NS309 is the most potent positive gating modulator for intermediate-conductance Ca2+-activated K+ channel KCa3.1, with an EC50 of 75nmol/L[1]. NS309 was binding within the interface between calmodulin's N-lobe and the S4-S5 linker to exhibit the agonist activity, and NS309 forms hydrogen bonds between the NS309’s carbonyl and residues N201 and R287[2]. NS309 functions as a pharmacological agent to enhance the activity of both small and intermediate conductance calcium-activated potassium channels[3].
In vitro, NS309 can stimulate changes in the cell's ions[4]. The exposure of diabetes-derived human coronary endothelial cells to 10μmol/L NS309 for 15 minutes led to a significant rise in total K+ current while simultaneously causing cell hyperpolarization[4]. Human red cells displayed near full dehydration after 2 hours when treated with NS309 at 100μmol/L in a medium containing only 4μmol/L external Ca2+[5]. The administration of NS309 (10μmol/L for 2 minutes) led to a significant rise in whole cell small conductance Ca2+-activated K+ currents while causing hyperpolarization of the resting membrane potential in detrusor smooth muscle cell of rats[6].
In vivo, NS309 has neuroprotective effects[7]. Intraperitoneal injection of 2mg/kg NS309 for 10 days significantly reduced brain edema and neuronal apoptosis in rats with traumatic brain injury, and decreased the number of neutrophils, lymphocytes and microglia[7]. The administration of NS309 through the intrathecal route at concentrations of 100μmol/L for 30 minutes reduced complete Freund adjuvant (CFA)-induced mechanical hypersensitivity in the rat model of inflammatory pain[8].
References:
[1]Nasburg J, Wulff H, Shim H, et al. Exploring the binding site and mechanism of action of NS309, a superagonistic positive gating modulator for the calcium-activated potassium channel KCa3. 1[J]. Biophysical Journal, 2024, 123(3): 261a-262a.
[2]Nasburg J A. Mapping the binding site of NS309, a superagonistic positive gating modulator for the calcium-activated potassium channel KCa3. 1[J]. Biophysical Journal, 2023, 122(3): 252a.
[3]Nasburg J A, Rouen K C, Dietrich C J, et al. NS309 Functions as a Superagonist for the Calcium-Activated Potassium Channel KCa3. 1[J]. Molecular Pharmacology, 2025: 100018.
[4]Liu Y, Xie A, Singh A K, et al. Inactivation of endothelial small/intermediate conductance of calcium‐activated potassium channels contributes to coronary arteriolar dysfunction in diabetic patients[J]. Journal of the american heart association, 2015, 4(8): e002062.
[5]Seear R V, Lew V L. IKCa agonist (NS309)-elicited all-or-none dehydration response of human red blood cells is cell-age dependent[J]. Cell Calcium, 2011, 50(5): 444-448.
[6]Parajuli S P, Hristov K L, Soder R P, et al. NS309 decreases rat detrusor smooth muscle membrane potential and phasic contractions by activating SK3 channels[J]. British journal of pharmacology, 2013, 168(7): 1611-1625.
[7]Chen T, Zhu J, Hang C H, et al. The potassium SK channel activator NS309 protects against experimental traumatic brain injury through anti-inflammatory and immunomodulatory mechanisms[J]. Frontiers in pharmacology, 2019, 10: 1432.
[8]Hipólito L, Fakira A K, Cabañero D, et al. In vivo activation of the SK channel in the spinal cord reduces the NMDA receptor antagonist dose needed to produce antinociception in an inflammatory pain model[J]. Pain, 2015, 156(5): 849-858.