Chemical and biophysical characterization of novel potassium channel blocker 3-fluoro-5-methylpyridin-4-amine.

4-aminopyridine (4AP) is a potassium (K) channel blocker used clinically to improve walking in people with multiple sclerosis (MS). 4AP binds to exposed K channels in demyelinated axons, reducing the leakage of intracellular K and enhancing impulse conduction. Multiple derivatives of 4AP capable of blocking K channels have been reported including three radiolabeled with positron emitting isotopes for imaging demyelinated lesions using positron emission tomography (PET).

Electro-steric opening of the CLC-2 chloride channel gate.

The widely expressed two-pore homodimeric inward rectifier CLC-2 chloride channel regulates transepithelial chloride transport, extracellular chloride homeostasis, and neuronal excitability. Each pore is independently gated at hyperpolarized voltages by a conserved pore glutamate. Presumably, exiting chloride ions push glutamate outwardly while external protonation stabilizes it.

Structure-activity relationship studies of four novel 4-aminopyridine K channel blockers.

4-Aminopyridine (4AP) is a specific blocker of voltage-gated potassium channels (K1 family) clinically approved for the symptomatic treatment of patients with multiple sclerosis (MS). It has recently been shown that [F]3F4AP, a radiofluorinated analog of 4AP, also binds to K1 channels and can be used as a PET tracer for the detection of demyelinated lesions in rodent models of MS. Here, we investigate four novel 4AP derivatives containing methyl (-CH), methoxy (-OCH) as well as trifluoromethyl (-CF) in the 2 and 3 position as potential candidates for PET imaging and/or therapy.

Development of a PET radioligand for potassium channels to image CNS demyelination.

Central nervous system (CNS) demyelination represents the pathological hallmark of multiple sclerosis (MS) and contributes to other neurological conditions. Quantitative and specific imaging of demyelination would thus provide critical clinical insight. Here, we investigated the possibility of targeting axonal potassium channels to image demyelination by positron emission tomography (PET).

LRET Determination of Molecular Distances during pH Gating of the Mammalian Inward Rectifier Kir1.1b.

Gating of the mammalian inward rectifier Kir1.1 at the helix bundle crossing (HBC) by intracellular pH is believed to be mediated by conformational changes in the C-terminal domain (CTD). However, the exact motion of the CTD during Kir gating remains controversial.

β1-subunit-induced structural rearrangements of the Ca2+- and voltage-activated K+ (BK) channel.

Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels are involved in a large variety of physiological processes. Regulatory β-subunits are one of the mechanisms responsible for creating BK channel diversity fundamental to the adequate function of many tissues. However, little is known about the structure of its voltage sensor domain.

A structural rearrangement of the Na+/K+-ATPase traps ouabain within the external ion permeation pathway.

With the use of the energy of ATP hydrolysis, the Na+/K+-ATPase is able to transport across the cell membrane Na+ and K+ against their electrochemical gradients. The enzyme is strongly inhibited by ouabain and its derivatives, some that are therapeutically used for patients with heart failure (cardiotonic steroids). Using lanthanide resonance energy transfer, we trace here the conformational changes occurring on the external side of functional Na+/K+-ATPases induced by the binding of ouabain.

Sequential interaction of chloride and proton ions with the fast gate steer the voltage-dependent gating in ClC-2 chloride channels.

The interaction of either H(+) or Cl(-) ions with the fast gate is the major source of voltage (V(m)) dependence in ClC Cl(-) channels. However, the mechanism by which these ions confer V(m) dependence to the ClC-2 Cl(-) channel remains unclear. By determining the V(m) dependence of normalized conductance (G(norm)(V(m))), an index of open probability, ClC-2 gating was studied at different [H(+)](i), [H(+)](o) and [Cl(-)](i).

Ouabain binding site in a functioning Na+/K+ ATPase.

The Na(+)/K(+) ATPase is an almost ubiquitous integral membrane protein within the animal kingdom. It is also the selective target for cardiotonic derivatives, widely prescribed inhibitors for patients with heart failure. Functional studies revealed that ouabain-sensitive residues distributed widely throughout the primary sequence of the protein.

Simulating complex ion channel kinetics with IonChannelLab.

In silico simulation based on Markov chains is a powerful way to describe and predict the activity of many transport proteins including ion channels. However, modeling and simulation using realistic models of voltage- or ligand-gated ion channels exposed to a wide range of experimental conditions require building complex kinetic schemes and solving complicated differential equations. To circumvent these problems, we developed IonChannelLab a software tool that includes a user-friendly Graphical User Interface and a simulation library.

Permeant anions contribute to voltage dependence of ClC-2 chloride channel by interacting with the protopore gate.

It has been shown that the voltage (V(m)) dependence of ClC Cl(-) channels is conferred by interaction of the protopore gate with H(+) ions. However, in this paper we present evidence which indicates that permeant Cl(-) ions contribute to V(m)-dependent gating of the broadly distributed ClC-2 Cl() channel. The apparent open probability (P(A)) of ClC-2 was enhanced either by changing the [Cl(-)](i) from 10 to 200 mM or by keeping the [Cl(-)](i) low (10 mM) and then raising [Cl(-)](o) from 10 to 140 mM.