Abstract
The voltage-gated K(+) (Kv) channel blocker 4-aminopyridine (4-AP) is used to target symptoms of the neuroinflammatory disease multiple sclerosis (MS). By blocking Kv channels, 4-AP facilitates action potential conduction and neurotransmitter release in presynaptic neurons, lessening the effects of demyelination. Because they conduct inward Na(+) and Ca(2+) currents that contribute to axonal degeneration in response to inflammatory conditions, acid-sensing ion channels (ASICs) contribute to the pathology of MS. Consequently, ASICs are emerging as disease-modifying targets in MS. Surprisingly, as first demonstrated here, 4-AP inhibits neuronal degenerin/epithelial Na(+) (Deg/ENaC) channels, including ASIC and BLINaC. This effect is specific for 4-AP compared with its heterocyclic base, pyridine, and the related derivative, 4-methylpyridine; and akin to the actions of 4-AP on the structurally unrelated Kv channels, dose- and voltage-dependent. 4-AP has differential actions on distinct ASICs, strongly inhibiting ASIC1a channels expressed in central neurons but being without effect on ASIC3, which is enriched in peripheral sensory neurons. The voltage dependence of the 4-AP block and the single binding site for this inhibitor are consistent with 4-AP binding in the pore of Deg/ENaC channels as it does Kv channels, suggesting a similar mechanism of inhibition in these two classes of channels. These findings argue that effects on both Kv and Deg/ENaC channels should be considered when evaluating the actions of 4-AP. Importantly, the current results are consistent with 4-AP influencing the symptoms of MS as well as the course of the disease because of inhibitory actions on Kv and ASIC channels, respectively.
Highlights
Ized by demyelination of neurons [1,2,3,4]
The current results demonstrate that 4-AP is an inhibitor of the Deg/ENaC channels expressed in neurons
The representative macroscopic currents conducted by homomeric ASIC1a, 1b, 2a, and 3, and heteromeric ASIC1a/2a and ASIC1a/3 in voltage-clamped Chinese hamster ovary (CHO) cells as shown in Fig. 3a, and the associated summary graph in 3b demonstrate that 4-AP has isoform-specific effects on the Deg/ ENaC channels expressed in neurons
Summary
Materials—All chemicals and materials were purchased from Sigma and Calbiochem unless noted otherwise. Neurons were clamped to Ϫ60 mV with PPK1 currents evoked using a standard protocol, as described previously by us [31], entailing relief from amiloride blockade subsequent to an activating acid (pH 4.5) pre-prepulse For these experiments, the extracellular bath solution contained 140 mM NaCl, 5 mM KCl, 1 mM CaCl2, 10 mM D-glucose, 10 mM HEPES, and 10 mM MES (pH was adjusted with HCl before each experiment). Whole cell macroscopic current recordings of ASIC expressed in CHO cells were performed under voltage-clamp conditions (Vm ϭ Ϫ10 mV) using standard methods [34] In these experiments, ASIC currents were evoked by rapid solution exchange from control (7.6) to acidic (5.0) pH. Single-channel current recordings of recombinant BLINaC expressed in CHO cells were acquired in the excised, outsideout patch configuration under voltage clamp conditions using standard methods [24, 40]. Where percentage inhibition and g/gmax are the blocked fraction of current and nonblocked fraction of conductance, respectively, in the presence of blocker at concentration [X]; IC50 is the half-maximal concentration of blocker; and n is the Hill coefficient
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
