(S)-(-)-Bay-K-8644, the S-enantiomer of Bay-K-8644, is a novel and potent Ca2+ channel activator that activates Ba2+ currents (IBa) with an EC50 of 32 nM. (+/-)-Bay K 8644, a conventional racemic mixture of Bay K 8644, is widely used as an L-type Ca(2+) channel agonist. Although interactions between Bay K 8644 and cyclic nucleotide have been described, they have not been properly characterized. We have investigated whether two optical isomers of Bay K 8644 (i.e., R(+)- and S(-)-Bay K 8644) modify cyclic nucleotide (cAMP and cGMP)-induced inhibitory effects on nifedipine-sensitive voltage-dependent Ba(2+) currents (I (Ba)) recorded from guinea pig gastric myocytes. Conventional whole-cell recordings were used to compare the effects of R(+)-Bay K 8644 and S(-)-Bay K 8644 on I (Ba). S(-)-Bay K 8644 enhanced the peak amplitude of I (Ba) evoked by depolarizing pulses to +10 mV from a holding potential of -70 mV in a concentration-dependent manner (EC(50) = 32 nM), while R(+)-Bay K 8644 inhibited I (Ba) (IC(50) = 975 nM). When R(+)-Bay K 8644 (0.5 microM) was applied, I (Ba) was suppressed to 71 +/- 10% of control. In the presence of R(+)-Bay K 8644 (0.5 microM), additional application of forskolin and sodium nitroprusside (SNP) further inhibited I (Ba). Conversely, in the presence of S(-)-Bay K 8644 (0.5 microM), subsequent application of forskolin and SNP did not affect I (Ba). Similarly, in the presence of 0.5 microM S(-)-Bay K 8644, db-cAMP and 8-Br-cGMP had no effect on I (Ba). These results indicate that S(-)-Bay K 8644, but not R(+)-Bay K 8644, can prevent the inhibitory actions of two distinct cyclic nucleotide pathways on I (Ba) in gastric myocytes of the guinea pig antrum.

Physicochemical Properties

Molecular Formula	C16H15N2O4F3
Molecular Weight	356.2965
Exact Mass	356.098
CAS #	98625-26-4
Related CAS #	Bay K 8644;71145-03-4;(R)-(+)-Bay-K-8644;98791-67-4
PubChem CID	6603728
Appearance	Light yellow to yellow solid powder
Density	1.37g/cm3
Boiling Point	429.2ºC at 760mmHg
Flash Point	213.4ºC
LogP	4.199
Hydrogen Bond Donor Count	1
Hydrogen Bond Acceptor Count	8
Rotatable Bond Count	3
Heavy Atom Count	25
Complexity	634
Defined Atom Stereocenter Count	1
SMILES	CC1=C([C@@H](C(=C(N1)C)[N+](=O)[O-])C2=CC=CC=C2C(F)(F)F)C(=O)OC
InChi Key	ZFLWDHHVRRZMEI-UHFFFAOYSA-N
InChi Code	InChI=1S/C16H15F3N2O4/c1-8-12(15(22)25-3)13(14(21(23)24)9(2)20-8)10-6-4-5-7-11(10)16(17,18)19/h4-7,13,20H,1-3H3
Chemical Name	methyl 2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-1,4-dihydropyridine-3-carboxylate
Synonyms	(S)-(-)-Bay-K-8644; (S)-(-)-Bay K-8644; (-)-BAY R-5417; (-)-BAY-R-5417; (-)-BAY-K-8644; (-)-BAY-K 8644; Bay-K 8644 (S)-(-)-; Bay-K-8644 (S)-(-)-; BAYK 8644; BAYK8644; BAYK-8644.
HS Tariff Code	2934.99.9001
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

Targets	EC50: 32 nM (IBa)[1] (±)-Bay K 8644, a racemic combination of Bay K 8644, is commonly employed as an L-type Ca2+ channel agonist. Each optical isomer has the opposite effect on IBa (R(+)-Bay K 8644 as an antagonist and (S)-(-)-Bay-K-8644 as an agonist. (S)-(-)-Bay-K-8644 can suppress the inhibitory activities of two separate cyclic nucleotide pathways on IBa in guinea pig stomach myocytes[1]. The Ca2+ channel activity is boosted by 3-30 μM (S)-(-)-Bay-K-8644, an agonist of L-type Ca2+ channels (2). The interactions of two Ca2+ channel activators, (S)-(-)-Bay-K-8644 and FPL 64176, are investigated on smooth muscle L-type Ca2+ channels. FPL 64176 (300 nM) produces persistent contractions in rat tail artery strips. The contractile response is approximately 70% reduced by (S)-(-)-Bay-K-8644 (EC50=14 nM). (S)-(-)-Bay-K-8644 (100 nM) boosts whole-cell Ca2+ currents in A7r5 smooth muscle cells but inhibits subsequent stimulation by 1 μM FPL 64176 [3].
ln Vitro	(±)-Bay K 8644, a racemic combination of Bay K 8644, is commonly employed as an L-type Ca2+ channel agonist. Each optical isomer has the opposite effect on IBa (R(+)-Bay K 8644 as an antagonist and (S)-(-)-Bay-K-8644 as an agonist. (S)-(-)-Bay-K-8644 can suppress the inhibitory activities of two separate cyclic nucleotide pathways on IBa in guinea pig stomach myocytes[1]. The Ca2+ channel activity is boosted by 3-30 μM (S)-(-)-Bay-K-8644, an agonist of L-type Ca2+ channels (2). The interactions of two Ca2+ channel activators, (S)-(-)-Bay-K-8644 and FPL 64176, are investigated on smooth muscle L-type Ca2+ channels. FPL 64176 (300 nM) produces persistent contractions in rat tail artery strips. The contractile response is approximately 70% reduced by (S)-(-)-Bay-K-8644 (EC50=14 nM). (S)-(-)-Bay-K-8644 (100 nM) boosts whole-cell Ca2+ currents in A7r5 smooth muscle cells but inhibits subsequent stimulation by 1 μM FPL 64176 [3]. In inspiratory neurons of neonatal mice, application of (S)-(-)-Bay-K-8644 (3–30 µM) enhanced the activity of L-type Ca²⁺ channels recorded in cell-attached patches. The open probability (Popen) of the channels increased approximately 3-fold, and the activation curve was shifted by about 20 mV in the hyperpolarizing direction. In the presence of the agonist, channel open time increased, and long-lasting openings appeared. [2] Agonist-modulated channels (by (S)-(-)-Bay-K-8644 included in the pipette solution) were also potentiated during oxygen depletion (hypoxia). This potentiation was due to an increase in open time and a decrease in closed time. [2] The slope conductance of the L-type Ca²⁺ channels, identified by their sensitivity to (S)-(-)-Bay-K-8644 and dihydropyridine antagonists, was 24 pS below and 50 pS above their null potential when carrying Ba²⁺ currents. [2]
Cell Assay	Experiments were performed on medullary slice preparations from neonatal mice (postnatal days 4–12) containing the functional respiratory network. Slices were continuously superfused with artificial cerebrospinal fluid (ACSF) saturated with carbogen (95% O₂, 5% CO₂) at 28°C. [2] Single L-type Ca²⁺ channel currents were recorded in cell-attached patches from identified inspiratory neurons. Patch pipettes were filled with a solution containing 110 mM BaCl₂ and 10 mM HEPES (pH 7.4). (S)-(-)-Bay-K-8644 (3–30 µM) was either added to the bath or included in the pipette solution. Channel activity was elicited by stepping the holding potential from 0 to +60 mV (corresponding to membrane potentials from -60 to 0 mV, assuming a resting potential of -60 mV). The open probability, open times, and closed times were analyzed from recordings. Channel activity was also assessed during hypoxia induced by replacing O₂ with N₂ in the perfusate. [2] Whole-cell high-voltage-activated Ca²⁺ currents (ICa) were also recorded from inspiratory neurons using an intracellular solution containing caesium and TEA⁺ to block K⁺ channels. The effects of hypoxia on ICa were monitored. [2]
References	[1]. Antagonistic actions of S(-)-Bay K 8644 on cyclic nucleotide-induced inhibition of voltage-dependent Ba(2+) currents in guinea pig gastric antrum. Naunyn Schmiedebergs Arch Pharmacol. 2008 Dec;378(6):609-15. [2]. L-type Ca2+ channels in inspiratory neurones of mice and their modulation by hypoxia. J Physiol. 1998 Oct 1;512 ( Pt 1):75-87. [3]. Functional interactions between two Ca2+ channel activators, (S)-Bay K 8644 and FPL 64176, in smooth muscle. Mol Pharmacol. 1992 Apr;41(4):599-602.
Additional Infomation	(S)-Bay-K-8644 is a methyl 2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-1,4-dihydropyridine-3-carboxylate in which the 4-position has (S)-configuration. It is an enantiomer of a (R)-Bay-K-8644. (S)-(-)-Bay-K-8644 was used as a pharmacological tool to identify and characterize L-type Ca²⁺ channels in neonatal mouse inspiratory neurons. [2] The effects of (S)-(-)-Bay-K-8644 on channel gating (increased Popen, prolonged openings, hyperpolarizing shift in activation) were similar to those observed in other cell types. [2] The activity of L-type Ca²⁺ channels, including those modulated by (S)-(-)-Bay-K-8644, was found to be regulated by intracellular pH and cAMP levels in these neurons. [2] Channels potentiated by (S)-(-)-Bay-K-8644 were further enhanced during hypoxia. [2] The study suggests that L-type Ca²⁺ channels, which can be activated by (S)-(-)-Bay-K-8644, contribute to the early augmentation of the respiratory rhythm during hypoxia, possibly via a pathway involving glutamate release and metabotropic glutamate receptor (mGluR1/5) activation. [2]

Solubility Data

Solubility (In Vitro)

DMSO : ~100 mg/mL (~280.66 mM) H2O : < 0.1 mg/mL

Solubility (In Vivo)

Solubility in Formulation 1: 2.5 mg/mL (7.02 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), suspension solution; with sonication. 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. Solubility in Formulation 2: ≥ 2.08 mg/mL (5.84 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 20.8 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.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	2.8066 mL	14.0331 mL	28.0662 mL
	5 mM	0.5613 mL	2.8066 mL	5.6132 mL
	10 mM	0.2807 mL	1.4033 mL	2.8066 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.