Synthesis of 6-alkoxy and 6-hydroxy-alkyl amine derivatives of braylin as vasorelaxing agents

Braylin (10b) is a 8,8-dimethyl chromenocoumarin present in the plants of the family Rutaceae and Meliaceae and possesses vasorelaxing and anti-inflammatory activities. In this study, six 6-alkoxy (10b, 15-19), and twelve 6-hydroxy-alkyl amine (20a-20l) derivatives of braylin (11 and 12) were synthesized to delineate its structural requirement for vasorelaxing activity. The synthesized compounds were evaluated for vasorelaxation response in preconstricted intact rat Main Mesenteric Artery (MMA). The compounds showed l-type VDCC channel blockade depended and endothelium-independent vasorelaxation within the range of Emax < 50.00-96.70 % at 30 µM. Amongst all, 6-alkoxy derivatives were more active than 6-hydroxy-alkyl amine derivatives. The structural refinements about braylin showed that deletion of its methoxy group or homologation beyond ethoxy group presented deleterious effect on vasorelaxation response of braylin. Interestingly, substituting the ethoxy group in 10b presented the best activity and selectivity towards l-type VDCC channel blockade, a specific target cardiovascular function.

The interactive effects of verapamil and CB1 cannabinoid receptor antagonist/inverse agonist, AM251 on passive avoidance learning and memory in rat

There are reports regarding the effects of intracellular Ca2+ and synthesis and release of endocannabinoids. The secretion of endocannabinoids depends on the L-type calcium channel. The present study evaluated the involvement of the cannabinoid CB1 receptors in the effect of L-type calcium channel blocker verapamil on passive avoidance learning (PAL) in adult male rats. In this study, we examined the effects of an acute administration of the cannabinoid CB1 receptors antagonist/inverse agonist AM251 following a chronic administration of the Ca2+ channel blocker verapamil on PAL. Male Wistar rats were administered verapamil (10, 25 and 50 mg/kg) or saline intraperitoneally (i.p) daily for 13 days (n = 10/group). After this treatment period, a learning test (acquisition) was performed, and a retrieval test was performed the following day. The results indicated that chronic systemic administration of verapamil (in a dose-dependent manner) impaired memory acquisition and retrieval. Pre-training acute administration of a selective CB1 antagonist/inverse agonist, AM251 (5 mg/kg, i.p.) did not change memory acquisition and retrieval. Co-administration of the verapamil and AM251 significantly reversed verapamil-induced amnesia, suggesting a functional interaction between AM251 and verapamil. The results indicated the interactive effects of cannabinoid CB1 receptors and L-type calcium channel in passive avoidance learning and AM251 can counter the effects of verapamil on memory.

Adrenergic Regulation of Calcium Channels in the Heart

Each heartbeat is initiated by the action potential, an electrical signal that depolarizes the plasma membrane and activates a cycle of calcium influx via voltage-gated calcium channels, calcium release via ryanodine receptors, and calcium reuptake and efflux via calcium-ATPase pumps and sodium-calcium exchangers. Agonists of the sympathetic nervous system bind to adrenergic receptors in cardiomyocytes, which, via cascading signal transduction pathways and protein kinase A (PKA), increase the heart rate (chronotropy), the strength of myocardial contraction (inotropy), and the rate of myocardial relaxation (lusitropy). These effects correlate with increased intracellular concentration of calcium, which is required for the augmentation of cardiomyocyte contraction. Despite extensive investigations, the molecular mechanisms underlying sympathetic nervous system regulation of calcium influx in cardiomyocytes have remained elusive over the last 40 years. Recent studies have uncovered the mechanisms underlying this fundamental biologic process, namely that PKA phosphorylates a calcium channel inhibitor, Rad, thereby releasing inhibition and increasing calcium influx. Here, we describe an updated model for how signals from adrenergic agonists are transduced to stimulate calcium influx and contractility in the heart.

Lysophosphatidic Acid Improves Human Sperm Motility by Enhancing Glycolysis and Activating L-Type Calcium Channels

Until now, the molecular mechanisms underlining sperm motility defect causing male infertility are still poorly understood. Safe and effective compounds or drugs that can improve sperm motility are also very limited. Lysophosphatidic acid (LPA) is a naturally occurring phospholipid and a bioactive intermediate with multiple biological activities. It has been detected in various body fluids such as serum, plasma, saliva, tears, blister fluids, hen egg white, and ascites from patients with ovarian cancer. LPA is also abundant in seminal plasma and follicular fluid. It enhances follicle stimulation, improves oocyte fertilization, and promotes early embryonic development and embryo implantation. However, the physiological role of LPA in the male reproductive system remains unknown. Here, our study showed that LPA significantly improved the motility parameters of human sperm hyperactivation in a dose-dependent manner. The LPA-induced elevation of sperm motility is dependent on bovine serum albumin (BSA) but independent of the classical BSA-induced sAC/cAMP/PKA signaling pathway. The enhancement of sperm motility by LPA could not be blocked by CCCP, a respiratory inhibitor suppressing mitochondrial ATP production. Moreover, LPA improved the activity of triosephosphate isomerase in glycolysis. Meanwhile, LPA treatment significantly increased ATP and phosphoenolpyruvate levels and decreased ADP content during sperm glycolysis. Notably, none of known or identified LPA receptors was detected in human sperm. Further investigations showed that LPA promoted sperm motility through L-type calcium channels. In summary, this study revealed the involvement of LPA in the regulation for human sperm motility by enhancing glycolysis and activating L-type calcium channels. The current findings may shed new light on the understanding of causes of asthenozoospermia, and indicate that LPA could be used as a novel therapeutic agent to improve sperm function and fertilizing capacity.

The Physiology, Pathology, and Pharmacology of Voltage-Gated Calcium Channels and Their Future Therapeutic Potential

Voltage-gated calcium channels are required for many key functions in the body. In this review, the different subtypes of voltage-gated calcium channels are described and their physiologic roles and pharmacology are outlined. We describe the current uses of drugs interacting with the different calcium channel subtypes and subunits, as well as specific areas in which there is strong potential for future drug development. Current therapeutic agents include drugs targeting L-type Ca(V)1.2 calcium channels, particularly 1,4-dihydropyridines, which are widely used in the treatment of hypertension. T-type (Ca(V)3) channels are a target of ethosuximide, widely used in absence epilepsy. The auxiliary subunit α2δ-1 is the therapeutic target of the gabapentinoid drugs, which are of value in certain epilepsies and chronic neuropathic pain. The limited use of intrathecal ziconotide, a peptide blocker of N-type (Ca(V)2.2) calcium channels, as a treatment of intractable pain, gives an indication that these channels represent excellent drug targets for various pain conditions. We describe how selectivity for different subtypes of calcium channels (e.g., Ca(V)1.2 and Ca(V)1.3 L-type channels) may be achieved in the future by exploiting differences between channel isoforms in terms of sequence and biophysical properties, variation in splicing in different target tissues, and differences in the properties of the target tissues themselves in terms of membrane potential or firing frequency. Thus, use-dependent blockers of the different isoforms could selectively block calcium channels in particular pathologies, such as nociceptive neurons in pain states or in epileptic brain circuits. Of important future potential are selective Ca(V)1.3 blockers for neuropsychiatric diseases, neuroprotection in Parkinson's disease, and resistant hypertension. In addition, selective or nonselective T-type channel blockers are considered potential therapeutic targets in epilepsy, pain, obesity, sleep, and anxiety. Use-dependent N-type calcium channel blockers are likely to be of therapeutic use in chronic pain conditions. Thus, more selective calcium channel blockers hold promise for therapeutic intervention.

Oxidant stress evoked by pacemaking in dopaminergic neurons is attenuated by DJ-1

Parkinson's disease is a pervasive, ageing-related neurodegenerative disease the cardinal motor symptoms of which reflect the loss of a small group of neurons, the dopaminergic neurons in the substantia nigra pars compacta (SNc). Mitochondrial oxidant stress is widely viewed as being responsible for this loss, but why these particular neurons should be stressed is a mystery. Here we show, using transgenic mice that expressed a redox-sensitive variant of green fluorescent protein targeted to the mitochondrial matrix, that the engagement of plasma membrane L-type calcium channels during normal autonomous pacemaking created an oxidant stress that was specific to vulnerable SNc dopaminergic neurons. The oxidant stress engaged defences that induced transient, mild mitochondrial depolarization or uncoupling. The mild uncoupling was not affected by deletion of cyclophilin D, which is a component of the permeability transition pore, but was attenuated by genipin and purine nucleotides, which are antagonists of cloned uncoupling proteins. Knocking out DJ-1 (also known as PARK7 in humans and Park7 in mice), which is a gene associated with an early-onset form of Parkinson's disease, downregulated the expression of two uncoupling proteins (UCP4 (SLC25A27) and UCP5 (SLC25A14)), compromised calcium-induced uncoupling and increased oxidation of matrix proteins specifically in SNc dopaminergic neurons. Because drugs approved for human use can antagonize calcium entry through L-type channels, these results point to a novel neuroprotective strategy for both idiopathic and familial forms of Parkinson's disease.

Evidence for postsynaptic modulation of muscle contraction by a Drosophila neuropeptide

DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.

Discovery and synthesis of tetrahydroindolone derived semicarbazones as selective Kv1.5 blockers

A novel class of tetrahydroindolone-derived semicarbazones has been discovered as potent Kv1.5 blockers. In in vitro studies, several compounds exhibited very good potency for blockade of Kv1.5. Compound 8i showed good selectivity for blockade of Kv1.5 vs hERG and L-type calcium channels. In an anesthetized pig model, compounds 8i and 10c increased atrial ERP about 28%, 18%, respectively, in the right atrium without affecting ventricular ERP.

Discovery and synthesis of tetrahydroindolone-derived carbamates as Kv1.5 blockers

A novel class of tetrahydroindolone-derived carbamates has been discovered whose members are potent Kv1.5 blockers. The in vitro data show that compounds 6 and 29 are quite potent. They are also very selective over hERG (>450-fold) and L-type calcium channels (>450-fold).

Removal of clustered positive charge from dihydropyridine receptor II-III loop peptide augments activation of ryanodine receptors

Peptides based on the skeletal muscle DHPR II-III loop have been shown to regulate ryanodine receptor channel activity. The N-terminal region of this cytoplasmic loop is predicted to adopt an alpha-helical conformation. We have selected a peptide sequence of 26 residues (Ala(667)-Asp(692)) as the minimum sequence to emulate the helical propensity of the corresponding protein sequence. The interaction of this control peptide with skeletal and cardiac RyR channels in planar lipid bilayers was then assessed and was found to lack isoform specificity. At low concentrations peptide A(667)-D(692) increased RyR open probability, whilst at higher concentrations open probability was reduced. By replacing a region of clustered positive charge with a neutral sequence with the same predisposition to helicity, the inhibitory effect was ablated and activation was enhanced. This novel finding demonstrates that activation does not derive from the presence of positively charged residues adjacent in the primary structure and, although it may be mediated by the alignment of basic residues down one face of an amphipathic helix, not all of these residues are essential.

Functional characterization of the L-type Ca2+ channel Cav1.4alpha1 from mouse retina

PURPOSE

To study the electrophysiological and pharmacological properties of the L-type Ca(2+) channel (LTCC) Ca(v)1.4alpha1 (alpha1F) subunit from mouse retina and assess their contributions to the native retinal channel.

METHODS

The full-length cDNA of Ca(v)1.4alpha1 was cloned from murine retina in an RT-PCR approach. Ca(v)1.4alpha1 was expressed alone or together with the auxiliary alpha2delta1 and beta2a or beta3 subunits in HEK293 cells. The electrophysiological and pharmacological characteristics of L-type Ca(2+) and Ba(2+) inward currents (I(Ca) and I(Ba)) induced by Ca(v)1.4alpha1 were determined by the whole-cell configuration of the patch-clamp method and compared with currents induced by the cardiac and smooth muscle-type Ca(v)1.2alpha1 (alpha1C) channel.

RESULTS

Ca(v)1.4alpha1-mediated I(Ba) was observed only when the alpha2delta1 and beta subunits were coexpressed. Current densities were approximately two times higher with beta2a than with beta3. I(Ba) activated faster and revealed much slower time-dependent inactivation than I(Ba) induced by Ca(v)1.2alpha1. Unlike in Ca(v)1.2alpha1, inactivation was not accelerated with Ca(2+) as the charge carrier, indicating the absence of Ca(2+)-dependent inactivation in Ca(v)1.4alpha1. Ca(v)1.4alpha1 exhibited voltage-dependent inactivation. The dihydropyridine (DHP) antagonist isradipine blocked Ca(v)1.4alpha1 with approximately 20-fold lower sensitivity than Ca(v)1.2alpha1. The agonistic DHP BayK 8644 stimulated maximum I(Ba) approximately sixfold. Ca(v)1.4alpha1 revealed only moderate sensitivities to L- and D-cis-diltiazem, with IC(50) in the micromolar range. Both enantiomers unexpectedly blocked Ca(v)1.4alpha1 with almost equal IC(50).

CONCLUSIONS

The data indicate that Ca(v)1.4alpha1 subunit constitutes the major molecular correlate of retinal L-type Ca(2+) current. Its intrinsic biophysical properties, in particular its unique inactivation properties, enable Ca(v)1.4alpha1 to provide a sustained I(Ca) over a voltage range such as required for tonic glutamate release at the photoreceptor synapse.

Two domains in dihydropyridine receptor activate the skeletal muscle Ca(2+) release channel

The II-III cytoplasmic loop of the skeletal muscle dihydropyridine receptor (DHPR) alpha(1)-subunit is essential for skeletal-type excitation-contraction coupling. Single channel and [(3)H]ryanodine binding studies with a full-length recombinant peptide (p(666-791)) confirmed that this region specifically activates skeletal muscle Ca2+ release channels (CRCs). However, attempts to identify shorter domains of the II-III loop specific for skeletal CRC activation have yielded contradictory results. We assessed the specificity of the interaction of five truncated II-III loop peptides by comparing their effects on skeletal and cardiac CRCs in lipid bilayer experiments; p(671-680) and p(720-765) specifically activated the submaximally Ca2+-activated skeletal CRC in experiments using both mono and divalent ions as current carriers. A third peptide, p(671-690), showed a bimodal activation/inactivation behavior indicating a high-affinity activating and low-affinity inactivating binding site. Two other peptides (p(681-690) and p(681-685)) that contained an RKRRK-motif and have previously been suggested in in vitro studies to be important for skeletal-type E-C coupling, failed to specifically stimulate skeletal CRCs. Noteworthy, p(671-690), p(681-690), and p(681-685) induced similar subconductances and long-lasting channel closings in skeletal and cardiac CRCs, indicating that these peptides interact in an isoform-independent manner with the CRCs.

Effects of dihydropyridine receptor II-III loop peptides on Ca(2+) release in skinned skeletal muscle fibers

In skeletal muscle fibers, the intracellular loop between domains II and III of the alpha(1)-subunit of the dihydropyridine receptor (DHPR) may directly activate the adjacent Ca(2+) release channel in the sarcoplasmic reticulum. We examined the effects of synthetic peptide segments of this loop on Ca(2+) release in mechanically skinned skeletal muscle fibers with functional excitation-contraction coupling. In rat fibers at physiological Mg(2+) concentration ([Mg(2+)]; 1 mM), a 20-residue skeletal muscle DHPR peptide [A(S(20)); Thr(671)-Leu(690); 30 microM], shown previously to induce Ca(2+) release in a triad preparation, caused only small spontaneous force responses in approximately 40% of fibers, although it potentiated responses to depolarization and caffeine in all fibers. The COOH-terminal half of A(S(20)) [A(S(10))] induced much larger spontaneous responses but also caused substantial inhibition of Ca(2+) release to both depolarization and caffeine. Both peptides induced or potentiated Ca(2+) release even when the voltage sensors were inactivated, indicating direct action on the Ca(2+) release channels. The corresponding 20-residue cardiac DHPR peptide [A(C(20)); Thr(793)-Ala(812)] was ineffective, but its COOH-terminal half [A(C(10))] had effects similar to A(S(20)). In the presence of lower [Mg(2+)] (0.2 mM), exposure to either A(S(20)) or A(C(10)) (30 microM) induced substantial Ca(2+) release. Peptide C(S) (100 microM), a loop segment reported to inhibit Ca(2+) release in triads, caused partial inhibition of depolarization-induced Ca(2+) release. In toad fibers, each of the A peptides had effects similar to or greater than those in rat fibers. These findings suggest that the A and C regions of the skeletal DHPR II-III loop may have important roles in vivo.

Reduced verapamil inhibition of endothelin-1-constricted rabbit basilar artery due to enhanced non L-type Ca(2+)-channel-dependent constriction

This study tested whether (1) L-type Ca(2+) channel blockade and extracellular Ca(2+) removal prior to endothelin-1, as compared to during the endothelin-1 constriction, resulted in lesser inhibition, and (2) the reduced inhibition due to prior L-type Ca(2+) channel blockade resulted from enhanced non L-type Ca(2+)-channel-dependent constriction. Pretreatment of rabbit basilar artery in vitro with 1 microM verapamil, an L-type Ca(2+) channel blocker, inhibited 3, 10, 30, and 100 nM endothelin-1 constrictions to a lesser extent than verapamil addition during the plateau endothelin-1 constriction. Ni(2+) (0.03 and 0.1 mM), a nonselective cation channel blocker, relaxed the plateau endothelin-1 constrictions in vessels pretreated with verapamil to greater magnitudes than vessels unexposed to verapamil. Extracellular Ca(2+) removal prior to 10, 30, and 100 nM endothelin-1 also inhibited the endothelin-1 constrictions to smaller magnitudes than Ca(2+) removal during the plateau endothelin-1 constrictions. These results suggest that the reduced inhibition of the endothelin-1 constriction following pretreatment with L-type Ca(2+) channel blocker or Ca(2+)-free solution, as compared to addition of these agents during the endothelin-1 constriction, is the result of non L-type Ca(2+) channel opening and enhanced Ca(2+)-independent constriction, respectively.

Differential activation of brain-derived neurotrophic factor gene promoters I and III by Ca2+ signals evoked via L-type voltage-dependent and N-methyl-D-aspartate receptor Ca2+ channels

Although the brain-derived neurotrophic factor (BDNF) gene is activated by the intracellular Ca(2+) signals evoked via Ca(2+) influx into neurons, little is known about how the activation of alternative BDNF gene promoters is controlled by the Ca(2+) signals evoked via N-methyl-d-aspartate receptors (NMDA-R) and L-type voltage-dependent Ca(2+) channels (L-VDCC). There is a critical range in the membrane depolarization caused by high K(+) concentrations (25-50 mm KCl) for effective BDNF mRNA expression and transcriptional activation of BDNF gene promoters I and III (BDNF-PI and -PIII, respectively) in rat cortical culture. The increase in BDNF mRNA expression induced at high K(+) was repressed not only by nicardipine, an antagonist for L-VDCC, but also by dl-amino-5-phosphonovalerate, an antagonist for NMDA-R, which was supported by the effects of antagonists on the Ca(2+) influx. Although the promoter activations at 25 and 50 mm KCl were different, BDNF-PIII was activated by either the Ca(2+) influx through NMDA-R or L-VDCC, whereas BDNF-PI was predominantly by the Ca(2+) influx through L-VDCC. Direct stimulation of NMDA-R supported the activation of BDNF-PIII but not that of BDNF-PI. Thus, the alternative BDNF gene promoters responded differently to the intracellular Ca(2+) signals evoked via NMDA-R and L-VDCC.