Na+/Ca2+ exchanger (NCX) (IC50 = 100 nM)

Small conductance Ca2+-activated K2+ channels in neurons and heterologously generated K2+ channels are inhibited by benamil hydrochloride (benzylamiloride hydrochloride) [4].

After receiving Benzamil hydrochloride treatment (0.7 mg/kg/day; sc), stroke-prone spontaneously hypertensive rats (SHRSP) lived an average of 16.1 weeks [5].

Small conductance Ca2+-activated K+ (SK) channels are expressed throughout the soma and dendrites of pyramidal neurons in the neocortex and hippocampal formation, where they participate in the local regulation of membrane excitability and synaptic signals. Through their inter-play with Ca2+ channels, SK channels regulate Ca2+ influx triggered by back-propagating action potentials in dendrites. Inhibition of SK channels affects both the amplitude and duration of Ca2+ transients, but the role of Ca2+ clearance mechanisms and their link to SK channel activity has not been established. Here we report the effect of the Na+/Ca2+ exchanger (NCX) inhibitor benzamil on Ca2+ extrusion and SK channels in the regulation of dendritic Ca2+ signals. Benzamil increased the duration and amplitude of dendritic Ca2+ transients elicited by back-propagating action potentials in hippocampal pyramidal neurons. This data is consistent with previous studies with SK channel blockers and suggests that benzamil inhibits SK channels in addition to the Na+/Ca2+ exchanger. Here we show that indeed both the neuronal SK-mediated IAHP current and the currents mediated by heterologously expressed SK channels were inhibited by benzamil. The inhibition of recombinant SK channels was seen with different K+ concentration gradients, and was stronger at negative voltages. The suppression of SK channels by benzamil is consistent with previous findings on the modulation of Ca2+ signals by SK channels in neurons. We additionally show that benzamil inhibits neuronal voltage-gated calcium currents. The results prompt a careful reassessment of the effects of benzamil on Ca2+ transients in native systems, given the spectrum of ion channels and exchangers this compound targets within a similar range of concentrations.[4]

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In this study, researchers found that amiloride and its analogs inhibit TRPP3 channel activities with different affinities. Radiolabeled (45)Ca2+ uptake showed that TRPP3-mediated Ca2+ transport was inhibited by amiloride, phenamil, Benzamil, and 5-(N-ethyl-N-isopropyl)amiloride (EIPA). Two-microelectrode voltage clamp experiments revealed that TRPP3-mediated Ca2+-activated currents are substantially inhibited by amiloride analogs, in an order of potency of phenamil > Benzamil > EIPA > amiloride, with IC50 values of 0.14, 1.1, 10.5, and 143 microM, respectively. The inhibition potency positively correlated with the size of inhibitors. Using cell-attached patch clamping, we showed that the amiloride analogs decrease the open probability and mean open time but have no effect on single-channel conductance. Study of inhibition by phenamil in the presence of previously reported inhibitor tetrapentylammonium indicates that amiloride and organic cation inhibitors compete for binding the same site on TRPP3. TRPP3 may contribute to previously reported in vivo amiloride-sensitive cation transport[3].

Benzamil, an inhibitor of ENaC that also blocks Na+/Ca2+ exchange (NCX), potentiated myogenic vasoconstriction. Benzamil and low [Na+]o elicited vasoconstriction; however, these responses were attenuated by diltiazem and were associated with significant membrane depolarization, suggesting a contribution of mechanisms other than a reduction in NCX. Na+ repletion induced a vasodilation in pressurized afferent arterioles preequilibrated in low [Na+]o, a hallmark of NCX, and this response was reduced by 10 micromol/l benzamil. The dilation was eliminated, however, by a combination of benzamil plus ouabain, suggesting an involvement of the electrogenic Na+-K+-ATPase. In concert, these findings refute the premise that ENaC plays a significant role in the rat afferent arteriole and instead suggest that reducing [Na+](o) and/or Na+ entry is coupled to membrane depolarization. The mechanisms underlying these unexpected and paradoxical effects of Na+ are not resolved at the present time[2].

Kidneys were allowed to equilibrate for at least 1 h following the establishment of in vitro perfusion. Ibuprofen (10 μmol/l) was added to eliminate the effects of endogenous prostaglandins. Basal renal perfusion pressure was held at 80 mmHg during the equilibration period. In some experiments, myogenic responses were evoked by raising renal arterial pressure and holding pressures at each step for at least 1 min. In these studies, stepped responses were assessed before and after the administration of amiloride or Benzamil. In other experiments, perfusion pressure was maintained at a constant level (60, 80, or 140 mmHg) to assess vasoconstrictor and/or vasodilatory responses. In the studies assessing the impact of low [Na+]o media, the media Na+ concentration ([Na+]) was lowered from 140 to 100 mmol/l by the isosmotic substitution of choline chloride for NaCl. Benzamil, amiloride, and ouabain were obtained commercially. Fresh stock solutions of Benzamil and amiloride were prepared in dimethyl sulfoxide. Ouabain (3 mmol/l in DMEM) was prepared fresh for each experiment. Phentolamine and propranolol (10 μmol/l; Sigma) were added during the ouabain experiments to avoid any effects mediated by neurotransmitter release.[2]

[1]. Characterization of a Na(+)-Ca(2+) exchanger in podocytes. Nephrol Dial Transplant. 2002 Oct;17(10):1742-50.

[2]. Effects of amiloride, benzamil, and alterations in extracellular Na+ on the rat afferent arteriole and its myogenic response. Am J Physiol Renal Physiol. 2008 Jul;295(1):F272-82.

[3]. Inhibition of TRPP3 channel by amiloride and analogs. Mol Pharmacol. 2007 Dec;72(6):1576-85.

[4]. Benzamil inhibits neuronal and heterologously expressed small conductance Ca2+-activated K+channels. Neuropharmacology. 2019 Nov 1;158:107738.

[5]. Epithelial sodium channel inhibition in cardiovascular disease. A potential role for amiloride. Am J Hypertens. 2007 Jan;20(1):109-17.

Benzamil is a member of pyrazines and a member of guanidines.

C13H15CL2N7O

356.2105

319.094

C, 43.83; H, 4.24; Cl, 19.90; N, 27.53; O, 4.49

161804-20-2

Benzamil;2898-76-2

108107

Light yellow to yellow solid powder

2.287

4

6

4

22

413

0

KXDROGADUISDGY-UHFFFAOYSA-N

InChI=1S/C13H14ClN7O/c14-9-11(16)20-10(15)8(19-9)12(22)21-13(17)18-6-7-4-2-1-3-5-7/h1-5H,6H2,(H4,15,16,20)(H3,17,18,21,22)

3,5-diamino-N-(N'-benzylcarbamimidoyl)-6-chloropyrazine-2-carboxamide

Benzamil hydrochloride; 161804-20-2; Benzamil HCl; Benzamil (hydrochloride); Benzylamiloride hydrochloride; Benzamil*HCl; N-(Benzylamidino)-3,5-diamino-6-chloropyrazinecarboxamide hydrochloride; I7L324A070;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 100 mg/mL (~280.73 mM)
H2O : ~1 mg/mL (~2.81 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (7.02 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (7.02 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (7.02 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)