Saclofen is a competitive

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

for the GABA_B receptor. This drug is an analogue of the GABA_B agonist

baclofen Baclofen, sold under the brand name Lioresal among others, is a medication used to treat muscle spasticity such as from a spinal cord injury or multiple sclerosis. It may also be used for hiccups and muscle spasms near the end of life. It is ta ...

. The GABA_B receptor is heptahelical receptor, expressed as an obligate heterodimer, which couples to the Gi/o class of heterotrimeric G-proteins. The action of saclofen on the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

is understandably modest, because G-proteins rely on an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

cascade Cascade, Cascades or Cascading may refer to: Science and technology Science *Cascade waterfalls, or series of waterfalls * Cascade, the CRISPR-associated complex for antiviral defense (a protein complex) * Cascade (grape), a type of fruit * Bioc ...

to alter cell behavior while

ionotropic Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in res ...

receptors immediately change the ionic permeability of the neuronal plasma membrane, thus changing its firing patterns. These particular receptors, presynaptically inhibit N- and P/Q-

voltage-gated calcium channels Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (''e.g.'', muscle, glial cells, neurons, etc.) with a permeabili ...

(VGCCs) via a direct interaction of the dissociated beta gamma subunit of the g-protein with the intracellular loop between the 1st and 2nd domain of the VGCC's alpha-subunit; postsynaptically, these potentiate K_ir currents. Both result in inhibitory effects. However, in animal experiments, saclofen is paradoxically observed to have an

antiepileptic Anticonvulsants (also known as antiepileptic drugs or recently as antiseizure drugs) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of b ...

effect. This is probably because GABA_B effect is coupled to excitation in the thalamo-cortical circuits — K_ir coupling via Gβγ subunits is so strong that it lowers the threshold for T-type Ca²⁺ channel opening enough to elicit their opening, and thus an excitation in this circuit. Since thalamo-cortical circuit overfiring is seen in types of epilepsy involving

absence seizure Absence seizures are one of several kinds of generalized seizures. These seizures are sometimes referred to as petit mal seizures (from the French for "little illness", a term dated in the late 18th century). Absence seizures are characterized by ...

s (

ethosuximide Ethosuximide, sold under the brand name Zarontin among others, is a medication used to treat absence seizures. It may be used by itself or with other antiseizure medications such as valproic acid. Ethosuximide is taken by mouth. Ethosuximide ...

, a T-type Ca²⁺ channel blocker, is used in the treatment of this), the unexpected antiepileptic effects of saclofen may thus be explained (unexpected as the GABA receptors are inhibitory, and antagonizing them should lead to hyperactivity of the affected

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s). Possible

therapeutic A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis. As a rule, each therapy has indications and contraindications. There are many different ...

uses of saclofen are currently being researched. Saclofen has two

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

ic forms. The (''R'')-stereoisomer is the one that binds to the GABA_B receptor, whereas the (''S'')-stereoisomer does not.

References

{{GABAergics Chloroarenes GABAB receptor antagonists Sulfonic acids