Silent voltage-gated potassium channel subunits (KS) interact selectively with members of the K2 channel family to modify their functional properties. The localization and functional roles of these silent subunits remain poorly understood. Mutations in the KS subunit, K8.2 (), lead to severe visual impairment in humans, but the basis of these deficits remains unclear. Here, we examined the localization, native interactions, and functional properties of K8.2-containing channels in mouse, macaque, and human photoreceptors of either sex. In human retina, K8.2 colocalized with K2.1 and K2.2 in cone inner segments and with K2.1 in rod inner segments. K2.1 and K2.2 could be coimmunoprecipitated with K8.2 in retinal lysates indicating that these subunits likely interact directly. Retinal K2.1 was less phosphorylated than cortical K2.1, a difference expected to alter the biophysical properties of these channels. Using voltage-clamp recordings and pharmacology, we provide functional evidence for Kv2-containing channels in primate rods and cones. We propose that the presence of K8.2, and low levels of K2.1 phosphorylation shift the activation range of K2 channels to align with the operating range of rod and cone photoreceptors. Our data indicate a role for K2/K8.2 channels in human photoreceptor function and suggest that the visual deficits in patients with mutations arise from inadequate resting activation of K channels in rod and cone inner segments. Mutations in a voltage-gated potassium channel subunit, K8.2, underlie a blinding inherited photoreceptor dystrophy, indicating an important role for these channels in human vision. Here, we have defined the localization and subunit interactions of K8.2 channels in primate photoreceptors. We show that the K8.2 subunit interacts with different Kv2 channels in rods and cones, giving rise to potassium currents with distinct functional properties. Our results provide a molecular basis for retinal dysfunction in patients with mutations in the gene encoding K8.2.

Brain-derived neurotrophic factor (BDNF) is abundantly expressed by both developing and adult rat visceral sensory neurons from the nodose ganglion (NG) in vivo and in vitro. We have previously shown that BDNF is released from neonatal NG neurons by activity and regulates dendritic development in their postsynaptic targets in the brainstem. The current study was carried out to examine the cellular and molecular mechanisms of activity-dependent BDNF expression in neonatal rat NG neurons, using our established in vitro model of neuronal activation by electrical field stimulation with patterns that mimic neuronal activity in vivo. We show that BDNF mRNA (transcript 4) increases over 3-fold in response to a 4-h tonic or bursting pattern delivered at the frequency of 6 Hz, which corresponds to the normal heart rate of a newborn rat. No significant increase in BDNF expression was observed following stimulation at 1 Hz. The latter effect suggests a frequency-dependent mechanism of regulated BDNF expression. In addition to BDNF transcript 4, which is known to be regulated by activity, transcript 1 also showed significant upregulation. The increases in BDNF mRNA were followed by BDNF protein upregulation of a similar magnitude after 24 h of stimulation at 6 Hz. Electrical stimulation-evoked BDNF expression was inhibited by pretreating neurons with the blocker of voltage-gated sodium channels tetrodotoxin and by removing extracellular calcium. Moreover, our data show that repetitive stimulation-evoked BDNF expression requires calcium influx through N-, but not L-type, channels. Together, our study reveals novel mechanisms through which electrical activity stimulates de novo synthesis of BDNF in sensory neurons, and points to the role of N-type calcium channels in regulating BDNF expression in sensory neurons in response to repetitive stimulation.

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