Influx of calcium through L‐type calcium channels in early postnatal regulation of chloride transporters in the rat hippocampus

Abstract

During the early postnatal period, GABA(B) receptor activation facilitates L-type calcium current in rat hippocampus. One developmental process that L-type current may regulate is the change in expression of the K(+)Cl(-) co-transporter (KCC2) and N(+)K(+)2Cl(-) co-transporter (NKCC1), which are involved in the maturation of the GABAergic system. The present study investigated the connection between L-type current, GABA(B) receptors, and expression of chloride transporters during development. The facilitation of L-type current by GABA(B) receptors is more prominent in the second week of development, with the highest percentage of cells exhibiting facilitation in cultures isolated from 7 day old rats (37.5%). The protein levels of KCC2 and NKCC1 were investigated to determine the developmental timecourse of expression as well as expression following treatment with an L-type channel antagonist and a GABA(B) receptor agonist. The time course of both chloride transporters in culture mimics that seen in hippocampal tissue isolated from various ages. KCC2 levels increased drastically in the first two postnatal weeks while NKCC1 remained relatively stable, suggesting that the ratio of the chloride transporters is important in mediating the developmental change in chloride reversal potential. Treatment of cultures with the L-type antagonist nimodipine did not affect protein levels of NKCC1, but significantly decreased the upregulation of KCC2 during the first postnatal week. In addition, calcium current facilitation occurs slightly before the large increase in KCC2 expression. These results suggest that the expression of KCC2 is regulated by calcium influx through L-type channels in the early postnatal period in hippocampal neurons.

Involvement of protein kinase C and protein kinase A in the enhancement of L-type calcium current by GABAB receptor activation in neonatal hippocampus

“…Many inhibitory interneuron subtypes within the hippocampus utilize GABA to regulate the overall excitability of the hippocampus. Our laboratory has demonstrated that activation of GABA B receptors can enhance calcium influx through L-type calcium channels and attenuate calcium influx through N-type channels during development of the rat hippocampus (Carter and Mynlieff, 2004; Bray and Mynlieff, 2009). Using calcium imaging, a similar enhancement of calcium current by GABA B receptor activation was recently reported in hippocampal neurons isolated from embryonic tissue (Park et al, 2010).…”

“…Upon GABA B receptor activation, neuronal calcium channels can be directly regulated by either Gα or Gβγ subunits or they can be indirectly regulated by G-proteins through second messenger systems (for review see Catterall, 2000; Dolphin, 2003; Tedford and Zamponi, 2006). We have previously demonstrated that GABA B receptor activation can lead to an attenuation of N-type calcium current and the enhancement of L-type calcium current in hippocampal cultures obtained from neonatal rat pups (Carter and Mynlieff, 2004; Bray and Mynlieff, 2009). The variety of responses seen in primary hippocampal cultures is likely due to the heterogeneity of the neuron types present.…”

“…L-type calcium channels are located on the soma and dendrites of neurons and thus current through L-type channels regulates many processes including enzymatic activity, excitability, and gene expression (for review see Lipscombe, 2004; Pinato et al, 2009). For example, in neonatal hippocampus calcium influx through L-type calcium channels contributes to the regulation of expression of the K + Cl − co-transporter (Bray and Mynlieff, 2009). It is well known that the inhibition of N-type current by GABA B receptor activation in mammalian neurons is mediated by Gβγ subunits from the G i/o protein family, which are sensitive to pertussis toxin (PTX; Kleuss et al, 1991; Ikeda et al, 1996; Kajikawa et al, 2001; for review see Tedford and Zamponi, 2006).…”

Levels of 1.2 L-Type Channels Peak in the First Two Weeks in Rat Hippocampus Whereas 1.3 Channels Steadily Increase through Development

“…This peak of Ca V 1.2 expression correlates with the peak of calcium channel enhancement by GABA B receptor activation in the superior region of the hippocampus [32]. However, Park and colleagues [36] demonstrated a protein-protein interaction between the amino terminal of Ca V 1.3 and the carboxy terminal of the GABA B R2 subunit in adult hippocampus.…”

Effects of sex and chronic neonatal nicotine treatment on Na2+/K+/Cl− co-transporter 1, K+/Cl− co-transporter 2, brain-derived neurotrophic factor, NMDA receptor subunit 2A and NMDA receptor subunit 2B mRNA expression in the postnatal rat hippocampus

“…However, it is known that activation of presynaptic nAChRs by nicotine can increase GABA release (Alkondon et al, 1999, Radcliffe et al, 1999, Maggi et al, 2001), which may lead to an increase in Ca 2+ influx via L-type voltage gated Ca 2+ channels following GABA A R-mediated depolarization in immature neurons (Obrietan and van den Pol, 1995, Ganguly et al, 2001). This increase in Ca 2+ may then lead to an increase in KCC2 mRNA expression (Ganguly et al, 2001, Bray and Mynlieff, 2009). …”