Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients.

Introduction: Individual mutations in the SCN5A-encoding cardiac sodium channel α-subunit usually cause a single cardiac arrhythmia disorder, some cause mixed biophysical or clinical phenotypes. Here we report an infant, female patient harboring a N406K mutation in SCN5A with a marked and mixed biophysical phenotype and assess pathogenic mechanisms.

Methods And Results: A patient suffered from recurrent seizures during sleep and torsades de pointes with a QTc of 530 ms.

Arrhythmogenic Biophysical Phenotype for SCN5A Mutation S1787N Depends upon Splice Variant Background and Intracellular Acidosis.

Background: SCN5A is a susceptibility gene for type 3 long QT syndrome, Brugada syndrome, and sudden infant death syndrome. INa dysfunction from mutated SCN5A can depend upon the splice variant background in which it is expressed and also upon environmental factors such as acidosis. S1787N was reported previously as a LQT3-associated mutation and has also been observed in 1 of 295 healthy white controls.

Regulation of L-type calcium channel by phospholemman in cardiac myocytes.

We evaluated whether phospholemman (PLM) regulates L-type Ca(2+) current (ICa) in mouse ventricular myocytes. Expression of α1-subunit of L-type Ca(2+) channels between wild-type (WT) and PLM knockout (KO) hearts was similar. Compared to WT myocytes, peak ICa (at -10 mV) from KO myocytes was ~41% larger, the inactivation time constant (τ(inact)) of ICa was ~39% longer, but deactivation time constant (τ(deact)) was similar.

Amino acid substitutions in the pore affect the anomalous mole fraction effect of CaV1.2 channels.

The anomalous mole fraction effect (AMFE) is an important indicator of ion-ion interactions in the pore of voltage-gated Ca2+ channels (VGCCs). The residues at position 1144 that differ in several classes of VGCCs are important to the permeation of the pore. Phe-1144 (F, CaV1) was substituted with glycine (G, CaV2) and lysine (K, CaV3) and the effects of mutation on the voltage and concentration dependency of AMFE were observed.

Domain III regulates N-type (CaV2.2) calcium channel closing kinetics.

Ca(V)2.2 (N-type) and Ca(V)1.2 (L-type) calcium channels gate differently in response to membrane depolarization, which is critical to the unique physiological functions mediated by these channels.

Constitutive overexpression of phosphomimetic phospholemman S68E mutant results in arrhythmias, early mortality, and heart failure: potential involvement of Na+/Ca2+ exchanger.

Expression and activity of cardiac Na(+)/Ca(2+) exchanger (NCX1) are altered in many disease states. We engineered mice in which the phosphomimetic phospholemman S68E mutant (inhibits NCX1 but not Na(+)-K(+)-ATPase) was constitutively overexpressed in a cardiac-specific manner (conS68E). At 4-6 wk, conS68E mice exhibited severe bradycardia, ventricular arrhythmias, increased left ventricular (LV) mass, decreased cardiac output (CO), and ∼50% mortality compared with wild-type (WT) littermates.

Genetic variants and monoallelic expression of surfactant protein-D in inflammatory bowel disease.

Surfactant protein-D (SP-D) is expressed on mucosal surfaces and functions in the innate immune response to microorganisms. We studied the genetic association of the two nonsynonymous SP-D single nucleotide polymorphisms (SNPs) rs721917 and rs2243639 in 256 inflammatory bowel disease (IBD) cases (123 CD and 133 UC) and 376 unrelated healthy individuals from an IBD population from Central Pennsylvania. Case-control analysis revealed a significant association of rs2243639 with susceptibility to Crohn's disease (CD) (p= 0.

Amino acid substitutions in the FXYD motif enhance phospholemman-induced modulation of cardiac L-type calcium channels.

We have found that phospholemman (PLM) associates with and modulates the gating of cardiac L-type calcium channels (Wang et al., Biophys J 98: 1149-1159, 2010). The short 17 amino acid extracellular NH(2)-terminal domain of PLM contains a highly conserved PFTYD sequence that defines it as a member of the FXYD family of ion transport regulators.

Phospholemman modulates the gating of cardiac L-type calcium channels.

Ca(2+) entry through L-type calcium channels (Ca(V)1.2) is critical in shaping the cardiac action potential and initiating cardiac contraction. Modulation of Ca(V)1.

A single amino acid change in Ca(v)1.2 channels eliminates the permeation and gating differences between Ca(2+) and Ba(2+).

Glutamate scanning mutagenesis was used to assess the role of the calcicludine binding segment in regulating channel permeation and gating using both Ca(2+) and Ba(2+) as charge carriers. As expected, wild-type Ca(V)1.2 channels had a Ba(2+) conductance ~2x that in Ca(2+) (G(Ba)/G(Ca) = 2) and activation was ~10 mV more positive in Ca(2+) vs.

Roscovitine binds to novel L-channel (CaV1.2) sites that separately affect activation and inactivation.

L-type (Ca(V)1.2) calcium channel antagonists play an important role in the treatment of cardiovascular disease. (R)-Roscovitine, a trisubstituted purine, has been shown to inhibit L-currents by slowing activation and enhancing inactivation.

TRPA1 in mast cell activation-induced long-lasting mechanical hypersensitivity of vagal afferent C-fibers in guinea pig esophagus.

Sensitization of esophageal sensory afferents by inflammatory mediators plays an important role in esophageal nociception. We have shown esophageal mast cell activation induces long-lasting mechanical hypersensitivity in vagal nodose C-fibers. However, the roles of mast cell mediators and downstream ion channels in this process are unclear.

The Timothy syndrome mutation of cardiac CaV1.2 (L-type) channels: multiple altered gating mechanisms and pharmacological restoration of inactivation.

Timothy syndrome (TS) is a multiorgan dysfunction caused by a Gly to Arg substitution at position 406 (G406R) of the human CaV1.2 (L-type) channel. The TS phenotype includes severe arrhythmias that are thought to be triggered by impaired open-state voltage-dependent inactivation (OSvdI).

Calcicludine binding to the outer pore of L-type calcium channels is allosterically coupled to dihydropyridine binding.

How dihydropyridines modulate L-type voltage-gated Ca2+ channels is not known. Dihydropyridines bind cooperatively with Ca2+ binding to the selectivity filter, suggesting that they alter channel activity by promoting structural rearrangements in the pore. We used radioligand binding and patch-clamp electrophysiology to demonstrate that calcicludine, a toxin from the venom of the green mamba snake, binds in the outer vestibule of the pore and, like Ca2+, is a positive modulator of dihydropyridine binding.

Allosteric interactions required for high-affinity binding of dihydropyridine antagonists to Ca(V)1.1 Channels are modulated by calcium in the pore.

Dihydropyridines (DHPs) are an important class of drugs, used extensively in the treatment of angina pectoris, hypertension, and arrhythmia. The molecular mechanism by which DHPs modulate Ca(2+) channel function is not known in detail. We have found that DHP binding is allosterically coupled to Ca(2+) binding to the selectivity filter of the skeletal muscle Ca(2+) channel Ca(V)1.

Regulation of the transient receptor potential channel TRPM2 by the Ca2+ sensor calmodulin.

TRPM2, a member of the transient receptor potential (TRP) superfamily, is a Ca(2+)-permeable channel activated by oxidative stress or tumor necrosis factoralpha involved in susceptibility to cell death. TRPM2 activation is dependent on the level of intracellular Ca(2+). We explored whether calmodulin (CaM) is the Ca(2+) sensor for TRPM2.

Amino acid substitutions in the pore of the Ca(V)1.2 calcium channel reduce barium currents without affecting calcium currents.

Ba(2+) currents through Ca(V)1.2 Ca(2+) channels are typically twice as large as Ca(2+) currents. Replacing Phe-1144 in the pore-loop of domain III with glycine and lysine, and Tyr-1152 with lysine, reduces whole-cell G(Ba)/G(Ca) from 2.