NS 1619

The mitochondrial Ca2+-activated K+ channel activator, NS 1619 inhibits L-type Ca2+ channels in rat ventricular myocytes.[Pubmed:17698036]

Biochem Biophys Res Commun. 2007 Oct 12;362(1):31-36.

We examined the effects of the mitochondrial Ca(2+)-activated K(+) (mitoBK(Ca)) channel activator NS 1619 on L-type Ca(2+) channels in rat ventricular myocytes. NS 1619 inhibited the Ca(2+) current in a dose-dependent manner. NS 1619 shifted the activation curve to more positive potentials, but did not have a significant effect on the inactivation curve. Pretreatment with inhibitors of membrane BK(Ca) channel, mitoBK(Ca) channel, protein kinase C, protein kinase A, and protein kinase G had little effect on the Ca(2+) current and did not alter the inhibitory effect of NS 1619 significantly. The application of additional NS 1619 in the presence of isoproterenol, a selective beta-adrenoreceptor agonist, reduced the Ca(2+) current to approximately the same level as a single application of NS 1619. In conclusion, our results suggest that NS 1619 inhibits the Ca(2+) current independent of the mitoBK(Ca) channel and protein kinases. Since NS 1619 is widely used to study mitoBK(Ca) channel function, it is essential to verify these unexpected effects of NS 1619 before experimental data can be interpreted accurately.

Functional contribution of the endothelial component to the vasorelaxing effect of resveratrol and NS 1619, activators of the large-conductance calcium-activated potassium channels.[Pubmed:17203288]

Naunyn Schmiedebergs Arch Pharmacol. 2007 Mar;375(1):73-80.

Large-conductance calcium-activated potassium channels (BK) of smooth muscle play a role in the relevant modulation of vascular tone, due to their calcium- and voltage-dependent mechanisms of activation. A potential role of endothelial BK channels has also been suggested by approaches on endothelial cell cultures. However, no functional study, aimed at evaluating the contribution of endothelial BK channels to the effect of BK-openers, has been reported. Resveratrol and NS 1619, BK-openers, have been tested on endothelium-intact and -denuded aortic rings. Furthermore, the effects of high depolarisation of potassium channel blockers TEA (Tetraethylammonium), 4-AP ( 4-Aminopyridine) and IbTX (Iberiotoxin) and of inhibitors of NO-pathway (L-NAME and ODQ) have been evaluated. The presence of endothelium increased the vasorelaxing potency of BK-openers. This potentiation was eliminated by L-NAME and ODQ. TEA, 4-AP, IbTX and high depolarisation had modest or no antagonist influence on resveratrol in endothelium-denuded aortic rings. The effects of NS 1619 on endothelium-denuded aortic rings were not affected by IbTX, and were modestly antagonised by TEA, 4-AP and high depolarisation. In intact endothelium vessels, TEA, IbTX and 4-AP antagonised the vasorelaxing effect of the two BK-activators. A BK-mediated release of endothelial NO seems a very important factor, determining a strong influence on vasodilator profile of BK-openers. Therefore, an eventual therapy with a BK-opener could promote a series of cardiovascular impacts not confined to the only direct vasorelaxing effects, but also due to a significant contribution of endothelial NO.

Inhibition of guinea pig detrusor contraction by NS-1619 is associated with activation of BKCa and inhibition of calcium currents.[Pubmed:9399993]

J Pharmacol Exp Ther. 1997 Dec;283(3):1193-200.

The effects of NS-1619 on bladder contractile function and on transmembrane currents were evaluated in vitro on isolated guinea pig detrusor strips and isolated detrusor myocytes, respectively. In the isolated bladder strip, NS-1619 inhibited KCl-induced contractions in a concentration-dependent manner (IC50 = 12.2 +/- 3. 2 microM). Isolated detrusor myocytes were quiescent and had resting membrane potentials that averaged -45.3 +/- 2.7 mV. With patch-clamp techniques we demonstrated that exposure to 10 to 100 microM NS-1619 increased an iberiotoxin-sensitive current consistent with the activation of the large conductance calcium-dependent potassium channel (BKCa). Single-channel analysis confirmed that NS-1619 increased the open probability of BKCa channels. NS-1619 also appeared to decrease inward calcium current (ICa). After exposure to 30 microM NS-1619, peak current amplitude significantly decreased by approximately 50%. Analysis of the current voltage relationship revealed a significant decrease in maximal conductance from 10.5 +/- 4 to 6.2 +/- 3 nS. The voltage dependence of calcium current activation and inactivation was well fit by a Boltzmann relationship. Besides the decrease in conductance, there was a small, but significant shift in the half-inactivation voltage, which suggests that NS-1619 preferentially blocks the open state of the channel. Steady-state (window) calcium current was also decreased. Analysis of the theoretical window current revealed a 71% decrease in this noninactivating current. These data indicate that NS-1619 inhibits detrusor smooth muscle contraction in a concentration-dependent manner and that the underlying mechanism of action for this effect involves inhibition of calcium current, and may also include activation of the BKCa channel. Compounds with this profile may be useful in the treatment of bladder instability.

BK channel activation by NS-1619 is partially mediated by intracellular Ca2+ release in smooth muscle cells of porcine coronary artery.[Pubmed:11181423]

Br J Pharmacol. 2001 Feb;132(4):828-34.

1. Effects of NS-1619, an opener of large conductance Ca2+-activated K+ (BK) channel, on intracellular Ca2+ concentration ([Ca2+]i) and membrane potential were examined in single myocytes freshly isolated from porcine coronary artery. 2. Under current clamp mode, the application of 1-30 microM NS-1619 hyperpolarized the membrane in concentration-dependent manner. The NS-1619-induced hyperpolarization was abolished by the presence of 100 nM iberiotoxin. 3. Application of 1-10 microM NS-1619 hyperpolarized the membrane by approximately 6 mV or less but did not change significantly the [Ca2+]i. When membrane hyperpolarization of 12 mV or so was caused by 30 microM NS-1619, [Ca2+]i was unexpectedly increased by approximately 200 nM. This increase in [Ca2+]i and the concomitant outward current activation were also observed under voltage-clamp at holding potential of -40 mV. 4. The increase in [Ca2+]i by 30 microM NS-1619 occurred mainly in peripheral regions than in the centre of the myocytes. The removal of extracellular Ca2+ affected neither the membrane hyperpolarization nor the increase in [Ca2+]i. 5. In the presence of 10 mM caffeine and 10 microM ryanodine, the increase in [Ca2+]i by 30 microM NS-1619 was not observed and the membrane hyperpolarization was reduced to approximately 67% of the control. 6. These results indicate that the opening of BK channels by NS-1619 at 30 microM, which is the most frequently used concentration of this agent, is partly due to Ca2+ release from caffeine/ryanodine-sensitive intracellular storage sites but is mainly due to the direct activation of the channels.

Large-conductance K+ channel openers NS1619 and NS004 as inhibitors of mitochondrial function in glioma cells.[Pubmed:12781334]

Biochem Pharmacol. 2003 Jun 1;65(11):1827-34.

Recently, it has been reported that large-conductance Ca(2+)-activated potassium channels, also known as BK(Ca)-type potassium channels, are present in the inner mitochondrial membrane of the human glioma LN229 cell line. Hence, in the present study, we have investigated whether BK(Ca)-channel openers (BK(Ca)COs), such as the benzimidazolone derivatives NS004 (5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidazole-2-on e) and NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzi midazol-2-one), affect the functioning of LN229 glioma cell mitochondria in situ. We examined the effect of BK(Ca)COs on mitochondrial membrane potential, mitochondrial respiration and plasma membrane potassium current in human glioma cell line LN229. We found that BK(Ca)COs decrease the mitochondrial membrane potential with an EC(50) value of 3.6+/-0.4 microM for NS1619 and 5.4+/-0.8 microM for NS004. This mitochondrial depolarization was accompanied by an inhibition of the mitochondrial respiratory chain. Both BK(Ca)COs induced whole-cell potassium current blocked by charybdotoxin, as measured by the patch-clamp technique. The BK(Ca)COs had no effect on membrane bilayer conductance. Moreover, the inhibition of mitochondrial function by NS004 and NS1619 was without effect on cell survival, as measured by lactate dehydrogenase release from the cells.

Selective activation of Ca(2+)-dependent K+ channels by novel benzimidazolone.[Pubmed:8137869]

Eur J Pharmacol. 1994 Jan 4;251(1):53-9.

Activators and blockers of specific ion channels are important pharmacological tools for characterizing ion channels and their influence on cell function. The large-conductance Ca(2+)-dependent K+ channel (BK channel) is blocked by peptides such as charybdotoxin and iberiotoxin, but no selective activator of the channel has been described. Here we report single-channel and whole-cell patch-clamp experiments on the specific activation of BK channels in aortic smooth muscle cells with a new heterocyclic molecule, NS 1619 (1-(2'-hydroxy-5'-trifluoromethylphenyl)-5-trifluoromethyl- 2(3H)benzimidazolone). The effect of NS 1619 on the BK channel was dose-dependent, resulting in a shift of the activation curve by up to -50 mV towards negative membrane potentials. The effect was fully reversible and was antagonized by charybdotoxin as well as by tetraethylammonium ions. The compound hyperpolarized the smooth muscle cells. NS 1619 is a selective and new type of K+ channel activator, which may significantly modulate cell excitability.