Document Type


Publication Date



This article is the author’s final published version in Journal of Biological Chemistry, Volume 296, January 2021, Article number 100302.

The published version is available at Copyright © Ojala et al.


3,4-Diaminopyridine (3,4-DAP) increases transmitter release from neuromuscular junctions (NMJs), and low doses of 3,4-DAP (estimated to reach ∼1 μM in serum) are the Food and Drug Administration (FDA)-Approved treatment for neuro muscular weakness caused by Lambert-Eaton myasthenic syn drome. Canonically, 3,4-DAP is thought to block voltage-gated potassium (Kv) channels, resulting in prolongation of the pre synaptic action potential (AP). However, recent reports have shown that low millimolar concentrations of 3,4-DAP have an off-Target agonist effect on the Cav1 subtype ("L-Type") of voltage-gated calcium (Cav) channels and have speculated that this agonist effect might contribute to 3,4-DAP effects on transmitter release at the NMJ. To address 3,4-DAPs mecha nism(s) of action, we first used the patch-clamp electrophysi ology to characterize the concentration-dependent block of 3,4-DAP on the predominant presynaptic Kv channel subtypes found at the mammalian NMJ (Kv3.3 and Kv3.4). We identified a previously unreported high-Affinity (1-10 μM) partial antag onist effect of 3,4-DAP in addition to the well-known low-Af finity (0.1-1 mM) antagonist activity. We also showed that 1.5-μM DAP had no effects on Cav1.2 or Cav2.1 current. Next, we used voltage imaging to show that 1.5-or 100-μM 3,4-DAP broadened the AP waveform in a dose-dependent manner, in dependent of Cav1 calcium channels. Finally, we demonstrated that 1.5-or 100-μM 3,4-DAP augmented transmitter release in a dose-dependent manner and this effect was also independent of Cav1 channels. From these results, we conclude that low micromolar concentrations of 3,4-DAP act solely on Kv chan nels to mediate AP broadening and enhance transmitter release at the NMJ.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.



Included in

Neurosciences Commons