Potent Calcium Channel Blocker Research Articles

Development of Physiologically Based Biopharmaceutical Model (PBBM) for Felodipine Prolonged-Release Tablet as useful tool for prediction of formulation.

Physiologically Based Biopharmaceutical Models (PBBMs) are advanced tools that integrate physiological parameters with drug-specific properties to simulate drug behavior in vivo. In this study, we present the development of a PBBM specifically tailored for felodipine prolonged-release (PR) tablet formulations. Felodipine, a potent calcium channel blocker, is widely used for the treatment of hypertension and angina pectoris. Prolonged-release formulations aim to provide controlled drug release, ensuring sustained therapeutic effect with reduced dosing frequency and minimized adverse effects. Our PBBM incorporates key physiological processes such as gastrointestinal transit, drug dissolution, absorption, distribution, metabolism, and elimination. Data from in vitro dissolution studies, preclinical pharmacokinetics, and clinical observations are integrated to parameterize the model accurately. Special attention is given to the physicochemical properties of felodipine and the release characteristics of the PR tablet formulation. Validation of the PBBM is conducted against clinical pharmacokinetic data obtained from bioequivalence studies and population pharmacokinetic analyses of felodipine PR tablets. The model may demonstrate excellent predictive performance, accurately capturing plasma concentration-time profiles across different dosing regimens and patient populations. The developed PBBM provides valuable insights into the biopharmaceutical behavior of felodipine PR tablets, facilitating rational formulation design, dosage regimen optimization, and therapeutic individualization. It serves as a powerful tool for drug developers, regulatory agencies, and clinicians to enhance the efficiency and effectiveness of drug development and clinical pharmacotherapy

Revolutionizing Drug Delivery: Nicardipine Nanosuspension Formulation and In-Vitro Evaluation

Nicardipine hydrochloride, is a potent calcium channel blocker, is commonly used in the management of hypertension and angina. It is a BCS class II drug which has low aqueous solubility and high permeability. In the present study, an attempt was made to formulate and evaluate nanosuspension of Nicardipine hydrochloride using different stabilizers, namely Tween 80, PVP K30, Poloxamer 188 by using Nanoprecipitation method with the objective to improve solubility and enhance dissolution of Nicardipine hydrochloride. Prepared nanosuspensions were evaluated for drug-excipient compatibility, particle size, PDI (Polydispersity Index), Zeta potential, Drug content, Saturation solubility, In-vitro release study, Scanning electron microscopy (SEM). FTIR (Fourier Transform Infrared Spectroscopy) studies revealed the compatibility of the drug with excipients. Nanosuspension (F3), which had the lowest particle size and the highest % Drug Release, was selected as the optimum formulation. It showed the droplet size, PDI, ZP,% Drug content and %Drug release of 150.4 nm,0.243, -30.6 mV,95.52%,91.24%. Kinetic release profiles of the NS F3 revealed that it followed First order kinetics. This study showed the ability of nanosuspension system in improving the solubility and drug release of Nicardipine.
 Keywords: Nicardipine, Nanosuspension, Solubility, % Drug Release, % Drug content, Scanning electron microscopy.

Formulation development and in vitro evaluation of bilayer tablets Nicardipine

The present work aims to develop a stable and optimized bilayer dosage form containing immediate release &extended release drug Nicardapine as an extended-release dosage form. A potent calcium channel blocker with marked vasodilator action. It has antihypertensive properties and is effective in the treatment of angina and coronary spasms without showing cardio depressant effects. It has also been used in the treatment of asthma and enhances the action of specific antineoplastic agents. It has a plasma half-life of about (8.6h) and bioavailability is 15-45% orally. For the formulation of Bilayered tablets polymers such as Ethylcellulose, Sodium CMC, CCS, SSG, Magnesium stearate, Talc, PVP-K30, and MCC. Fourier transform Infrared spectroscopy confirmed the absence of any drug/ polymers/ excipients interactions. Preformulation studies were carried out to optimize the ratios required for various Ethylcellulose, Sodium CMC, CCS, SSG, MCC, and PVP-K30. Based on various evaluation parameters formulation M6 (IR) & M6F3 (SR) were selected as optimized formulation. It was observed that Formulations M6 (IR) & M6F3 (SR) gave maximum drug release within time. All formulations were subjected for drug release kinetics studies viz. Zero-order, First order, Higuchi matrix, Peppasmodel equations, and the formulations of floating sustained-release formulations followed the zero-order release with non-fickian diffusion mechanism. Thus conclusion can be made that a stable dosage form can be developed for Nicardapine as immediate release & sustained release by Bilayered tablets.

Tetrandrine, a Potent Antifungal Agent, Inhibits Mycelial Growth and Virulence of Botrytis cinerea.

Tetrandrine (TET) is a potent calcium channel blocker used to treat hypertension and inflammation. Currently, TET is predominantly used to treat a variety of human diseases, and there is little information regarding the use of TET against plant pathogens. In this study, we explored the antifungal activity of TET on a plant pathogen, Botrytis cinerea. We show that administration of low concentrations of TET effectively inhibited hyphal growth of fungus grown on potato dextrose agarose and decreased the virulence of B. cinerea in tomato plants. Real-time PCR revealed that the expression of drug efflux pump-related genes (alcohol dehydrogenase 1, multidrug/pheromone exporter, pleiotropic drug resistance protein 1, and synaptic vesicle transporter) were downregulated in the presence of TET. Finally, we show that TET acts synergistically with iprodione, resulting in increased inhibition of B. cinerea both invitro and invivo. These results indicate that TET might act as an effective antifungal agent in reducing gray mold disease.

Nilvadipine suppresses inflammation via inhibition of P-SYK and restores spatial memory deficits in a mouse model of repetitive mild TBI

Repeated exposure to mild TBI (mTBI) has been linked to an increased risk of Alzheimer’s disease (AD), chronic traumatic encephalopathy (CTE) and other neurodegenerative diseases. Some pathological features typically observed in AD have been found in postmortem brains of TBI and CTE, hence treatments tested for AD have a potential to be effective against r-mTBI outcomes. Neuroinflammation may present a possible answer due to its central role both in acute brain injury and in chronic degenerative-like disorders. Our previous studies have shown that drug nilvadipine, acting as an inhibitor of spleen tyrosine kinase (SYK), is effective at reducing inflammation, tau hyperphosphorylation and amyloid production in AD mouse models. To demonstrate the effect of nilvadipine in the absence of age-related variables, we introduced the same treatment to young r-mTBI mice. We further investigate therapeutic mechanisms of nilvadipine using its racemic properties. Both enantiomers, (+)-nilvadipine and (−)-nilvadipine, can lower SYK activity, whereas (+)-nilvadipine is also a potent L-type calcium channel blocker (CCB) and shown to be anti-hypertensive. All r-mTBI mice exhibited increased neuroinflammation and impaired cognitive performance and motor functions. Treatment with racemic nilvadipine mitigated the TBI-induced inflammatory response and significantly improved spatial memory, whereas (−)-enantiomer decreased microgliosis and improved spatial memory but failed to reduce the astroglial response to as much as the racemate. These results suggest the therapeutic potential of SYK inhibition that is enhanced when combined with the CCB effect, which indicate a therapeutic advantage of multi-action drugs for r-mTBI.

Formulation of Polymeric Nanoparticles of Lercanidipine by Two Bottom Down Techniques Optimized by Design of Experiment

Lercanidipine has found to be effective in lowering blood pressure among the potent calcium channel blockers, through its action on L- type calcium channels. However, the major disadvantage associated with Lercanidipine is, it is a BCS class II drug having low solubility bioavailability is around 10% through oral route due of extensive first pass metabolism. The present study is aimed to prepare and evaluate polymeric nanoparticles of Lercanidipine using a combination of two bottom down techniques, High speed homogenizer and Probe sonication. Preformulation studies like, DSC, FTIR using surfactants such as Tween 80, Sodium Lauryl sulphate, Polyvinyl Alcohol, singely and in combination were used. A full factorial method was utilized to study the effect of various factors such as surfactant concentration, homogenization speed, sonication amplitude and sonication time on Lercanidipine nanoparticles in two levels. Optimized nanoparticles (with PVA as surfactant) showed an average particle size of 141 nm, PDI 0.248 and zeta potential +6.46. Formulation was further optimized using Design Expert 10 software. Optimized formulation was found to be stable during 3 months stability studies as per ICH guidelines.

Synthesis and cytotoxic effects of 2-thio-3,4-dihydroquinazoline derivatives as novel T-type calcium channel blockers

In our previous work, a series of 2-amino-3,4-dihydroquinazoline derivativesusing an electron acceptor group was reported to be potent T-type calcium channel blockers and exhibit strong cytotoxic effects against various cancerous cell lines. To investigate the role of the guanidine moiety in the 2-amino-3,4-dihydroquinazoline scaffold as a pharmacophore for dual biological activity, a new series of 2-thio-3,4-dihydroquniazoline derivatives using an electron donor group at the C2-position was synthesized and evaluated for T-type calcium channel blocking activity and cytotoxic effects against two human cancerous cell lines (lung cancer A549 and colon cancer HCT-116). Among them, compound 6g showed potent inhibition of Cav3.2 currents (83% inhibition) at 10 µM concentrations. The compound also exhibited IC50 values of 5.0 and 6.4 µM against A549 and HCT-116 cell lines, respectively, which are comparable to the parental lead compound KYS05090. These results indicate that the isothiourea moiety similar to the guanidine moiety of 2-amino-3,4-dihydroquinazoline derivatives may be an essential pharmacophore for the desired biological activities. Therefore, our preliminary work can provide the opportunity to expand a chemical repertoire to improve affinity and selectivity for T-type calcium channels.

Synthesis, structural characterization and density functional studies of ethyl 4-(biphenyl-4-yl)-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate A non-merohedral twinned structure

1,4-Dihydropyridine (1,4-DHP) derivatives have the reducing effect of extracellular Ca2+ ions influx on the L-type calcium channel. Because of this effect many 1,4-DHP derivatives are potent calcium channel blockers and antihypertensive agents. The biphenyl group is present in the structures of the most biologically active compounds and thus is an important group. By introducing this moiety into the structure of various compounds, active compounds are obtained. Thus, pharmacologically active structures can be condensed with the biphenyl structure to achieve novel biologically active compounds or compounds with increased activity. In this study, to achieve an active calcium channel blocker compound, the biphenyl group was introduced into the 1,4-DHP structure. The structure of the compound is proved by IR, 1H NMR, Mass spectroscopy, X-ray crystallography and elemental analysis. The cytotoxic activity assays have continued and positive results have been obtained. The phenyl rings [C16–C21 and C22–C27] make dihedral angles of 84.4 (1) and 87.5 (1)°, respectively, with the 1,4-dihydropyridine ring [N1/C1/C4–C9]. In the crystal, adjacent molecules are linked by NH … O and CH … O hydrogen bonds into chains parallel to [010].

Macrocyclic Antimicrobial Peptides Engineered from ω-Conotoxin.

The potent calcium channel blocker ω-conotoxin MVIIA is a linear cystine-knot peptide with multiple basic amino acids at both termini. This work shows that macrocyclization of MVIIA linking two positive-charge terminal clusters as a contiguous segment converts a conotoxin into an antimicrobial peptide. In addition, conversion of disulfide bonds to amino butyric acids improved the antimicrobial activity of the cyclic analogs. Ten macrocyclic analogs, with or without disulfide bonds, were prepared by both Boc and Fmoc chemistry using native chemical ligation. All cyclic analogs were active against selected Gram-positive and Gram-negative bacteria with minimal inhibitory concentrations in a low μM range. In contrast, MVIIA and its linear analog were inactive at concentrations up to 0.5 mM. The cyclic analogs also showed 2 to 3-fold improved chemotactic activity against human monocytes THP-1 compared with MVIIA. Reduction of molecular stability against thermal and acid treatment due to the reduced number of disulfide crosslinks can be partly restored by backbone cyclization. Together, these results show that macrocyclization and side chain modification of a linear conopeptide lead to a gain-of-function, which brings a new perspective in designing and engineering of peptidyl therapeutics.

Preparation, Antiepileptic Activity, and Cardiovascular Safety of Dihydropyrazoles as Brain-Penetrant T-Type Calcium Channel Blockers.

A series of dihydropyrazole derivatives was developed as potent, selective, and brain-penetrating T-type calcium channel blockers. An optimized derivative, compound 6c, was advanced to in vivo studies, where it demonstrated efficacy in the WAG/Rij rat model of generalized nonconvulsive, absence-like epilepsy. Compound 6c was not efficacious in the basolateral amygdala kindling rat model of temporal lobe epilepsy, and it led to prolongation of the PR interval in ECG recordings in rodents.

Blocking of T-Type Calcium Channels by TTA-A2 Reveals a Conservative Binding Site for State-Dependent Antagonists

T-type calcium channels, or CaV3 channels, are involved in several cell functions, and they can generate low-threshold spikes that lead to burst firing and oscillatory behavior in various types of neurons. In addition, CaV3 channels are also implicated in a number of pathophysiological processes such as epilepsy, sleep disorders, hypertension, neuropathic pain and cancer. However, until recently there were no potent and selective antagonists of CaV3 channels that facilitate further investigation of T-type channel function in neurological diseases and to validate these channels as efficient drug targets. Recently, a series of potent and selective T-type calcium channel blockers (T-type antagonists or TTAs) have been reported in several studies. Here, we describe the identification of one aminoacid that is determinant for the molecular coupling of TTA-A2 ([2-(4-cyclopropylphenyl)-N-((1R)-1-{5-[(2,2,2-trifluoroethyl)oxo]pyridin-2-yl}ethyl)acetamide]) on the CaV3.1 recombinant human T-type calcium channel. By using a combination of molecular modeling, docking studies, mutagenesis and patch-clamp experiments of CaV3.1 channels expressed in HEK-293 cells, we have collected experimental evidence that supports the existence of a conservative binding site for TTA-A2 and state-dependent antagonists similar to TTA-A2, e.g., mibefradil. Blocking potency of TTA-A2 was reduced by two thirds in CaV3.1 mutants, where the identified aminoacid was replaced for alanine, proline, or arginine, among others. Sequence alignment of the three human CaV3 channels suggest that the binding site is conserved in the CaV3 subfamily, but not in the L-type CaV1.2 channel. In addition, our data also provides further evidence that TTA-Q4, a positive allosteric modulator of TTA-A2 functional inhibition, does not share the same binding site with the latter. Our results contribute to the knowledge for the rational design of T-type channel antagonists based on the structure of the TTA-A2 binding site.Supported by CONACYT-MEXICO 167790.

Roles of lymphocyte kv1.3-channels in the pathogenesis of renal diseases and novel therapeutic implications of targeting the channels.

Delayed rectifier K+-channels (Kv1.3) are predominantly expressed in T lymphocytes. Based on patch-clamp studies, the channels play crucial roles in facilitating the calcium influx necessary to trigger lymphocyte activation and proliferation. Using selective channel inhibitors in experimental animal models, in vivo studies then revealed the clinically relevant relationship between the channel expression and the pathogenesis of autoimmune diseases. In renal diseases, in which “chronic inflammation” or “the overstimulation of cellular immunity” is responsible for the pathogenesis, the overexpression of Kv1.3-channels in lymphocytes promotes their cellular proliferation and thus contributes to the progression of tubulointerstitial fibrosis. We recently demonstrated that benidipine, a potent dihydropyridine calcium channel blocker, which also strongly and persistently inhibits the lymphocyte Kv1.3-channel currents, suppressed the proliferation of kidney lymphocytes and actually ameliorated the progression of renal fibrosis. Based on the recent in vitro evidence that revealed the pharmacological properties of the channels, the most recent studies have revealed novel therapeutic implications of targeting the lymphocyte Kv1.3-channels for the treatment of renal diseases.

Discovery of novel tetrahydroisoquinoline derivatives as orally active N-type calcium channel blockers with high selectivity for hERG potassium channels

N-type calcium channels represent a promising target for the treatment of neuropathic pain. The selective N-type calcium channel blocker ziconotide ameliorates severe chronic pain but has a narrow therapeutic window and requires intrathecal administration. We identified tetrahydroisoquinoline derivative 1a as a novel potent N-type calcium channel blocker. However, this compound also exhibited potent inhibitory activity against hERG channels. Structural optimizations led to identification of (1S)-(1-cyclohexyl-3,4-dihydroisoquinolin-2(1H)-yl)-2-{[(1-hydroxycyclohexyl)methyl]amino}ethanone ((S)-1h), which exhibited high selectivity for hERG channels while retaining potency for N-type calcium channel inhibition. (S)-1h went on to demonstrate in vivo efficacy as an orally available N-type calcium channel blocker in a rat spinal nerve ligation model of neuropathic pain.

Thalamocortical neurons display suppressed burst-firing due to an enhanced Ih current in a genetic model of absence epilepsy.

Burst-firing in distinct subsets of thalamic relay (TR) neurons is thought to be a key requirement for the propagation of absence seizures. However, in the well-regarded Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model as yet there has been no link described between burst-firing in TR neurons and spike-and-wave discharges (SWDs). GAERS ventrobasal (VB) neurons are a specific subset of TR neurons that do not normally display burst-firing during absence seizures in the GAERS model, and here, we assessed the underlying relationship of VB burst-firing with Ih and T-type calcium currents between GAERS and non-epileptic control (NEC) animals. In response to 200-ms hyperpolarizing current injections, adult epileptic but not pre-epileptic GAERS VB neurons displayed suppressed burst-firing compared to NEC. In response to longer duration 1,000-ms hyperpolarizing current injections, both pre-epileptic and epileptic GAERS VB neurons required significantly more hyperpolarizing current injection to burst-fire than those of NEC animals. The current density of the Hyperpolarization and Cyclic Nucleotide-activated (HCN) current (Ih) was found to be increased in GAERS VB neurons, and the blockade of Ih relieved the suppressed burst-firing in both pre-epileptic P15–P20 and adult animals. In support, levels of HCN-1 and HCN-3 isoform channel proteins were increased in GAERS VB thalamic tissue. T-type calcium channel whole-cell currents were found to be decreased in P7–P9 GAERS VB neurons, and also noted was a decrease in CaV3.1 mRNA and protein levels in adults. Z944, a potent T-type calcium channel blocker with anti-epileptic properties, completely abolished hyperpolarization-induced VB burst-firing in both NEC and GAERS VB neurons.

Decreased L-type calcium current in antral smooth muscle cells of STZ-induced diabetic rats.

Diabetic gastroparesis (delayed gastric emptying) is associated with antral hypomotility. L-type Ca(2+) channels play an important role in generation of action potentials and activation of contractions. This study was designed to investigate if the function of the L-type Ca(2+) channels of antral circular smooth muscle cells (SMCs) is impaired in streptozotocin (STZ)-induced diabetic rats. Eight weeks after the injection of STZ or vehicle, whole-cell patch clamp was used to record Ca(2+) currents, and isometric tension recording was used to measure Ca(2+) influx-induced contractions in circular muscle strips. Solid gastric emptying was measured in diabetic and control rats. Protein expression of Ca(2+) αlC-subunit in antral smooth muscles was compared between diabetic and control rats. (1) Solid gastric emptying, independent of age or bodyweight, was slower in the diabetic rats, even after acute correction of hyperglycemia. (2) Verapamil, a potent calcium channel blocker, dose dependently reduced solid gastric emptying in normal rats. (3) Current density of L-type Ca(2+) channel at 10 mV in antral circular SMCs was significantly decreased in the diabetic rats (-9.8 ± 0.7 pA/pF vs -15.9 ± 1.0 pA/pF in control, p < 0.001). However, protein expression of the Ca(2+) channel in antral muscles did not differ between diabetic and control rats. (4) Contractile responses to 1 and 3 mM [Ca(2+) ] were significantly reduced in the diabetic antral circular muscle strips, indicative of reduced Ca(2+) influx. These data suggested that the decreased L-type Ca(2+) current in antral SMCs may contribute to antral hypomotility in STZ-induced diabetic rats.

Development of isradipine loaded self-nano emulsifying powders for improved oral delivery: in vitro and in vivo evaluation

Isradipine (ISR) is a potent calcium channel blocker with low oral bioavailability due to low aqueous solubility, extensive first-pass metabolism and P-glycoprotein (P-gp)-mediated efflux transport. In the present investigation, an attempt was made to develop isradipine-loaded self-nano emulsifying powders (SNEP) for improved oral delivery. The liquid self-nano emulsifying formulations (L-SNEF/SNEF) of isradipine were developed using vehicles with highest drug solubility, i.e. Labrafil® M 2125 CS as oil phase, Capmul® MCM L8 and Cremophor® EL as surfactant/co-surfactant mixture. The developed formulations revealed desirable characteristics of self-emulsifying system such as nano-size globules ranging from 32.7 to 40.2 nm, rapid emulsification (around 60 s), thermodynamic stability and robustness to dilution. The optimized stable self-nano emulsifying formulation (SNEF2) was transformed into SNEP using Neusilin US2 (SNEPN) as adsorbent inert carrier, which exhibited similar characteristics of liquid SNEF. The solid state characterization of SNEPN by Fourier transform infrared spectroscopy, differential scanning calorimetry, powder X-ray diffraction and scanning electron microscopic studies shown transformation of crystalline drug into amorphous form or molecular state without any chemical interaction. The in vitro dissolution of SNEPN compared to pure drug was indicated by 18-fold increased drug release within 5 min. In vivo pharmacokinetic studies in Wistar rats showed significant improvement of oral bioavailability of isradipine from SNEPN with 3- and 2.5-fold increments in peak drug concentration (Cmax), area under curve (AUC0–∞) compared to pure isradipine. In conclusion, these results signify the improved oral delivery of isradipine from developed SNEP.

Synthesis and biological evaluation of 1-(isoxazol-5-ylmethylaminoethyl)-4-phenyl tetrahydropyridine and piperidine derivatives as potent T-type calcium channel blockers with antinociceptive effect in a neuropathic pain model

New tetrahydropyridinyl and piperidinyl ethylamine derivatives were designed with hypothetical mapping on pharmacophore model generated from ligand-based virtual screening. The designed compounds were synthesized, and their inhibitory activities on T-type calcium channel were assayed using FDSS and patch-clamp assay. Among them, compounds 7b and 10b showed potent T-type calcium current blocking activity against Cav3.1 (α1G) and Cav3.2 (α1H) channel simultaneously. With hERG and pharmacokinetics studies, compounds 7b and 10b were evaluated for the antinociceptive effect on rat model of neuropathic pain. They were significantly effective in decreasing the pain responses to mechanical and cold allodynia induced by spinal nerve ligation. These results suggest that modulation of α1G and α1H subtype T-type calcium channels may provide a promising approach for the treatment of neuropathic pain.

Modular, efficient synthesis of asymmetrically substituted piperazine scaffolds as potent calcium channel blockers

A novel approach to the synthesis of substituted piperazines and their investigation as N-type calcium channel blockers is presented. A common scaffold exhibiting high activity as N-type blockers is N-substituted piperazine. Using recently developed titanium and zirconium catalysts, we describe the efficient and modular synthesis of 2,5-asymmetrically disubstituted piperazines from simple amines and alkynes. The method requires only three isolation/purification protocols and no protection/deprotection steps for the diastereoselective synthesis of 2,5-dialkylated piperazines in moderate to high yield. Screening of the synthesized piperazines for N-type channel blocking activity and selectivity shows the highest activity for a compound with a benzhydryl group on the nitrogen (position 1) and an unprotected alcohol-functionalized side chain.

In vitro activity of verapamil alone and in combination with fluconazole or tunicamycin against Candida albicans biofilms

Calcium channels and pumps play important roles in morphogenesis, stress response and virulence in Candida albicans. We hypothesised that verapamil, a potent calcium channel blocker, may display an inhibitory effect on C. albicans biofilms. To test this hypothesis, the in vitro activity of verapamil was evaluated alone and in combination with fluconazole or tunicamycin against C. albicans biofilms using a 96-well microtitre plate model. As expected, verapamil exerted inhibitory activity against C. albicans biofilms. The combinations of verapamil/fluconazole and verapamil/tunicamycin yielded synergistic effects on biofilm formation and on pre-formed biofilms. Furthermore, verapamil alone or in combination with fluconazole or tunicamycin led to a significant decrease in the transcription level of ALS3, essential for biofilm development. Therefore, verapamil may be a potential agent to enhance the effect of antifungal drugs against C. albicans biofilms.

Selective inhibitory action of Biginelli-type dihydropyrimidines on depolarization-induced arterial smooth muscle contraction

Dihydropyridine calcium channel blockers have some disadvantages such as light sensitivity and relatively short plasma half-lives. Stability of dihydropyrimidines analogues could be of advantage, yet they remain less well characterized. We aimed to test four newly synthesized Biginelli-type dihydropyrimidines for their calcium channel blocking activity on rat isolated aorta. Dihydropyrimidines (compounds A-D) were prepared by the Biginelli-like three-component condensation of benzaldehydes with urea/thiourea and dimethyl or diethyl acetone-1,3-dicarboxylate, and their physicochemical properties and effects on depolarization-induced and noradrenaline-induced contractions of rat isolated aorta were evaluated. Dihydropyrimidines A and C blocked KCl-induced contraction only weakly (-log(IC50)=5.03 and 3.73, respectively), while dihydropyrimidine D (-log(IC50)=7.03) was almost as potent as nifedipine (-log(IC50)=8.14). Washout experiments revealed that dihydropyrimidine D may bind strongly to the L-type calcium channel or remains bound to membrane. All tested dihydropyrimidines only marginally inhibited noradrenaline-induced contractions of rat isolated aorta (20% reduction of noradrenaline E(max) ), indicating a more selective action on L-type calcium channel than nifedipine with 75% inhibition of noradrenaline E(max) at 10(-4) m nifedipine). Compounds A and, particularly, D are potent calcium channel blockers in vitro, with a better selectivity in inhibiting depolarization-induced arterial smooth muscle contraction than nifedipine.