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Papers by Daniel Feldman

Annals of Neurology, Mar 27, 2015

Objective-To describe the unique phenotype and genetic findings in a 57-year-old female with a ra... more Objective-To describe the unique phenotype and genetic findings in a 57-year-old female with a rare form of congenital myasthenic syndrome (CMS) associated with longstanding muscle fatigability, and to investigate the underlying pathophysiology. Methods-We used whole-cell voltage clamping to compare the biophysical parameters of wildtype and Arg1457His-mutant Na v 1.4. Results-Clinical and neurophysiological evaluation revealed features consistent with CMS. Sequencing of candidate genes indicated no abnormalities. However, analysis of SCN4A, the gene encoding the skeletal muscle sodium channel Na v 1.4, revealed a homozygous mutation predicting an arginine-to-histidine substitution at position 1457 (Arg1457His), which maps to the channel's voltage sensor, specifically D4/S4. Whole-cell patch clamp studies revealed that the mutant required longer hyperpolarization to recover from fast inactivation, which produced a profound use-dependent current attenuation not seen in the wild type. The mutant channel also had a marked hyperpolarizing shift in its voltage dependence of inactivation as well as slowed inactivation kinetics.

Neurology, Apr 6, 2015

Objective: To describe the unique phenotype and genetic findings in a 57-year-old female with a r... more Objective: To describe the unique phenotype and genetic findings in a 57-year-old female with a rare form of congenital myasthenic syndrome (CMS) associated with longstanding muscle fatigability, and to investigate the underlying pathophysiology. Methods: We used whole-cell voltage clamping to compare the biophysical parameters of wild-type and Arg1457His-mutant Na v 1.4. Results: Clinical and neurophysiological evaluation revealed features consistent with CMS. Sequencing of candidate genes indicated no abnormalities. However, analysis of SCN4A, the gene encoding the skeletal muscle sodium channel Na v 1.4, revealed a homozygous mutation predicting an arginine-to-histidine substitution at position 1457 (Arg1457His), which maps to the channel's voltage sensor, specifically D4/S4. Whole-cell patch clamp studies revealed that the mutant required longer hyperpolarization to recover from fast inactivation, which produced a profound use-dependent current attenuation not seen in the wild type. The mutant channel also had a marked hyperpolarizing shift in its voltage dependence of inactivation as well as slowed inactivation kinetics. Interpretation: We conclude that Arg1457His compromises muscle fiber excitability. The mutant fast-inactivates with significantly less depolarization, and it recovers only after extended hyperpolarization. The resulting enhancement in its use dependence reduces channel availability, which explains the patient's muscle fatigability. Arg1457His offers molecular insight into a rare form of CMS precipitated by sodium channel inactivation defects. Given this channel's involvement in other muscle disorders such as paramyotonia congenita and hyperkalemic periodic paralysis, our study exemplifies how variations within the same gene can give rise to multiple distinct dysfunctions and phenotypes, revealing residues important in basic channel function.

Proceedings of the National Academy of Sciences, 1987

Blockade of Ca2+ channels by omega-conotoxin GVIA, a 27 amino acid peptide from the venom of the ... more Blockade of Ca2+ channels by omega-conotoxin GVIA, a 27 amino acid peptide from the venom of the marine snail Conus geographus, was investigated with patch-clamp recordings of whole-cell and unitary currents in a variety of cell types. In dorsal root ganglion neurons, the toxin produces persistent block of L- and N-type Ca2+ channels but only transiently inhibits T-type channels. Its actions appear to be neuron-specific, since it blocks high-threshold Ca2+ channels in sensory, sympathetic, and hippocampal neurons of vertebrates but not in cardiac, skeletal, or smooth muscle cells. Block occurs through direct interaction of the toxin with an external site closely associated with the Ca2+ channel, without apparent involvement of a second messenger or dependence on channel gating. The tissue and channel-type specificity and the directness and slow reversibility of the block are features that favor use of omega-conotoxin as a tool for purifying particular neuronal Ca2+ channels and defi...

Journal of Experimental Biology, 2002

SUMMARYCAATCH1 functions both as an amino-acid-gated cation channel and as a cation-dependent, pr... more SUMMARYCAATCH1 functions both as an amino-acid-gated cation channel and as a cation-dependent, proline-preferring, nutrient amino acid transporter in which the two functions are thermodynamically uncoupled. This study focuses on the ionic channel aspect, in which a Tyr147 (wild type) to Phe147 (Y147F) site-directed mutation was investigated by steady-state electrophysiological measurements in the Xenopus laevisoocyte expression system. This tyrosine residue is conserved within the third transmembrane domain in members of the Na+:neurotransmitter transporter family (SNF), where it plays a role in binding pharmacological ligands such as cocaine to the serotonin (SERT), dopamine (DAT) and norepinephrine (NET) transporters. Epithelial CAATCH1 is a member of the SNF family. The results show that amino acid ligand-gating selectivity and current magnitudes in Na+- and K+-containing media are differentially altered in CAATCH1 Y147F compared with the wild type. In the absence of amino acid l...

Journal of Experimental Biology, 1986

Ca2+ channels allow passage of Ca2+ ions into the cytoplasm through a selective pore which is ope... more Ca2+ channels allow passage of Ca2+ ions into the cytoplasm through a selective pore which is opened in response to depolarization of the cell membrane (for reviews see Hagiwara & Byerly, 1981, 1983; Tsien, 1983; Reuter, 1983). The Ca2+ flux creates a net inward, depolarizing current and the resulting accumulation of Ca2+ in the cytoplasm can act as a chemical trigger for secretion of hormones and neurotransmitters, contraction of muscle and a-variety of other Ca2+-sensitive events. Thus, upon sensing membrane potential changes, Ca2+ channels simultaneously generate an electrical signal while directly creating an intracellular chemical messenger. This dual ability is unique among the family of ion channels and allows the Ca2+ channel to play a variety of roles in excitation-secretion and excitation-contraction coupling. It has now become clear that versatility of function is reflected by diversity of the types of Ca2+ channels on the membrane of individual cells. This article descri...

The Journal of Neuroscience, 1988

B cells and C cells in frog lumbar sympathetic ganglia are specifically innervated by preganglion... more B cells and C cells in frog lumbar sympathetic ganglia are specifically innervated by preganglionic B fibers and C fibers, respectively. To explore the mechanisms underlying the formation of these specific synapses, electrophysiological studies were made of sprouting and regenerating synaptic connections following interruption of the preganglionic pathways. Studies were also made of developing connections in tadpole ganglia. After partial denervation (by selective interruption of B fibers), the C fibers sprouted and innervated B cells. When B fibers regenerated, they reinnervated B cells only, and within several weeks, C fiber synapses on B cells were no longer found. After complete denervation (by interruption of both B and C fibers) specific synaptic connections were eventually restored. At least 2 experimentally separable processes underlie this specificity: First, there is a preference for appropriate connections from the outset of reinnervation, seen even in the absence of comp...

MethodsX, 2014

Research involving recombinant voltage-gated sodium (Na v) channels has unique challenges. Multip... more Research involving recombinant voltage-gated sodium (Na v) channels has unique challenges. Multiple factors contribute, but undoubtedly at the top of the list is these channels' DNA instability. Once introduced into bacterial hosts, Na v channel plasmid DNA will almost invariably emerge mutagenized and unusable, unless special conditions are adopted. This is particularly true for Na v 1.1 (gene name SCN1A), Na v 1.2 (SCN2A), and Na v 1.6 (SCN8A), but less so for Na v 1.4 (SCN4A) and Na v 1.5 (SCN5A) while other Na v channel isoforms such as Na v 1.7 (SCN9A) lie in between. The following recommendations for Na v plasmid DNA amplification and preparation address this problem. Three points are essential: Bacterial propagation using Stbl2 cells at or below 30 8C. Bias toward slow-growing, small bacterial colonies. Comprehensive sequencing of the entire Na v channel coding region.

Annals of neurology, Jan 23, 2015

Objective: To describe the unique phenotype and genetic findings in a 57-year old female with a r... more Objective: To describe the unique phenotype and genetic findings in a 57-year old female with a rare form of congenital myasthenic syndrome (CMS) associated with longstanding muscle fatigability, and to investigate the underlying pathophysiology. Methods: We used whole-cell voltage clamping to compare the biophysical parameters of wild-type and Arg1457His-mutant Nav1.4. Results: Clinical and neurophysiological evaluation revealed features consistent with CMS. Sequencing of candidate genes indicated no abnormalities. However, analysis of SCN4A, the gene encoding the skeletal muscle sodium channel Nav 1.4, revealed a homozygous mutation predicting an arginine-to-histidine substitution at position 1457 (Arg1457His), which maps to the channel's voltage sensor, specifically D4/S4. Whole-cell patch clamp studies revealed that the mutant required longer hyperpolarization to recover from fast inactivation, which produced a profound use-dependent current attenuation not seen in the wild ...

Scientific Reports, 2011

Basic helix-loop-helix transcription factors Olig1 and Olig2 critically regulate oligodendrocyte ... more Basic helix-loop-helix transcription factors Olig1 and Olig2 critically regulate oligodendrocyte development. Initially identified as a downstream effector of Olig1, an oligodendrocyte-specific zinc finger transcription repressor, Zfp488, cooperates with Olig2 function. Although Zfp488 is required for oligodendrocyte precursor formation and differentiation during embryonic development, its role in oligodendrogenesis of adult neural progenitor cells is not known. In this study, we tested whether Zfp488 could promote an oligodendrogenic fate in adult subventricular zone (SVZ) neural stem/progenitor cells (NSPCs). Using a cuprizone-induced demyelination model in mice, we examined the effect of retrovirus-mediated Zfp488 overexpression in SVZ NSPCs. Our results showed that Zfp488 efficiently promoted the differentiation of the SVZ NSPCs into mature oligodendrocytes in vivo. After cuprizone-induced demyelination injury, Zfp488-transduced mice also showed significant restoration of motor function to levels comparable to control mice. Together, these findings identify a previously unreported role for Zfp488 in adult oligodendrogenesis and functional remyelination after injury.

Stem Cells, 2013

Pluripotent stem cells (PSCs) have been differentiated into oligodendroglial progenitor cells (OP... more Pluripotent stem cells (PSCs) have been differentiated into oligodendroglial progenitor cells (OPCs), providing promising cell replacement therapies for many central nervous system disorders. Studies from rodents have shown that brain OPCs express a variety of ion channels, and that a subset of brain OPCs express voltage-gated sodium channel (NaV), mediating the spiking properties of OPCs. However, it is unclear whether PSC-derived OPCs exhibit electrophysiological properties similar to brain OPCs and the role of NaV in the functional maturation of OPCs is unknown. Here, using a mouse embryonic stem cell (mESC) green fluorescent protein (GFP)-Olig2 knockin reporter line, we demonstrated that unlike brain OPCs, all the GFP+/Olig2+ mESC-derived OPCs (mESC-OPCs) did not express functional NaV and failed to generate spikes (hence termed “nonspiking mESC-OPCs”), while expressing the delayed rectifier and inactivating potassium currents. By ectopically expressing NaV1.2 α subunit via vira...

Science, 1992

N-type calcium channels are omega-conotoxin (omega-CgTx)-sensitive, voltage-dependent ion channel... more N-type calcium channels are omega-conotoxin (omega-CgTx)-sensitive, voltage-dependent ion channels involved in the control of neurotransmitter release from neurons. Multiple subtypes of voltage-dependent calcium channel complexes exist, and it is the alpha_1 subunit of the complex that forms the pore through which calcium enters the cell. The primary structures of human neuronal calcium channel alpha1B subunits were deduced by the characterization

Neuron, 1992

ABSTRACT The primary structures of human neuronal alpha 1, alpha 2, and beta subunits of a voltag... more ABSTRACT The primary structures of human neuronal alpha 1, alpha 2, and beta subunits of a voltage-dependent Ca2+ channel were deduced by characterizing cDNAs. The alpha 1 subunit (alpha 1D) directs the recombinant expression of a dihydropyridine-sensitive L-type Ca2+ channel when coexpressed with the beta (beta 2) and the alpha 2 (alpha 2b) subunits in Xenopus oocytes. The recombinant channel is also reversibly blocked by 10-15 microM omega-conotoxin. Expression of the alpha 1D subunit alone, or coexpression with the alpha 2b subunit, did not elicit functional Ca2+ channel activity. Thus, the beta 2 subunit appears to serve an obligatory function, whereas the alpha 2b subunit appears to play an accessory role that potentiates expression of the channel. The primary transcripts encoding the alpha 1D, alpha 2, and beta subunits are differentially processed. At least two forms of neuronal alpha 1D were identified. Different forms of alpha 2 and beta transcripts were also identified in CNS, skeletal muscle, and aorta tissues.

Journal of Neurochemistry, 2007

We adopted a genetic approach to test the importance of edited GluR2-free, Ca 2+-permeable, a-ami... more We adopted a genetic approach to test the importance of edited GluR2-free, Ca 2+-permeable, a-amino-3-hydroxy-5methyl-4-isoxazolepropionate (AMPA) receptors in the pathophysiology of experimental autoimmune encephalomyelitis, an inflammatory demyelinative disorder resembling multiple sclerosis. Initial studies showed that oligodendroglial lineage cells from mice lacking functional copies of the gene encoding the GluR3 AMPA receptor subunit (Gria3) had a diminished capacity to assemble edited GluR2-free AMPA receptors, and were resistant to excitotoxicity in vitro. Neurological deficits and spinal cord demyelination elicited by immunization with myelin oligodendrocyte glycoprotein peptide were substantially milder in these Gria3 mutant mice than in their wild-type littermates. These results support the hypothesis that oligodendroglial excitotoxicity mediated by AMPA receptors that do not contain edited GluR2 subunits contributes to demyelination in experimental autoimmune encephalomyelitis, and suggest that inhibiting these Ca 2+-permeable AMPA receptors would be therapeutic in multiple sclerosis.

Journal of Biological Chemistry, 2000

A new eukaryotic nutrient amino acid transporter has been cloned from an epithelium that is expos... more A new eukaryotic nutrient amino acid transporter has been cloned from an epithelium that is exposed to high voltages and alkaline pH. The full-length cDNA encoding this novel CAATCH1 (cation-anion-activated Amino acid transporter/channel) was isolated using a polymerase chain reaction-based strategy, and its expression product in Xenopus oocytes displayed a combination of several unique, unanticipated functional properties. CAATCH1 electrophysiological properties resembled those of Na ؉ ,Cl ؊-coupled neurotransmitter amine transporters, although CAATCH1 was cloned from a gut absorptive epithelium rather than from an excitable tissue. Amino acids such as L-proline, L-threonine, and L-methionine elicited complex current-voltage relationships in alkaline pH-dependent CAATCH1 that were reminiscent of the behavior of the dopamine, serotonin, and norepinephrine transporters (DAT, SERT, NET) in the presence of their substrates and pharmacological inhibitors such as cocaine or antidepressants. These I-V relationships indicated a combination of substrate-associated carrier current plus an independent CAATCH1associated leakage current that could be blocked by certain amino acids. However, unlike all structurally related proteins, CAATCH1 activity is absolutely independent of Cl ؊. Unlike related KAAT1, CAATCH1 possesses a methionine-inhibitable constitutive leakage current and is able to switch its narrow substrate selectivity, preferring threonine in the presence of K ؉ but preferring proline in the presence of Na ؉ .

Glia, 2008

Acid-sensing ion channels (ASICs) are widely expressed in neurons, where they serve in pain and m... more Acid-sensing ion channels (ASICs) are widely expressed in neurons, where they serve in pain and mechanical sensation, and contribute to learning and memory. Six ASIC subunit proteins form homoor heteromeric channel complexes with distinct physiological properties. Of such complexes, only monomeric ASIC1a channels are Ca 2+ permeable. Prior pharmacologic and genetic studies have shown that ASIC1a channel inactivation markedly diminishes CNS susceptibility to ischemic damage. Here, we characterize ASIC expression in oligodendrocyte lineage cells (OLC) by molecular, electrophysiological, calcium imaging, and immunofluorescence techniques. ASIC1a, ASIC2a, and ASIC4 mRNAs were expressed in cultured rat OLC, with steady-state levels of each of these mRNAs several-fold higher in oligodendroglial progenitors than in mature oligodendroglia. ASIC transcripts were also detected in brain white matter, and ASIC1a protein expression was detected in white matter oligodendroglia. Inactivating, proton-gated, amiloride-sensitive OLC currents were detected by whole-cell voltage clamp. These currents showed profound tachyphylaxis with slow recovery, and were predominantly blocked by psalmotoxin, indicating that homomeric ASIC1a comprised a large fraction of functional ASIC in the cultured OLC. ASIC activation substantially depolarized OLC plasma membrane in current clamp studies, and elicited transient elevations in intracellular Ca 2+ in imaging studies. Thus, OLC ASIC1a channels provide a means by which an acid shift in CNS extracellular pH, by diminishing plasma membrane potential and increasing Ca 2+ permeability, can activate OLC signaling pathways, and may contribute to OLC vulnerability to CNS ischemia.