Cystic fibrosis transmembrane conductance regulator modulates synaptic chloride homeostasis in motoneurons of the rat spinal cord during neonatal development

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated Cl(-) channel functional in neonatal rat spinal motoneurons. The present study investigated the developmental (P1-P8) expression of CFTR, its impact on motoneuron excitability and Cl(-) homeostasis in relation to canonical Cl(-) transporters. The Cl(-) outward transporter KCC2 gene was upregulated in females over males and increased from P1 to P8. The gene activities of the Cl(-) inward transporter NKCC1 and CFTR were positively correlated and grew between P1 and P8. P1 motoneuronal somata were immunopositive for CFTR whose expression later (P8) extended to cell processes. KCC2 immunopositivity outlined somata and cell processes at P1 and P8. Electrophysiological recording with sharp electrodes showed that the CFTR blocker glibenclamide increased motoneuron input resistance, suggesting functional CFTR in P1-P8 motoneurons. Whole cell patch-clamping of spinal motoneurons to study CFTR contribution to postnatal synaptic Cl(-) regulation indicated that glibenclamide or the selective CFTR blocker diphenylamine-2,2'-dicarboxylic acid produced a negative shift in GABA/glycine reversal potential (E(GABA/Gly) ) of spontaneously occurring synaptic events measured after block of excitatory transmission. A similar effect on E(GABA/Gly) was induced by the NKCC1 inhibitor bumetanide. A 3D reconstructed motoneuron model suggested that CFTR activity contributes to set the E(GABA/Gly) positive to the resting potential. The functional outcome of these Cl(-) mediated synaptic events depended not only on the postnatal age of the animal but also on their timing with respect to the excitatory synaptic signals. We propose that CFTR operated together with NKCC1 to produce depolarizing GABA/glycine mediated synaptic events.

Cystic Fibrosis and the Nervous System

“…[34][35][36][37] Although expression in epithelial cells has been studied most, immune cells, 38 49 Expression of CFTR in the nervous system is particularly intriguing because chloride transport is a well-known modulator of neuronal activity. 50 In addition, as highlighted further on, many of the features of CF could manifest due to nervous system dysfunction.…”

“…51,52 Additional studies found CFTR expression or activity (or both) in rodent dorsal root ganglion neurons, 53 hypothalamic neurons, 54 and motor neurons. 37 In pigs, CFTR is expressed in both the peripheral and central nervous systems. 55,56 In humans, CFTR has been identified in parvocellular ganglion, 57 hypothalamic neurons, 58 spinal cord neurons, 59 ganglion cells of the heart, 60 and sympathetic ganglion.…”

“…Ostroumov et al 37 used CFTR inhibitors and computer modeling to demonstrate that CFTR modifies the excitability of motor neurons in the rat spinal cord. The authors went on to speculate that exaggerated neuronal excitability in individuals with CF might contribute to an increased incidence of seizures following lung transplantation.…”

Cystic Fibrosis Transmembrane Conductance Regulator Protein (CFTR) Expression in the Developing Human Brain

“…It has also been shown that CFTR plays a role in postsynaptic inhibition of motor neurons from the trigeminal motor nucleus during rapid-eye-movement (REM) sleep (Morales et al 2011). Recently, Ostroumov and colleagues observed that the gene activities of the chloride inward transporter, NKCC1, and CFTR were positively correlated postnatally and, using different blockers for these channels, demonstrated that inhibition of CFTR or NKCC1 activity produced a negative shift in GABA/glycine reversal potential of spontaneously occurring synaptic events measured after block of excitatory transmission, suggesting that CFTR operated together with NKCC1 to produce depolarizing GABA/glycinemediated synaptic events (Ostroumov et al 2011). The importance of chloride in the control of neuronal migration and differentiation is well known (Ben-Ari 2006) and, as with NKCC1, CFTR may also play a role in these processes.…”

Maturation of Inhibitory Synaptic Transmission in the Spinal Cord: Role of the Brain Stem and Contribution to the Development of Motor Patterns

“…In contrast, small glial cells surrounding MNs and dorsal root ganglion neurons are strongly positive (Kanaka et al, 2001). In addition to NKCC1, the anion exchanger (AE3; Gonzalez-Islas et al, 2009, in the chick embryo) and the cystic fibrosis transmembrane conductance regulator (CFTR; Ostroumov et al, 2010) are likely to also accumulate chloride in immature MNs. In addition to NKCC1, the anion exchanger (AE3; Gonzalez-Islas et al, 2009, in the chick embryo) and the cystic fibrosis transmembrane conductance regulator (CFTR; Ostroumov et al, 2010) are likely to also accumulate chloride in immature MNs.…”