Elucidating the Molecular Basis of Action of a Classic Drug: Guanidine Compounds As Inhibitors of Voltage-Gated Potassium Channels

Abstract

Guanidine and its alkyl analogs stimulate the neuromuscular junction presynaptically by inhibiting voltage-gated potassium (Kv) channels, leading to enhanced release of acetylcholine in the synaptic cleft. This stimulatory effect of guanidine underlies its use in the therapy for the neuromuscular diseases myasthenic syndrome of Lambert-Eaton and botulism. The therapeutic use of guanidine is limited, however, because of side effects that accompany its administration. Therefore, the design of guanidine analogs with improved therapeutic indices is desirable. Progress toward this goal is hindered by the lack of knowledge of the mechanism by which these molecules inhibit Kv channels. Here we examine an array of possible mechanisms, including charge screening, disruption of the proteinlipid interfaces, direct interaction with the voltage sensors, and pore-binding. Our results demonstrate that guanidines bind within the intracellular pore of the channel and perturb a hydrophobic subunit interface to stabilize a closed state of the channel. This mechanism provides a foundation for the design of guanidine analogs for the therapeutic intervention of neuromuscular diseases.

Voltage-Sensing Domain of Voltage-Gated Proton Channel Hv1 Shares Mechanism of Block with Pore Domains

“…The strong sensitivity of Hv1 to intracellular 2GBI and the lack of sensitivity to extracellular 2GBI (measured over the same time scale and concentration range) imply that the binding site on the channel is directly accessible only from the intracellular side of the membrane. However, slow membrane crossing by guanidine derivatives has been previously observed (Kalia and Swartz, 2011). So, we cannot exclude that longer treatments with extracellular 2GBI than the ones tested here could result in Hv1 inhibition.…”

Inhibition of Neuronal Degenerin/Epithelial Na+ Channels by the Multiple Sclerosis Drug 4-Aminopyridine

“…The importance of this with respect to actions on Deg/ENaC channels is as yet unknown; however, it is recognized that ionization of 4-AP is critical to its blockade of Kv channels (3,6,45). Similarly, the positive charge of the guanidinium cation is critical to blockade of Deg/ENaC channels by amiloride (46).…”

Efficacy of Antitoxin Therapy in Treating Patients With Foodborne Botulism: A Systematic Review and Meta-analysis of Cases, 1923–2016

“…These measures have been credited with reducing botulism mortality in the United States from >60% in the early 20th century to <5% at present [5]. Additionally, other targeted treatments have been attempted to ameliorate the effects of botulism, such as cathartics and enemas to clear toxin from the gastrointestinal tract, and guanidine and 3,4-diaminopuridine to stimulate acetylcholine release [6].…”