation. Outward potassium currents recorded from a control bag cell neuron (left) and a GFP-positive bag cell neuron that had been co-injected with a vector for GFP expression together with pNEX-Kv3.1, which produces overexpression of Kv3.1 current (right) (Whim and Kaczmarek, 1998). The neurons were held at ¡60 mV and depolarized for 1 s to ¡25, ¡15 and ¡5 mV.…”