(±)-Bay K 8644

EC50: Acting as a L-type Ca2+ channel activator with EC50 of 17.3 nM .

The advent of calcium channel activators makes it possible to increase the amount of ACh released from the nerve terminals during their activation. Being applied as a Ca2+ channel activator, BAY K 8644 generally exhibits positive inotropic and vasoconstrictor effects on heart and smooth muscle. [1]

In vitro: It was demonstrated that Bay K 8644 prolonged the mean Ca2+ channel opening time in heart myocytes and neurones of spinal ganglia. An experiment using rat heart ventricles demonstrated that Bay K 8644, at the final concentration of approximately 1 pM, had strong positive inotropic effect when added to the perfusion fluid. Moreover, the addition of Bay K 8644 to the chronic ethanol treatment significantly reduced the electrophysiological signs of withdrawal in the isolated hippocampal slices. [2, 3]

In vivo: Study in mice demonstrated that Bay K 8644 significantly ameliorated the ethanol withdrawal syndrome. When experimental animals were administered with an acute injection of Bay K 8644, the convulsive behavior of mice could be monitored to increase for 2 hours. In addition, BAY k 8644 was also reported to ameliorate hypotension in endotoxin-shocked rats. It could lead to a 37% decrease in heart rate of endotoxin-treated rats and 39% decrease in control rats in a dose-dependent manner. [3,4]

Clinical trial: So far, no clinical trial has been conducted.

References:
[1]Greenberg DA, Cooper EC and Carpenter C.  Calcium channel 'agonist' BAY K 8644 inhibits calcium antagonist binding to brain and PC12 cell membranes. Brain Res. 1987. 305: 3658.
[2]Doledal V and Tucek S.  Failure of the calcium channel activator, Bay K 8644, to increase the release of acetylcholine from nerve terminals in brain and diaphragm. Br. J. Pharmac. 1987. 91: 475-9.
[3]Whittington MA, Butterworth AR, Dolin SJ, Patch TL and Little HJ.  The effects of chronic treatment with the dihydropyridine, Bay K 8644, on hyperexcitability due to ethanol withdrawal, in vivo and in vitro. Br. J. Pharmacol. 1992. 105: 285-92.
[4] Ives N, King JW, Chernow B and Roth BL.  BAY k 8644, a calcium channel agonist, reverses hypotension in endotoxin-shocked rats. Eur J Pharmacol. 1986. 130: 169-175.

L-type Ca2+ channel responses to bay k 8644 in stem cell-derived cardiomyocytes are unusually dependent on holding potential and charge carrier.[Pubmed:25147907]

Assay Drug Dev Technol. 2014 Aug;12(6):352-60.

Human stem cell-derived cardiomyocytes provide a cellular model for the study of electrophysiology in the human heart and are finding a niche in the field of safety pharmacology for predicting proarrhythmia. The cardiac L-type Ca2+ channel is an important target for some of these safety studies. However, the pharmacology of this channel in these cells is altered compared to native cardiac tissue, specifically in its sensitivity to the Ca2+ channel activator S-(-)-Bay K 8644. Using patch clamp electrophysiology, we examined the effects of S-(-)-Bay K 8644 in three separate stem cell-derived cardiomyocyte cell lines under various conditions in an effort to detect more typical responses to the drug. S-(-)-Bay K 8644 failed to produce characteristically large increases in current when cells were held at -40 mV and Ca2+ was used as the charge carrier, although high-affinity binding and the effects of the antagonist isomer, R-(+)-Bay K 8644, were intact. Dephosphorylation of the channel with acetylcholine failed to restore the sensitivity of the channel to the drug. Only when the holding potential was shifted to a more hyperpolarized (-60 mV) level, and external Ca2+ was replaced by Ba2+, could large increases in current amplitude be observed. Even under these conditions, increases in current amplitude varied dramatically between different cell lines and channel kinetics following drug addition were generally atypical. The results indicate that the pharmacology of S-(-)-Bay K 8644 in stem cell-derived cardiomyocytes varies by cell type, is unusually dependent on holding potential and charge carrier, and is different from that observed in primary human heart cells.

Failure of Bay K 8644 to induce RhoA kinase-dependent calcium sensitization in rabbit blood vessels.[Pubmed:20590624]

Br J Pharmacol. 2010 Jul;160(6):1326-37.

BACKGROUND AND PURPOSE: RhoA kinase (ROCK) participates in K(+) depolarization (KCl)-induced Ca(2+) sensitization of contraction. Whether constitutive, depolarization- or Ca(2+)-activated ROCK plays the major role in this signalling system remains to be determined. Here, we determined whether Bay K 8644, a dihydropyridine that promotes Ca(2+) channel clusters to operate in a persistent Ca(2+) influx mode, could cause ROCK-dependent Ca(2+) sensitization. EXPERIMENTAL APPROACH: Renal and femoral artery rings from New Zealand white rabbits were contracted with Bay K 8644. Tissues were frozen and processed to measure active RhoA and ROCK substrate (myosin phosphatase targeting subunit, MYPT1) and myosin light chain (MLC) phosphorylation, or loaded with fura-2 to measure intracellular free Ca(2+) ([Ca(2+)](i)). Effects of selective inhibitors of contraction were assessed in resting (basal) tissues and those contracted with Bay K 8644. KEY RESULTS: Bay K 8644 produced strong increases in [Ca(2+)](i), MLC phosphorylation and tension, but not in MYPT1 phosphorylation. ROCK inhibition by H-1152 abolished basal MYPT1-pT853, diminished basal MLC phosphorylation and inhibited Bay K 8644-induced increases in MLC phosphorylation and tension. MLC kinase inhibition by wortmannin abolished Bay K 8644-induced contraction and increase in MLC phosphorylation but did not inhibit basal MYPT1-pT853. H-1152 and wortmannin had no effect on MYPT1-pT696, but 1 microM staurosporine inhibited basal MYPT1-pT853, MYPT1-pT696 and MLC phosphorylation. CONCLUSIONS AND IMPLICATIONS: These data suggest that the constitutive activities of ROCK and a staurosporine-sensitive kinase regulate basal phosphorylation of MYPT1, which participates along with activation of MLC kinase in determining the strength of contraction induced by the Ca(2+) agonist, Bay K 8644.

Quercetin antagonism of Bay K 8644 effects on rat tail artery L-type Ca(2+) channels.[Pubmed:18789318]

Eur J Pharmacol. 2008 Nov 19;598(1-3):75-80.

The functional interaction between two L-type Ca(2+) channel activators, quercetin and (S)-(-)-methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)pyridi ne-5-carboxylate (Bay K 8644), has been investigated in vascular smooth muscle cells. L-type Ca(2+) currents [I(Ca(L))] were recorded in freshly isolated rat tail main artery myocytes using the whole-cell patch-clamp method. Bay K 8644 increased I(Ca(L)) in a concentration-dependent manner with a pEC(50) value of 8.25. Pre-incubation of myocytes with concentrations of quercetin per se ineffective as an L-type Ca(2+) channel activator (0.1 and 0.3 microM) inhibited significantly the maximal response evoked by Bay K 8644, but left unaltered its potency. Quercetin (0.1 microM) prevented the hyperpolarizing shift of the steady-state inactivation curve induced by 0.1 microM Bay K 8644 and its stimulation of I(Ca(L)) tail current intensity without modifying Bay K 8644-induced effects on I(Ca(L)) activation, inactivation, deactivation kinetics as well as on use-dependence and recovery from inactivation. Quercetin at nutritionally meaningful concentrations, limited the responsiveness of vascular L-type Ca(2+) channels to the pharmacological stimulation operated by Bay K 8644. These data contribute to a better understanding of quercetin effects on experimental in vivo cardioprotection.

Antagonistic actions of S(-)-Bay K 8644 on cyclic nucleotide-induced inhibition of voltage-dependent Ba(2+) currents in guinea pig gastric antrum.[Pubmed:18648774]

Naunyn Schmiedebergs Arch Pharmacol. 2008 Dec;378(6):609-15.

(+/-)-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.

Rapamycin and mTOR-independent autophagy inducers ameliorate toxicity of polyglutamine-expanded huntingtin and related proteinopathies.[Pubmed:18636076]

Cell Death Differ. 2009 Jan;16(1):46-56.

The formation of intra-neuronal mutant protein aggregates is a characteristic of several human neurodegenerative disorders, like Alzheimer's disease, Parkinson's disease (PD) and polyglutamine disorders, including Huntington's disease (HD). Autophagy is a major clearance pathway for the removal of mutant huntingtin associated with HD, and many other disease-causing, cytoplasmic, aggregate-prone proteins. Autophagy is negatively regulated by the mammalian target of rapamycin (mTOR) and can be induced in all mammalian cell types by the mTOR inhibitor rapamycin. It can also be induced by a recently described cyclical mTOR-independent pathway, which has multiple drug targets, involving links between Ca(2+)-calpain-G(salpha) and cAMP-Epac-PLC-epsilon-IP(3) signalling. Both pathways enhance the clearance of mutant huntingtin fragments and attenuate polyglutamine toxicity in cell and animal models. The protective effects of rapamycin in vivo are autophagy-dependent. In Drosophila models of various diseases, the benefits of rapamycin are lost when the expression of different autophagy genes is reduced, implicating that its effects are not mediated by autophagy-independent processes (like mild translation suppression). Also, the mTOR-independent autophagy enhancers have no effects on mutant protein clearance in autophagy-deficient cells. In this review, we describe various drugs and pathways inducing autophagy, which may be potential therapeutic approaches for HD and related conditions.

Induction of pluripotent stem cells from mouse embryonic fibroblasts by Oct4 and Klf4 with small-molecule compounds.[Pubmed:18983970]

Cell Stem Cell. 2008 Nov 6;3(5):568-74.

Somatic cells can be induced into pluripotent stem cells (iPSCs) with a combination of four transcription factors, Oct4/Sox2/Klf4/c-Myc or Oct4/Sox2/Nanog/LIN28. This provides an enabling platform to obtain patient-specific cells for various therapeutic and research applications. However, several problems remain for this approach to be therapeutically relevant due to drawbacks associated with efficiency and viral genome integration. Recently, it was shown that neural progenitor cells (NPCs) transduced with Oct4/Klf4 can be reprogrammed into iPSCs. However, NPCs express Sox2 endogenously, possibly facilitating reprogramming in the absence of exogenous Sox2. In this study, we identified a small-molecule combination, BIX-01294 and BayK8644, that enables reprogramming of Oct4/Klf4-transduced mouse embryonic fibroblasts, which do not endogenously express the factors essential for reprogramming. This study demonstrates that small molecules identified through a phenotypic screen can compensate for viral transduction of critical factors, such as Sox2, and improve reprogramming efficiency.

Central and peripheral effects of the dihydropyridine calcium channel activator BAY K 8644 in the rat.[Pubmed:2469593]

Eur J Pharmacol. 1989 Feb 7;160(3):339-47.

Following intraperitoneal (i.p.) administration BAY K 8644 (0.5-4 mg/kg) induced an increase in blood pressure associated with bradycardia, increased tail-flick latency in response to radiant heat, decreased locomotion, induced muscle contraction, postural changes and also reduced reflex activity. Only the postural changes and reduced locomotion were seen after intracerebroventricular administration (5-20 micrograms/kg), suggesting that the other effects are mediated peripherally. All the above effects were antagonised by the calcium channel blocker nifedipine. BAY K 8644 (4 mg/kg i.p.) also significantly increased homovanillic acid and 3,4-dihydroxyphenylacetic acid concentrations in the cortex and striatum, an effect which could also be reversed by nifedipine. Apart from inducing hypotension and tachycardia, nifedipine alone had no effect on any of the above parameters. The analgesic-like activity of BAY K 8644 observed in the tail-flick test appears to be related to its vasoconstrictor effects as the peripherally acting vasodilator phenylephrine had similar analgesic activity. These results show that both central and peripheral dihydropyridine-sensitive calcium channels mediate the effects of BAY K 8644. Although a physiological role for the dihydropyridine-sensitive voltage-operated calcium channel in the CNS remains to be demonstrated, activation of these channels can clearly have functional effects.

Calcium channel 'agonist' BAY K 8644 inhibits calcium antagonist binding to brain and PC12 cell membranes.[Pubmed:6204725]

Brain Res. 1984 Jul 9;305(2):365-8.

BAY K 8644, a drug that elicits calcium-dependent muscle contraction, inhibits binding of the voltage-dependent calcium channel antagonist [3H]nitrendipine to brain and PC12 pheochromocytoma cell membranes. This effect is due to high-affinity (Ki = 4.5 nM) competitive inhibition at the binding site for dihydropyridine calcium antagonists. Allosteric sites that mediate calcium channel blockade by non-dihydropyridine calcium antagonists are not similarly affected. Our findings indicate that BAY K 8644 is active at central, as well as peripheral, calcium channels and are compatible with a multi-state model of the voltage-dependent calcium channel in which antagonist drugs promote a closed state of the channel, while BAY K 8644 promotes an open state.