Regulation of Kv4.2 A-Type Potassium Channels in HEK-293 Cells by Hypoxia.

Yu-Qiang Liu,Wen-Xian Huang,Jiang-Jian Hu,Bi-Wen Peng,Xiao-Hua He,Jia-Wei Min,Russell M Sanchez

doi:10.3389/fncel.2014.00329

Abstract

We previously observed that A-type potassium currents were decreased and membrane excitability increased in hippocampal dentate granule cells after neonatal global hypoxia associated with seizures. Here, we studied the effects of hypoxia on the function and expression of Kv4.2 and Kv4.3 α subunit channels, which encode rapidly inactivating A-type K currents, in transfected HEK-293 cells to determine if hypoxia alone could regulate IA in vitro. Global hypoxia in neonatal rat pups resulted in early decreased hippocampal expression of Kv4.2 mRNA and protein with 6 or 12 h post-hypoxia. Whole-cell voltage-clamp recordings revealed that similar times after hypoxia (1%) in vitro decreased peak currents mediated by recombinant Kv4.2 but not Kv4.3 channels. Hypoxia had no significant effect on the voltage-dependencies of activation and inactivation of Kv4.2 channels, but increased the time constant of activation. The same result was observed when Kv4.2 and Kv4.3 channels were co-expressed in a 1:1 ratio. These data suggested that hypoxia directly modulates A-type potassium channels of the subfamily typically expressed in principal hippocampal neurons, and does so in a manner to decrease function. Given the role of IA to slow action potential firing, these data are consistent with a direct effect of hypoxia to decrease IA as a mechanism of increased neuronal excitability and promotion of seizures.

Highlights

Voltage-dependent potassium (Kv) channels have a role in many developmental nervous system diseases, such as learning and cognitive impairment and epilepsy (Lawson, 2000; Wulff et al, 2009)
HYPOXIA TREATMENT DECREASED Kv4.2 EXPRESSION IN RAT HIPPOCAMPUS First, we examined the expression of Kv4.2 and Kv4.3 after hypoxia treatment in neonatal rat pups
The levels of Kv4.2 mRNA and protein were significantly decreased by hypoxia treatment at each time point we tested (Figures 1A,B). 6, 12, and 24 h after the hypoxia treatment, Kv4.2 mRNA was decreased by 35% (n = 3, p < 0.05 vs. control), 68% (n = 3, p < 0.01 vs. control), and 84% (n = 3, p < 0.01 vs. control), respectively, and Kv4.2 protein was decreased by 22% (n = 3, p < 0.05 vs. control), 21% (n = 3, p < 0.05 vs. control), and 43% (n = 3, p < 0.01 vs. control), respectively

Summary

Introduction

Voltage-dependent potassium (Kv) channels have a role in many developmental nervous system diseases, such as learning and cognitive impairment and epilepsy (Lawson, 2000; Wulff et al, 2009). A-type potassium channels are abundantly expressed in neurons and serve a number of functions, including regulation of excitability, fast-spiking, neurotransmitter release, and control of neural networks in physiological and pathophysiological processes (Birnbaum et al, 2004). Kv channels are composed of pore-forming α proteins and auxiliary β subunits (Patel and Honore, 2001; Conforti et al, 2003a). Among the Kv4 α subunits (Kv4.1, Kv4.2, and Kv4.3), Kv4.2 and Kv4.3 underlie the somatodendritic A-type K+ currents in the central nervous system (CNS) (Huang et al, 2005), whereas, Kv4.1 mRNA levels are lower than Kv4.2 or Kv4.3 (Serodio and Rudy, 1998). Kv4.2 is mainly expressed in area CA1 pyramidal cells, and comprises the pore-forming subunit together with Kv4.3, whereas CA1 inhibitory interneurons express primarily Kv4.3 channels (Birnbaum et al, 2004). Downregulation of A-type K+ channel function in pyramidal neuron dendrites increases neuronal excitability (Bernard et al, 2004), and selective blockade of A-type potassium channel can cause seizures (Ruschenschmidt et al, 2006)

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Conclusion