Blockade Of L-type Calcium Channels Research Articles

Hippocampal hyperphosphorylated tau-induced deficiency is rescued by L-type calcium channel blockade.

Aging and Alzheimer's disease are associated with chronic elevations in neuronal calcium influx via L-type calcium channels. The hippocampus, a primary memory encoding structure in the brain, is more vulnerable to calcium dysregulation in Alzheimer's disease. Recent research has suggested a link between L-type calcium channels and tau hyperphosphorylation. However, the precise mechanism of L-type calcium channel-mediated tau toxicity is not understood. In this study, we seeded a human tau pseudophosphorylated at 14 amino acid sites in rat hippocampal cornu ammonis 1 region to mimic soluble pretangle tau. Impaired spatial learning was observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats as early as 1-3 months and worsened at 9-10 months post-infusion. Rats infused with wild-type human tau exhibited milder behavioural deficiency only at 9-10 months post-infusion. No tangles or plaques were observed in all time points examined in both human tau pseudophosphorylated at 14 amino acid sites and human tau-infused brains. However, human tau pseudophosphorylated at 14 amino acid sites-infused hippocampus exhibited a higher amount of tau phosphorylation at S262 and S356 than the human tau-infused rats at 3 months post-infusion, paralleling the behavioural deficiency observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats. Neuroinflammation indexed by increased Iba1 in the cornu ammonis 1 was observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats at 1-3 but not 9 months post-infusion. Spatial learning deficiency in human tau pseudophosphorylated at 14 amino acid sites-infused rats at 1-3 months post-infusion was paralleled by decreased neuronal excitability, impaired NMDA receptor-dependent long-term potentiation and augmented L-type calcium channel-dependent long-term potentiation at the cornu ammonis 1 synapses. L-type calcium channel expression was elevated in the soma of the cornu ammonis 1 neurons in human tau pseudophosphorylated at 14 amino acid sites-infused rats. Chronic L-type calcium channel blockade with nimodipine injections for 6 weeks normalized neuronal excitability and synaptic plasticity and rescued spatial learning deficiency in human tau pseudophosphorylated at 14 amino acid sites-infused rats. The early onset of L-type calcium channel-mediated pretangle tau pathology and rectification by nimodipine in our model have significant implications for preclinical Alzheimer's disease prevention and intervention.

The Promise of Cilnidipine in Hypertension with Comorbidities: National Consensus Statement: National Consensus Group Comprises Cardiologists, Nephrologists, and Diabetologists from India in a National Meet at New Delhi held on 22nd May 2022.

The rapidly increasing burden of hypertension is responsible for premature deaths from cardiovascular disease (CVD), renal disease, and stroke, with a tremendous public health and financial burden. Hypertension detection, treatment, and control vary worldwide; it is still low, particularly in low- and middle-income countries (LMICs). High blood pressure (BP) and CVD risk have a strong, linear, and independent association. They contribute to alarming numbers of all-cause and CVD deaths. A major culprit for increased hypertension is sympathetic activity, and further complications of hypertension are heart failure, ischemic heart disease (IHD), stroke, and renal failure. Now, antihypertensive interventions have emerged as a global public health priority to reduce BP-related morbidity and mortality. Calcium channel blockers (CCB) are highly effective vasodilators. and the most common drugs used for managing hypertension and CVD. Cilnidipine, with both L- and N-type calcium channel blocking activity, is a promising 4th generation CCB. It causes vasodilation via L-type calcium channel blockade and inhibits the sympathetic nervous system (SNS) via N-type calcium channel blockade. Cilnidipine, which acts as a dual L/N-type CCB, is linked to a reduced occurrence of pedal edema compared to amlodipine, which solely blocks L-type calcium channels. The antihypertensive properties of cilnidipine are very substantial, with low BP variability and long-acting properties. It is beneficial for hypertensive patients to deal with morning hypertension and for patients with abnormal nocturnal BP due to exaggerated sympathetic nerve activation. Besides its BP-lowering effect, it also exhibits organ protection via sympathetic nerve inhibition and renin-angiotensin-aldosterone system inhibition; it controls heart rate and proteinuria. Reno-protective, neuroprotective, and cardioprotective effects of cilnidipine have been well-documented and demonstrated.

A subfraction obtained from the venom of the tarantula Poecilotheria regalis contains inhibitor cystine knot peptides and induces relaxation of rat aorta by inhibiting L-type voltage-gated calcium channels.

Venoms from tarantulas contain low molecular weight vasodilatory compounds whose biological action is conceived as part of the envenomation strategy due to its propagative effects. However, some properties of venom-induced vasodilation do not match those described by such compounds, suggesting that other toxins may cooperate with these ones to produce the observed biological effect. Owing to the distribution and function of voltage-gated ion channels in blood vessels, disulfide-rich peptides isolated from venoms of tarantulas could be conceived into potential vasodilatory compounds. However, only two peptides isolated from spider venoms have been investigated so far. This study describes for the first time a subfraction containing inhibitor cystine knot peptides, PrFr-I, obtained from the venom of the tarantula Poecilotheria regalis. This subfraction induced sustained vasodilation in rat aortic rings independent of vascular endothelium and endothelial ion channels. Furthermore, PrFr-I decreased calcium-induced contraction of rat aortic segments and reduced extracellular calcium influx to chromaffin cells by the blockade of L-type voltage-gated calcium channels. This mechanism was unrelated to the activation of potassium channels from vascular smooth muscle, since vasodilation was not affected in the presence of TEA, and PrFr-I did not modify the conductance of the voltage-gated potassium channel Kv10.1. This work proposes a new envenomating function of peptides from venoms of tarantulas, and establishes a new mechanism for venom-induced vasodilation.

Essential oil of Sicilian Prangos ferulacea (L.) Lindl. and its major component, β−ocimen, affect contractility in rat small and large intestine

Ethnopharmacological relevancePrangos ferulacea (L.) Lindl is an Apiaceae plant, widely used in traditional medicine. Recently, chemical composition and biological activities of its essential oil (Prangroil) have been reported, but there are no studies on possible effects on intestinal contractility. Aims of the studyWe investigated the effects of essential oil Sicilian Prangoil on the contractility of rat small (duodenum) and large (colon) intestine and the related action mechanism. Materials and methodsResponses to Prangoil and to its major component β−ocimen in intestinal segments were assessed in vitro as changes in isometric tension. ResultsPrangoil, induced in duodenum, depending upon doses, contraction and/or muscular relaxation. Instead, in colon Prangoil only reduced the phasic contractions and induced muscular relaxation. β−ocimen, in both segments, produced only reduction of the spontaneous contractions without affecting basal tone. Prangoil contractile effects were abolished by ω-conotoxin, neural N-type Ca2+ channels blocker, atropine, muscarinic receptor antagonist, neostigmine, acetylcholinesterase (AChE) inhibitor, suggesting that Prangoil-induced contraction would be the result of an increase in neuronal cholinergic activity. Prangoil and β−ocimen inhibitory effects were unaffected by ω−conotoxin, L-NAME, blocker of the NO synthase, ODQ, soluble guanylate cyclase inhibitor, excluding involvement of neurotransmitter release or NO synthesis in the inhibitory effects. Potassium channel blocker did not affect Prangoil or β-ocimen inhibitory responses. Prangoil or β-ocimen inhibited the Ca2+ and high-KCl solution -induced contractions and the Carbachol-induced contractions in calcium free solution. ConclusionPrangoil affects the contractility of small and large intestine in rat, with regional differences, via potentiation of neural cholinergic activity, blockade of L-type voltage-gated calcium channel and reduction of Ca2+ release from the intracellular store. The Prangroil main components, β−ocimen, contributes to the inhibitory effects.

Antiarrhythmic calcium channel blocker verapamil inhibits trek currents in sympathetic neurons.

Background and Purpose: Verapamil, a drug widely used in certain cardiac pathologies, exert its therapeutic effect mainly through the blockade of cardiac L-type calcium channels. However, we also know that both voltage-dependent and certain potassium channels are blocked by verapamil. Because sympathetic neurons of the superior cervical ganglion (SCG) are known to express a good variety of potassium currents, and to finely tune cardiac activity, we speculated that the effect of verapamil on these SCG potassium channels could explain part of the therapeutic action of this drug. To address this question, we decided to study, the effects of verapamil on three different potassium currents observed in SCG neurons: delayed rectifier, A-type and TREK (a subfamily of K2P channels) currents. We also investigated the effect of verapamil on the electrical behavior of sympathetic SCG neurons. Experimental Approach: We employed the Patch-Clamp technique to mouse SCG neurons in culture. Key Results: We found that verapamil depolarizes of the resting membrane potential of SCG neurons. Moreover, we demonstrated that this drug also inhibits A-type potassium currents. Finally, and most importantly, we revealed that the current driven through TREK channels is also inhibited in the presence of verapamil. Conclusion and Implications: We have shown that verapamil causes a clear alteration of excitability in sympathetic nerve cells. This fact undoubtedly leads to an alteration of the sympathetic-parasympathetic balance which may affect cardiac function. Therefore, we propose that these possible peripheral alterations in the autonomic system should be taken into consideration in the prescription of this drug.

6-Amino-3-Methyl-4-(2-nitrophenyl)-1,4-Dihydropyrano[2,3-c]Pyrazole-5-Carbonitrile Shows Antihypertensive and Vasorelaxant Action via Calcium Channel Blockade.

Several 4H-pyran derivatives were designed and synthesized previously as vasorelaxant agents for potential antihypertensive drugs. In this context, the objective of the present investigation was to determine the functional mechanism of vasorelaxant action of 6-amino-3-methyl-4-(2-nitrophenyl)-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (1: ) and its in vivo antihypertensive effect. Thus, compound 1: showed significant vasorelaxant action on isolated aorta rat rings pre-contracted with serotonin or noradrenaline, and the effect was not endothelium-dependent. Compound 1: induced a significant relaxant effect when aortic rings were contracted with KCl (80 mM), indicating that the main mechanism of action is related to L-type calcium channel blockade. Last was corroborated since compound 1: induced a significant concentration-dependent lowering of contraction provoked by cumulative CaCl2 adding. Moreover, compound 1: was capable to block the contraction induced by FPL 64176, a specific L-type calcium channel agonist, in a concentration-dependent manner. On the other hand, docking studies revealed that compound 1: interacts on two possible sites of the L-type calcium channel and it had better affinity energy (-7.80+/-0.00 kcal/mol on the best poses) than nifedipine (-6.86+/-0.14 kcal/mol). Finally, compound 1: (50 mg/kg) showed significant antihypertensive activity, lowering the systolic and diastolic blood pressure on spontaneously hypertensive rats (SHR) without modifying heart rate.

Identification of a novel distension-evoked motility pattern in the mouse uterus.

The dynamic changes in uterine contractility in response to distension are incompletely understood. Rhythmic, propagating contractions of nonpregnant uterine smooth muscle occur in the absence of nerve activity (i.e., myogenic), events that decline during pregnancy and reemerge at parturition. We therefore sought to determine how myogenic contractions of the nonpregnant uterus are affected by distension, which might provide mechanistic clues underlying distension-associated uterine conditions such as preterm birth. Uteri isolated from nulliparous adult female mice in proestrus were video imaged to generate spatiotemporal maps, and myoelectrical activity simultaneously recorded using extracellular suction electrodes. Motility patterns were examined under basal conditions and following ramped intraluminal distension with fluid to 5 and 10 cmH2O. Intraluminal distension caused pressure-dependent changes in the frequency, amplitude, propagation speed, and directionality of uterine contractions, which reversed upon pressure release. Altered burst durations of underlying smooth muscle myoelectric events were concurrently observed, although action potential spike intervals were unchanged. Voltage-gated sodium channel blockade [tetrodotoxin (TTX); 0.6 µM] attenuated both the amplitude of contractions and burst duration of action potentials, whereas all activity was abolished by L-type calcium channel blockade (nifedipine; 1 µM). These data suggest that myogenic motility patterns of the nonpregnant mouse uterus are sensitive to changes in intraluminal pressure and, at high pressures, may be modulated by voltage-gated sodium channel activity. Future studies may investigate whether similar distension-evoked changes occur in the pregnant uterus and the possible pathophysiological role of such activity in the development of preterm birth.

Specific Localization of an Auto-inhibition Mechanism at Presynaptic Terminals of Identified Serotonergic Neurons

Auto-regulation mechanisms in serotonergic neurons regulate their electrical activity and secretion. Since these neurons release serotonin from different structural compartments – including presynaptic terminals, soma, axons and dendrites – through different mechanisms, autoregulation mechanisms are also likely to be different at each compartment. Here we show that a chloride-mediated auto-inhibitory mechanism is exclusively localized at presynaptic terminals, but not at extrasynaptic release sites, in serotonergic Retzius neurons of the leech. An auto-inhibition response was observed immediately after intracellular stimulation with an electrode placed in the soma, in neurons that were isolated and cultured retaining an axonal stump, where presynaptic terminals are formed near the soma, but not in somata isolated without axon, where no synaptic terminals are formed, nor in neurons in the nerve ganglion, where terminals are electrotonically distant from the soma. Furthermore, no auto-inhibition response was detected in either condition during the longer time course of somatic secretion. This shows that the auto-inhibition effects are unique to nerve terminals. We further determined that serotonin released from peri-synaptic dense-core vesicles contributes to auto-inhibition in the terminals, since blockade of L-type calcium channels, which are required to stimulate extrasynaptic but not synaptic release, decreased the amplitude of the auto-inhibition response. Our results show that the auto-regulation mechanism at presynaptic terminals is unique and different from that described in the soma of these neurons, further highlighting the differences in the mechanisms regulating serotonin release from different neuronal compartments, which expand the possibilities of a single neuron to perform multiple functions in the nervous system.

Chemical and Pharmacological Screening of Rhinella icterica (Spix 1824) Toad Parotoid Secretion in Avian Preparations.

The biological activity of Rhinella icterica parotoid secretion (RIPS) and some of its chromatographic fractions (RI18, RI19, RI23, and RI24) was evaluated in the current study. Mass spectrometry of these fractions indicated the presence of sarmentogenin, argentinogenin, (5β,12β)-12,14-dihydroxy-11-oxobufa-3,20,22-trienolide, marinobufagin, bufogenin B, 11α,19-dihydroxy-telocinobufagin, bufotalin, monohydroxylbufotalin, 19-oxo-cinobufagin, 3α,12β,25,26-tetrahydroxy-7-oxo-5β-cholestane-26-O-sulfate, and cinobufagin-3-hemisuberate that were identified as alkaloid and steroid compounds, in addition to marinoic acid and N-methyl-5-hydroxy-tryptamine. In chick brain slices, all fractions caused a slight decrease in cell viability, as also seen with the highest concentration of RIPS tested. In chick biventer cervicis neuromuscular preparations, RIPS and all four fractions significantly inhibited junctional acetylcholinesterase (AChE) activity. In this preparation, only fraction RI23 completely mimicked the pharmacological profile of RIPS, which included a transient facilitation in the amplitude of muscle twitches followed by progressive and complete neuromuscular blockade. Mass spectrometric analysis showed that RI23 consisted predominantly of bufogenins, a class of steroidal compounds known for their cardiotonic activity mediated by a digoxin- or ouabain-like action and the blockade of voltage-dependent L-type calcium channels. These findings indicate that the pharmacological activities of RI23 (and RIPS) are probably mediated by: (1) inhibition of AChE activity that increases the junctional content of Ach; (2) inhibition of neuronal Na+/K+-ATPase, leading to facilitation followed by neuromuscular blockade; and (3) blockade of voltage-dependent Ca2+ channels, leading to stabilization of the motor endplate membrane.

Severe Calcium Channel Blocker Overdose and Successful Management: a Case Report and Literature Review

Background: Calcium channel blocker (CCB) toxicity is one of the most lethal and common drug overdoses encountered in the emergency department (ED). The toxicity of these drugs results from blockade of L-type calcium channels in smooth cells, myocardial cells, and beta cells of the pancreas. Severe toxicity can result in bradycardia, hypotension, hyperglycemia, metabolic acidosis, shock, cardiac arrest and death. According to the American Association of Poison Control Centers’ National Poison Data System’s annual report in 2015, cardiovascular medications were the fourth most common adult poisoning exposure and second most common cause of adult poisoning fatality in the USA. CCBs are responsible for a substantial portion of the mortality associated with cardiovascular medication overdose cases. Understanding the emergent management of CCB toxicity is essential. Treatment of patients with CCB overdose remains challenging especially in those with refractory hypotension and end organ dysfunction. Case Presentation: A 45-year-old male with massive amlodipine overdose presented to ED with syncope and severe hypotension. Intensive medical therapy (fluid resuscitation, inotropes, calcium gluconate, and hyperinsulinemia euglycemia therapy [HIET]) was initiated in the ED and continued in the Intensive Care Unit (ICU), and resulted in the patient’s total recovery, without any major complications. Fortunately, ECMO implantation (extracorporeal membrane oxygenation) was not required in this patient. Conclusion: Urgent administration of fluids, calcium, vasopressors, and HIET therapy seem to be the most well validated initial approaches to CCBs overdose treatment. Our successful management strategy should serve as a good learning experience as well as a recommendation for managing such patients.

Development of an adverse outcome pathway (AOP) for cardiotoxicity mediated by the blockade of L-type calcium channels

Development of an adverse outcome pathway (AOP) for cardiotoxicity mediated by the blockade of L-type calcium channels

Myogenic tone contributes to the regulation of permeability in mesenteric microvessels

The microvascular endothelium plays a key role in regulating solute permeability in the gut, but the contribution of vascular smooth muscle to barrier function is unknown. We sought to determine the role of vascular smooth muscle and its myogenic tone in the vascular barrier to solutes in mesenteric microvessels. We determined vascular permeability to 4.4 kDa and 70 kDa dextrans in isolated mouse mesenteric arteries at increasing pressure increments. The myogenic response was simultaneously monitored using video edge-detection of vessel diameter and wall thickness. We expressed permeability as the apparent permeability coefficient, or the solute flux per second normalized to surface area and concentration gradient. We compared the effects of myogenic tone, L-type calcium channel blockade, calcium elimination, and endothelial removal on the permeability of each dextran. We found arteries resisted changes in 4.4 kDa and 70 kDa dextran permeability coefficients at intravascular pressures associated with myogenic tone. Manipulations that reduced or eliminated myogenic tone (L-type calcium channel blockade or calcium elimination) caused vasodilation and increased permeability coefficients. Thus, the maintenance of a reactive mesenteric vascular smooth muscle layer and its myogenic tone prevents increases in vascular permeability that would otherwise occur with increasing pressure. Conditions that impact vascular tone, such as trauma, stroke, or major surgery could diminish the gut-vascular barrier against dissemination of the microbiome.

Lipid emulsion inhibits the vasodilation induced by a toxic dose of amlodipine in isolated rat aortae.

The goal of this study was to examine the effect of lipid emulsion on the vasodilation induced in isolated endothelium-denuded rat aortae by a toxic dose of amlodipine. We examined the effects of lipid emulsion and verapamil on amlodipine-induced vasodilation. We also examined the effects of a mixture of lipid emulsion and amlodipine, as well as the centrifuged aqueous extract (CAE) obtained by ultracentrifuging such a mixture and then removing the upper lipid layer, on amlodipine-induced vasodilation. The effect of lipid emulsion on the amlodipine concentration was examined. Lipid emulsion attenuated amlodipine-induced vasodilation in isolated aortae. Both CAE and lipid emulsion containing amlodipine inhibited amlodipine-induced vasodilation. However, there was no significant difference in amlodipine-induced vasodilation between aortae treated with CAE and those treated with lipid emulsion containing amlodipine. Verapamil inhibited amlodipine-induced vasodilation. Lipid emulsion decreased the concentration of amlodipine. Lipid emulsion attenuated the vasodilation induced by a toxic amlodipine dose in NaF-precontracted aortae. The data show that lipid emulsion inhibited the vasodilation induced by a toxic amlodipine dose in isolated rat aortae by reducing the concentration of amlodipine. Amlodipine-induced vasodilation seems to be mediated mainly by blockade of L-type calcium channels and partially by inhibition of the Rho-kinase pathway.

Mechanism of P2X7 receptor-dependent enhancement of neuromuscular transmission in pannexin 1 knockout mice.

P2X7 receptors are present in presynaptic membranes of motor synapses, but their regulatory role in modulation of neurotransmitter release remains poorly understood. P2X7 receptors may interact with pannexin 1 channels to form a purinergic signaling unit. The potential mechanism of P2X7 receptor-dependent modulation of acetylcholine (ACh) release was investigated by recording miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) in neuromuscular junctions of wild-type (WT) and pannexin 1 knockout (Panx1-/-) mice. Modulation of P2X7 receptors with the selective inhibitor A740003 or the selective agonist BzATP did not alter the parameters of either spontaneous or evoked ACh release in WT mice. In Panx1-/- mice, BzATP-induced activation of P2X7 receptors resulted in a uniformly increased quantal content of EPPs during a short stimulation train. This effect was accompanied by an increase in the size of the readily releasable pool, while the release probability did not change. Inhibition of calmodulin by W-7 or of calcium/calmodulin-dependent kinase II (CaMKII) by KN-93 completely prevented the potentiating effect of BzATP on the EPP quantal content. The blockade of L-type calcium channels also prevented BzATP action on evoked synaptic activity. Thus, the activation of presynaptic P2X7 receptors in mice lacking pannexin 1 resulted in enhanced evoked ACh release. Such enhanced release was provoked by triggering the calmodulin- and CaMKII-dependent signaling pathway, followed by activation of presynaptic L-type calcium channels. We suggest that in WT mice, this pathway is downregulated due to pannexin 1-dependent tonic activation of inhibitory presynaptic purinergic receptors, which overcomes P2X7-mediated effects.

Nimodipine confers clinical improvement in two models of experimental autoimmune encephalomyelitis.

Multiple sclerosis is characterised by inflammatory neurodegeneration, with axonal injury and neuronal cell death occurring in parallel to demyelination. Regarding the molecular mechanisms responsible for demyelination and axonopathy, energy failure, aberrant expression of ion channels and excitotoxicity have been suggested to lead to Ca2+ overload and subsequent activation of calcium-dependent damage pathways. Thus, the inhibition of Ca2+ influx by pharmacological modulation of Ca2+ channels may represent a novel neuroprotective strategy in the treatment of secondary axonopathy. We therefore investigated the effects of the L-type voltage-gated calcium channel blocker nimodipine in two different models of mouse experimental autoimmune encephalomyelitis (EAE), an established experimental paradigm for multiple sclerosis. We show that preventive application of nimodipine (10mg/kg per day) starting on the day of induction had ameliorating effects on EAE in SJL/J mice immunised with encephalitic myelin peptide PLP139-151 , specifically in late-stage disease. Furthermore, supporting these data, administration of nimodipine to MOG35-55 -immunised C57BL/6 mice starting at the peak of pre-established disease, also led to a significant decrease in disease score, indicating a protective effect on secondary CNS damage. Histological analysis confirmed that nimodipine attenuated demyelination, axonal loss andpathological axonal β-amyloid precursor protein accumulation in the cerebellum and spinal cord in the chronic phase of disease. Of note, we observed no effects of nimodipine on the peripheral immune response in EAE mice with regard to distribution, antigen-specific proliferation or activation patterns of lymphocytes. Taken together, our data suggest a CNS-specific effect of L-type voltage-gated calcium channel blockade to inflammation-induced neurodegeneration.

Diethyl-4,4ʹ-dihydroxy-8,3ʹ-neolign-7,7ʹ-dien-9,9ʹ-dionate exhibits antihypertensive activity in rats through increase in intracellular cGMP level and blockade of calcium channels

We report here the antihypertensive and vasorelaxant potential of some steroidal and non-steroidal compounds identified through a library of compounds. All the novel analogues showed vasorelaxant potential in isolated rat aorta. The most potent lead neolignan1 (Diethyl-4,4ʹ-dihydroxy-8,3ʹ-neolign-7,7ʹ-dien-9,9ʹ-dionate) produced concentration dependent relaxation with [pD2 5.16±0.05; n=16 and Emax 96.97%±1.12%; n=16]. The neolignan1 relaxation is independent of endothelium and is sensitive to ODQ (1H-[1, 2, 4] oxadiazolo [4, 3-a] quinoxalin-1-one; a blocker of soluble guanylyl cyclase (sGC) which synthesizes cGMP (cyclic guanosine monophosphate)). ELISA analysis of treated arterial tissues showed concentration-dependent increase in cGMP level in treated tissues compared to control (2.03 and 7.16 fold of control at 10 and 30µM of neolignan1, respectively) and a synergistic increase in cGMP level by 26.66 fold compared to control when used in combination with sildenafil (10µM; a known inducer of cGMP level by selectively blocking cGMP specific phosphodiesterase 5). Our present study reports for the first time that neolignans produce relaxation in isolated rat aorta through increase in intracellular cGMP level. The ODQ resistant relaxation of neolignan1 is mediated by blockade of voltage dependent L-type calcium channel (VDCC) as observed in the experiment with CaCl2. Neolignan1 upon intravenous administration via tail vein in Spontaneously Hypertensive Rats (SHR) produced significant decrease in systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial blood pressure (MAP). The present study concludes that neolignan1 exhibited antihypertensive potential in rats through rise in intracellular cGMP and blockade of VDCC.

Progesterone analogue protects stressed photoreceptors via bFGF-mediated calcium influx.

Retinitis pigmentosa (RP) is a degenerative retinal disease leading to photoreceptor cell loss. In 2011, our group identified the synthetic progesterone 'Norgestrel' as a potential treatment for RP. Subsequent research showed Norgestrel to work through progesterone receptor membrane component 1 (PGRMC1) activation and upregulation of neuroprotective basic fibroblast growth factor (bFGF). Using trophic factor deprivation of 661W photoreceptor-like cells, we aimed to further elucidate the mechanism leading to Norgestrel-induced neuroprotection. In the present manuscript, we show by flow cytometry and live-cell immunofluorescence that Norgestrel induces an increase in cytosolic calcium in both healthy and stressed 661Ws over 24h. Specific PGRMC1 inhibition by AG205 (1μm) showed this rise to be PGRMC1-dependent, primarily utilizing calcium from extracellular sources, for blockade of L-type calcium channels by verapamil (50μm) prevented a Norgestrel-induced calcium influx in stressed cells. Calcium influx was also shown to be bFGF-dependent, for siRNA knock down of bFGF prevented Norgestrel-PGRMC1 induced changes in cytosolic calcium. Notably, we demonstrate PGRMC1-activation is necessary for Norgestrel-induced bFGF upregulation. We propose that Norgestrel protects through the following pathway: binding to and activating PGRMC1 expressed on the surface of photoreceptor cells, PGRMC1 activation drives bFGF upregulation and subsequent calcium influx. Importantly, raised intracellular calcium is critical to Norgestrel's protective efficacy, for extracellular calcium chelation by EGTA abrogates the protective effects of Norgestrel on stressed 661W cells invitro.

In vitro vasodilatory activity and possible mechanisms of the crude extracts and fractions of Moringa stenopetala (Baker f.) Cufod. leaves in isolated thoracic aorta of guinea pigs.

Moringa stenopetala, a plant belonging to the family of Moringaceae, is traditionally used for the treatment of hypertension and diabetes in Ethiopia. This study evaluates the in vitro vasodilatory effect of the extract of M. stenopetala leaves and the possible mechanisms in precontracted isolated thoracic aorta of guinea pigs. A guinea pig was sacrificed by gentle cervical dislocation, and the thoracic aortic ring was removed, cut spirally, and mounted in an organ bath containing Krebs–Henseleit physiological solution maintained at 37°C, and then the solution was aerated with carbogen (95% O2 and 5% CO2). The vasodilatory activity of cumulative doses of M. stenopetala extracts and fractions was evaluated on intact and denuded endothelium of isolated whole, spirally cut thoracic aortic strips of guinea pigs precontracted with potassium chloride (80 mM), epinephrine (1 μM), methylene blue (10 μM), and glibenclamide (10 μM) using polygraph. All extracts showed a relaxant effect in precontracted isolated whole, spirally cut thoracic aortic strips of guinea pigs in a dose-dependent manner, whereas the greater percentage of relaxant effect was shown with the addition of crude extracts in 80 mM of potassium chloride (99.10% and 95.56% for ethanol and aqueous crude extracts, respectively), and 1 μM of epinephrine (82.85% and 90.16% for ethanol and aqueous crude extracts, respectively) in precontracted isolated whole, spirally cut thoracic aortic strips of guinea pigs. Hence, the possible mechanism of relaxation might be mediated through the blockade of receptor-operated calcium influx and L-type voltage-dependent calcium channels. The aqueous extract showed more significant in vitro vasodilatory effect than its fractions and 70% ethanol extract.

Functional involvement of L-type calcium channels and cyclic nucleotide-dependent pathways in cadmium-induced myometrial relaxation in rats.

Modulation of myometrial spontaneity by cadmium (Cd) and its regulatory pathways was studied in rat uterus in the absence and presence of blockers of different signaling pathways. Isometric tension in myometrial strips, under a resting tension of 1 g, mounted in organ bath containing Ringer-Locke solution (RLS) continuously aerated with carbogen, was measured using data acquisition system-based physiograph and Lab Chart Pro V7.3.7 software. Mean integral tension was measured for 8 min. Cd (1 nM-0.1 mM) not only produced concentration-dependent inhibitory effect on rat myometrium but it (10 µM) also significantly ( p < 0.05) inhibited calcium chloride and BAY K-8644-induced myometrial contraction. Glybenclamide (10 µM), 4-aminopyridine (1 mM), and propranolol (10 µM) failed to significantly attenuate Cd-induced inhibitory responses, while L-NAME (0.1 mM), 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 25 µM), and 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22536; 1 µM) significantly ( p < 0.05) produced inhibitory effects on Cd-induced myometrial relaxation. Phenylephrine (1 nM-10 µM) and salbutamol (0.01 nM-0.1 µM)-induced relaxant effects on rat myometrium were significantly potentiated by 10 µM Cd. Thus based on the results of present functional study, it may be inferred that inhibitory effects of Cd on rat myometrium are mediated through blockade of L-type calcium channels and activation of NOS-NO-sGC and/or AC-cAMP pathways.

Massive Overdose of Calcium Channel Antagonist and Successful Management: A Case Report and Review of Management

Calcium channel blockers (CCBs) toxicity is one of the most lethal drug overdoses encountered in the emergency department (ED). Nondihydropyridines (Verapamil and Diltiazem) are more lethal in overdose compared to dihydropyridines. The toxicity of these drugs is an extension of their therapeutic effect resulting from blockade of Ltype calcium channels in smooth muscle cells, myocardial cells, and beta cells of the pancreas. Significant overdoses can present with bradycardia, hypotension, cardiac arrest, hyperglycemia, metabolic acidosis and shock that can result in death. There have been many reported cases of Diltiazem toxicity treated with what would be considered standard approaches to treatment. However, very little has been reported on massive overdoses with Diltiazem and successful management of such cases. Here, we report on a young patient who self reportedly overdosed on two bottles of Diltiazem (approximately 60 pills). Initially, she was asymptomatic but shortly after her presentation, she became hemodynamically unstable. In this case report we discuss how we successfully managed the patient and give recommendations for management of such massive lethal overdoses.