Calcium Antagonist Flunarizine Research Articles

Vorbeugung und Akutbehandlung der Migräne

The treatment of migraine consists of the acute treatment of the migraine attack and prophylactic measures for either pharmacological or non-pharmacological management. Since the retreat of the ergotamines one can only choose between one of the well-established analgesics and one of seven triptans for the treatment of the migraine attack. Although neither a new triptan nor an innovative new application form has been introduced, the year 2006 will be remembered as the year when the first triptan (naratriptan) was released as a prescription-free over-the-counter drug and when the first sumatriptan generics were marketed in Germany. In addition to the beta-blockers metoprolol and propranolol and the calcium antagonist flunarizine two antiepileptic drugs, topiramate and valproic acid, have been rated as first-line prophylactic drugs in Germany. Due to an extensive and successful study program topiramate has been officially approved in Germany.

Perinatal brain damage—from pathophysiology to prevention

Children undergoing perinatal brain injury often suffer from the dramatic consequences of this misfortune for the rest of their lives. Despite the severe clinical and socio-economic significance, no effective clinical strategies have yet been developed to counteract this condition. This review describes the pathophysiological mechanisms that are implicated in perinatal brain injury. These include the acute breakdown of neuronal membrane potential followed by the release of excitatory amino acids such as glutamate and aspartate. Glutamate binds to postsynaptically located glutamate receptors that regulate calcium channels. The resulting calcium influx activates proteases, lipases and endonucleases which in turn destroy the cellular skeleton. The acute lack of cellular energy during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to preischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. A second wave of neuronal cell damage occurs during the reperfusion phase induced by the postischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Clinical studies have shown that intrauterine infection increases the risk of periventricular white matter damage especially in the immature fetus. This damage may be mediated by cardiovascular effects of endotoxins leading to cerebral hypoperfusion and by activation of apoptotic pathways in oligodendrocyte progenitors through the release of pro-inflammatory cytokines. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies which have been shown to be neuroprotective in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of postischemic induction of mild cerebral hypothermia, the application of the calcium-antagonist flunarizine and the administration of magnesium.

Perinatal Brain Damage: Underlying Mechanisms and Neuroprotective Strategies

Children who suffer from perinatal brain injury often deal with the dramatic consequences of this misfortune for the rest of their lives. Despite the severe clinical and socioeconomic significance, no effective clinical strategies have yet been developed to counteract this condition. As shown in recent studies, perinatal brain injury is usually brought about by cerebral ischemia, cerebral hemorrhage, or an ascending intrauterine infection. This review focuses on the pathophysiologic pathways activated by these insults and describes neuroprotective strategies that can be derived from these mechanisms. Fetal cerebral ischemia causes an acute breakdown of neuronal membrane potential followed by the release of excitatory amino acids such as glutamate and aspartate. Glutamate binds to postsynaptically located glutamate receptors that regulate calcium channels. The resulting calcium influx activates proteases, lipases, and endonucleases, which in turn destroy the cellular skeleton. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the postischemic release of oxygen radicals, synthesis of nitric oxide, inflammatory reactions, and an imbalance between the excitatory and inhibitory neurotransmitter systems. Furthermore, secondary neuronal cell damage may be brought about in part by induction of a cellular suicide program known as apoptosis. Recent studies have shown that inflammatory reactions not only aggravate secondary neuronal damage after cerebral ischemia, but may also injure the immature brain directly. This damage may be mediated by cardiovascular effects of endotoxins leading to cerebral hypoperfusion and by activation of apoptotic pathways in oligodendrocyte progenitors through the release of proinflammatory cytokines. Periventricular or intraventricular hemorrhage (PIVH) is a typical lesion of the immature brain. The inability of preterm fetuses to redistribute cardiac output in favor of the central organs and their lack of cerebral autoregulation may cause significant fluctuations in cerebral blood flow when oxygen is in short supply. Disruption of the thin-walled blood vessels in the germinal matrix with subsequent cerebral hemorrhage is often the inevitable result and is at times associated with cerebral hemorrhagic infarction. Knowledge of these pathophysiologic mechanisms has enabled scientists to develop new therapeutic strategies, which have been shown to be neuroprotective in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of postischemic induction of cerebral hypothermia, the application of the calcium-antagonist flunarizine, and the administration of magnesium.

Reversal by flunarizine of the decrease in hippocampal acetylcholine release in pentylenetetrazole-kindled rats

The aim of our study was to evaluate the effect of the non-selective calcium antagonist flunarizine on hippocampal acetylcholine (ACh) release with the microdialysis technique in freely moving rats after long-term concomitant administration of pentylenetetrazole (PTZ) in comparison with rats treated long-term with PTZ (kindled animals). The basal extracellular concentration of ACh in the hippocampus of rats treated with PTZ alone was significantly reduced relative to that of vehicle-treated rats (2.04 ± 0.2 vs 3.94 ± 0.3 pmol per 20-min sample; P < 0.01). Administration of flunarizine (7.5 mg/kg i.p.) before each PTZ injection prevented this decrease in basal ACh output (3.75 ± 0.4 pmol per 20-min sample). On the contrary, the expression of PTZ-induced kindling was not prevented by administration of flunarizine. The specific antagonistic effect of flunarizine on the kindling-induced decrease in hippocampal ACh release is shared by the selective antagonist of the L-type calcium channel, nifedipine, but not by the dopamine D 2 antagonist, (−)-sulpiride, suggesting that the decrease in Ca 2+ overload by a blockade of the L-type calcium channel may be responsible for the protective action on cholinergic neurons exerted by flunarizine. These data also suggest a potential therapeutic role for flunarizine in counteracting impairment of hippocampal cholinergic activity.

A practical guide to the management and prevention of migraine.

Migraine is a paroxysmal disorder with attacks of headache, nausea, vomiting, photo- and phonophobia and malaise. Mild migraine attacks are treated with antiemetics followed by analgesics such as aspirin (acetylsalicylic acid), paracetamol (acetaminophen) or nonsteroidal anti-inflammatory drugs (NSAIDs). Moderate to severe attacks are treated by antiemetics combined with ergotamine or dihydroergotamine. Sumatriptan, a specific serotonin 5-HT1B/D receptor agonist, is used if attacks do not respond to ergotamine or if intolerable adverse effects occur. The new migraine drugs zolmitriptan, naratriptan, rizatriptan and eletriptan differ in their pharmacological profile from sumatriptan, but this translates into only minor differences in efficacy, headache recurrence and adverse effects. Migraine prophylaxis should be implemented when more than 3 attacks occur per month, if attacks do not respond to acute treatment or if the adverse effects of acute treatment are severe. Substances with proven efficacy include the beta-blockers metoprolol and propranolol and the calcium antagonist flunarizine. Drugs less effective or those with unpleasant adverse effects are the serotonin receptor antagonists (pizotifen, methysergide and lisuride), dihydroergotamine, cyclandelate, NSAIDs, valproic acid (sodium valproate) and amitriptyline. The efficacy of aspirin or magnesium is still under evaluation.

Determination of tumor-related factors of influence on the uptake of the monoclonal antibody 323/A3 in experimental human ovarian cancer

The epithelial glycoprotein 40 (EGP40) is an important target in the clinic for radioimmunolocalization and monoclonal antibody (MAb)-mediated therapy of cancer. We determined which tumor-related factors (including antigen distribution and density, vascularization and perfusion) were involved in the uptake of the anti-EGP40 MAb 323/A3 in 4 different human ovarian cancer xenografts grown s.c. in nude mice. The reactivity pattern of 323/A3 in all xenografts in vitro was similar and showed a strong and homogeneous distribution of the EGP40 antigen. FMa xenografts, however, showed the highest uptake of 323/A3 in vivo, which was 5.5-, 6.2- and 10.0-fold higher than that in OVCAR-3, Ov.Pe and Ov.Sh xenografts, respectively. FMa xenografts contained 2.1- to 3.5-fold more antigen per gram protein when compared with the antigen content of the other xenografts. FMa and Ov.Sh xenografts demonstrated a better vascularization pattern, whereas Ov.Pe and OVCAR-3 xenografts were moderately to poorly vascularized. FMa xenografts were also better perfused, as was shown by a 1.6- to 1.8-fold higher uptake of the (99m)Tc-labeled blood flow marker hexamethylpropyleneamine oxime (HMPAO). The tumor uptake of the non-specific MAb E48 was 2.2- to 11.2-fold lower when compared with that of 323/A3, but the sequence of uptake was similar (FMa > OVCAR-3 = Ov.Pe > Ov.Sh), indicating the lowest extravasation of MAbs in Ov.Sh xenograft tissue. Since both the antigen content and the perfusion appeared to be important factors of influence on the tumor uptake of 323/A3, attempts were made to manipulate these determinants to improve the tumor uptake. Neither gamma-interferon nor 5-fluorouracil were able to increase EGP40 expression in human ovarian cancer cells in vitro. Treatment of tumor-bearing mice with the calcium-antagonist flunarizine did not result in an improved perfusion, although a slight increase in the initial tumor uptake of 323/A3 was observed in Ov.Sh-bearing mice. Our results illustrate the relative contribution of various tumor-related factors that determine the usefulness of a MAb for imaging and therapy of cancer.

Determination of tumor‐related factors of influence on the uptake of the monoclonal antibody 323/A3 in experimental human ovarian cancer

The epithelial glycoprotein 40 (EGP40) is an important target in the clinic for radioimmunolocalization and monoclonal antibody (MAb)-mediated therapy of cancer. We determined which tumor-related factors (including antigen distribution and density, vascularization and perfusion) were involved in the uptake of the anti-EGP40 MAb 323/A3 in 4 different human ovarian cancer xenografts grown s.c. in nude mice. The reactivity pattern of 323/A3 in all xenografts in vitro was similar and showed a strong and homogeneous distribution of the EGP40 antigen. FMa xenografts, however, showed the highest uptake of 323/A3 in vivo, which was 5.5-, 6.2- and 10.0-fold higher than that in OVCAR-3, Ov.Pe and Ov.Sh xenografts, respectively. FMa xenografts contained 2.1- to 3.5-fold more antigen per gram protein when compared with the antigen content of the other xenografts. FMa and Ov.Sh xenografts demonstrated a better vascularization pattern, whereas Ov.Pe and OVCAR-3 xenografts were moderately to poorly vascularized. FMa xenografts were also better perfused, as was shown by a 1.6- to 1.8-fold higher uptake of the 99mTc-labeled blood flow marker hexamethylpropyleneamine oxime (HMPAO). The tumor uptake of the non-specific MAb E48 was 2.2- to 11.2-fold lower when compared with that of 323/A3, but the sequence of uptake was similar (FMa > OVCAR-3 = Ov.Pe > Ov.Sh), indicating the lowest extravasation of MAbs in Ov.Sh xenograft tissue. Since both the antigen content and the perfusion appeared to be important factors of influence on the tumor uptake of 323/A3, attempts were made to manipulate these determinants to improve the tumor uptake. Neither γ-interferon nor 5-fluorouracil were able to increase EGP40 expression in human ovarian cancer cells in vitro. Treatment of tumor-bearing mice with the calcium-antagonist flunarizine did not result in an improved perfusion, although a slight increase in the initial tumor uptake of 323/A3 was observed in Ov.Sh-bearing mice. Our results illustrate the relative contribution of various tumorrelated factors that determine the usefulness of a MAb for imaging and therapy of cancer. Int. J. Cancer 71:237–245, 1997. © 1997 Wiley-Liss, Inc.

Effect of dotarizine on CO2-dependent cerebrovascular reactivity.

Dotarizine is chemically related to calcium antagonist cinnarizine and flunarizine. The study presented investigates the influence of the drug on the diameter of cortical arteries and cerebral blood velocity measured in the MCA in two groups of anaesthetized cats. Changes of vessel diameter were measured indirectly using photographs of the cerebral cortex during experiments, and flow velocity was measured using transcranial Doppler sonography. Dotarizine was administrated by 20 minute intravenous infusion in a dose of 0.05 mg/kg/min. In the first group of animals the infusion was started during normoventilation, in the next group the infusion started during 30th minute of hyperventilation. The most conspicuous data were obtained in experiments conducted in hyperventilated animals where dotarizine abolished the vasoconstrictive effect of hyperventilation. The results suggest that dotarizine has a pronounced effect on basal as well as cortical arteries of the brain.

Poster 63: Inhibition of Deafferentation‐Induced Neuronal Death in the Cochlear Nucleus by the Calcium Antagonist Flunarizine

Poster 63: Inhibition of Deafferentation‐Induced Neuronal Death in the Cochlear Nucleus by the Calcium Antagonist Flunarizine

Synthesis of 7-benzylideneoctahydro-2H-pyrido[1,2-a]pyrazines, bicyclic analogues of the calcium antagonist flunarizine

The bicyclic amino ketone 4(2-benzyloctahydro-2H-pyrido[1,2-a]pyrazin-7-one) has been converted in four steps into the pharmacologically interesting (Z)- and (E)-7-benzylideneoctahydro-2H-pyrido[1,2-a]pyrazines 2a, b, bicyclic analogues of the calcium antagonist flunarizine 1. In the key step, olefination of the ketone group, the yield was highly improved (15–20%→82–85%) by using (a) the phosphonate anion instead of the Wittig reagent and (b) the solvent 1,3-dimethylimidazolidin-2-one instead of tetrahydrofuran. Debenzylation and final substitution of the 2-amino group with (4-FCSH4)2CHCI gave the geometric isomers 2a(Z) and 2b(E) in 53% overall yield.

Gastric histamine content and ulcer formation in rats with ethanol-induced injury. Effects of cinnarizine and flunarizine

The effects of the calcium antagonists cinnarizine and flunarizine on gastric histamine content and ulcer formation in rats with ethanol-induced injury were studied. Gastric ulcers were inflicted by oral application of 50% or 100% ethanol solution. Cinnarizine (20 mg/kg), flunarizine (10 mg/kg) and cimetidine (100 mg/kg) were administered orally 1 h before ethanol. Histamine was assayed fluorometrically. No effect of the tested drugs on 50% ethanol-induced gastric damage was observed. Cinnarizine and flunarizine inhibited 100% ethanol-induced lesion formation by 71% (p < 0.01) and 20% (p > 0.05), respectively. The inhibition exerted by cimetidine was 54% (p < 0.05). Gastric histamine content was not affected by 50% ethanol, while 100% ethanol decreased it two-fold. None of the tested drugs induced significant changes in gastric histamine levels. No correlation was obtained between the ulceroprotective effect of the used calcium antagonists and the gastric histamine content in ethanol-induced injury.

Reply to the Letter of H. J. Koch

In the investigation quoted by Dr. Koch1 radiosensitivity and local flow in experimental mouse sarcomas were improved by the calcium antagonist flunarizine. This result is not contradictory to our finding that dihydropyridine calcium antagonists such as nifedipine, nimodipine, nitrendipine, and isradipine and the benzothiazepine calcium antagonist, diltiazem, protect mice against lethal radiation (1, 2). Flunarizine, which is a piperazine calcium antagonist, did not display radioprotective effects in our work (1, 2), and neither did the phenylalkylamine calcium antagonist verapamil. It thus appears that radioprotection is not a general property of Ca2+ channel blockers, but that a certain degree of specificity within the class is needed. The evidence that radioprotective or radio-enhancing effects of calcium antagonists are connected to their effects on flow and thus tissue oxygenation does not appear too convincing for several reasons. If calcium antagonists were used as blood flow modifiers and their influence on the radiation response of experimental mouse tumors was studied (3), small doses of nifedipine and verapamil enhanced local flow and radiosensitivity, while large doses of these agents reduced flow and radiosensitivity. However, in our studies, verapamil at a large dose did not reduce radiosensitivity and nifedipine consistently provided radioprotection and failed to sensitize at the lowest dose tested. Flunarizine, which increased radiosensitivity over the whole dose range, afforded a small increase in flow at only one dose (3). Also, the observation that a large array of antihypertensive and vasodilation drugs did not affect the radiosensitivity of mice (1) does not make it possible to ascribe an important role to flow changes. A more direct effect on Ca2' channels or on the interaction of radiation with cells at the biochemical or biophysical level seems more appropriate for explaining radioprotection by calcium antagonists. While Dr. Koch mentions inhibitory effects of calcium antagonists on cell proliferation and multidrug resistance, evidence is also available indicating general cytoprotective properties of calcium antagonists, e.g., with reperfusion injury (4), ischemia (5, 6), toxicity of cytotoxic agents (7), and neurotoxic injuries (8, 9). Finally, it could be argued that in view of differences in radiation response between normal and tumor cells, results obtained with tumors may not necessarily apply to normal tissue. Dr. Koch also addresses the role of the solvent. Since nifedipine and nimodipine had to be applied in a vehicle containing DMSO and ethanol, the possible role of the solvent was investigated in our reports (1, 2). The radioprotection provided by calcium antagonist in the solvent was superior to the protection afforded by the solvent alone. Moreover, nitrendipine and isradipine, which were administered in vehicles displaying no radioprotection, namely distilled water or olive oil, provided significant radioprotection. Diltiazem protected markedly and was applied in a solvent which contained mannitol and distilled water, which have no adioprotective faculties.

Results of a prospective open study of therapy of sudden deafness with flunarizine

The treatment effect of the lipophilic calcium antagonist flunarizine on the recovery of sudden hearing loss was evaluated in a prospective phase-II study. Thirty-seven patients presenting with recent and sudden onset of unilateral sensorineural hearing loss were treated with 50 mg flunarizine intravenously for the first two days followed by 10 mg flunarizine orally for four weeks. Pure-tone audiometry was done before the beginning of the treatment and after one and four weeks. The absolute and relative hearing gains after one and four weeks were compared to those of 67 similar patients previously treated with saline infusions and placebo tablets in the same institutions during a double blind study (Probst et al. Acta Otolaryngol. 112 (1992) 435-443). The mean absolute hearing gains of the flunarizine group was 17 dB and 21 dB, after one and four weeks respectively (placebo group: 16 dB and 24 dB). The corresponding relative hearing gains (defined as absolute gain divided by initial hearing loss) were 35% and 43% for the flunarizine group and 33% and 42% for the placebo group. We conclude that flunarizine treatment does not improve the recovery of sudden hearing loss.

Binding of the calcium antagonist flunarizine to phosphatidylcholine bilayers: charge effects and thermodynamics

We have examined the partitioning/transfer of the Ca2+ antagonist flunarizine from the aqueous phase into phospholipid bilayers. We show that the binding of the cationic amphiphilic drug flunarizine to phospholipid bilayers displays traditional linear concentration-dependent characteristics once unmasked of electrostatic effects. The coefficient for the binding/partitioning of flunarizine to phosphatidylcholine was found to be 28700 M-1, supporting the notion that this drug may be particularly membrane-active. The thermodynamics of the partitioning/transfer process have also been studied using high-sensitivity titration calorimetry. Binding was found to be predominantly enthalpy-driven with only a small entropic contribution; delta H = -22.1 kJ.mol-1 (-5.3 kcal.mol-1) at 27 degrees C. This is in conflict with established ideas of entropy-driven partitioning of drugs into phospholipid membranes as a result of the 'hydrophobic effect'. The strong enthalpic nature of binding is interpreted as being indicative of strong lipophilic interactions between the drug and the phospholipid phase.

Efficacy of cerebroprotective substances in the management of functional disorders induced by the cytotoxic brain oedema-producing substance hexachlorophene

The hexachlorophene-induced cytotoxic brain oedema is used as experimental model of brain damage, suitable for testing cerebroprotective substances. It has clinical importance since many brain injuries are accompanied by an oedema. The primary target of the neurotoxin, hexachlorophene, is the neuronal cell membrane, but it also causes secondary effects including a disruption of myelin lamellae, increases in water and sodium content, decreases of potassium content, and vacuolation in the white matter. Rats received orally hexachlorophene 240 mg/kg a day for three weeks by liquid diet. The disruption of coordinative motor response, observed in a specially developed test, was used to characterise hexachlorophene-induced injuries in studies designed to evaluate the potential of cerebroprotective substances. Because of their membranotropic efficacy some nootropic substances with different modes of action were examined. The disturbance of coordinative motor response was restored significantly earlier than in spontaneous remission following administration of piracetam, pyritinol, methyl glucamine orotate, naftidrofuryl, and also under the influence of the calcium antagonists cinnarizine, flunarizine and nifedipine. These results support the therapeutic use of nootropic substances in the management of neurotoxic injuries and brain oedema.

Nimodipine and flunarizine in alcohol withdrawal: an open study

An open pilot study of the calcium antagonists nimodipine (240 mg/die p.o.) and flunarizine (20 mg/die p.o.) as a treatment in alcohol withdrawal was conducted. Two of the eight patients who received nimodipine and one of the eight patients who received flunarizine developed a confusional state preceded, in one of the patients with nimodipine and in the patient with flunarizine, by a generalized tonic-clonic seizure. The patients receiving flunarizine seemed to recover faster from the alcohol withdrawal syndrome than the patients receiving nimodipine. Given the limited capability of both drugs to prevent severe withdrawal symptoms at the doses tested, double-blind studies with these drugs, possibly with higher doses and i.v. administration should follow an add-on design.

The response of spontaneous and transplantable murine tumors to vasoactive agents measured by 31p magnetic resonance spectroscopy

31P magnetic resonance spectroscopy has been used to compare the effects of the vasoactive agents hydralazine and flunarizine on the oxygenation of the transplantable tumors, SCCVII/Ha and 16C, and a range of spontaneous mammary tumors arising in the breeding stock in the Genetics Division at the Radiobiology Unit. The vasodilator hydralazine, previously shown to increase the radiobiological hypoxic fraction of transplantable murine tumors, increased inorganic phosphate to total phosphate (Pi/total) in SCCVIVHa and 16C tumors. However, only two spontaneous tumors responded to this agent ( sol2 12 ). The calcium antagonist flunarizine, which sensitizes the SCCVH tumor to X rays, consistent with a reduction in hypoxic fraction, reduced Pi/total in this and the 16C tumor. Further, most spontaneous tumors tested ( 8 10 ) responded to this agent, as measured by a reduction in Pi/total. These results point to fundamental differences between transplantable and spontaneously arising tumors in mice in their response to vasoactive agents.

Calcium antagonist flunarizine hydrochloride affects striatal D2 dopamine receptors in the young adult and aged rat brain

The calcium (Ca) antagonist flunarizine hydrochloride (FNZ) has been reported to induce parkinsonism, especially in the elderly. The effects of FNZ on dopamine receptors in rat striatal membranes, especially in aged rats, were studied using radiolabeled receptor assay. Similar displacing potencies in [ 3H]spiperone bindings were exhibited for FNZ and the Ca antagonists verapamil and nicardipine. FNZ was found to directly and competitively effect D2 receptors (D2-Rs) as an antagonist, without effecting D1 receptors. Furthermore, the washing of preoccupied membranes revealed that FNZ has a long-acting potent effect on D2-Rs. The comparative study of FNZ and sulpiride in young-adult and aged rats showed that the effect of FNZ on D2-Rs was more marked in aged rats. These results might be related to FNZ-induced parkinsonism and its high incidence in the elderly.

Flunarizine attenuates cocaine-induced inhibition of A 9 dopaminergic neurons

The intravenous administration of cocaine (0.5–8 mg/kg) produced a dose-related inhibition of the firing rate of substantia nigra (A 9) dopaminergic (DA) neurons. Pretreatment with the calcium antagonist flunarizine (5 mg/kg i.v.) prevented cocaine-induced effects but failed to antagonize the inhibition of firing induced by a low dose of apomorphine (10μg/kg i.v.). This finding rules out the possibility that flunarizine antagonism of cocaine effect might depend on DA autoreceptors blockade by flunarizine. It is suggested that flunarizine, by blocking calcium influx into DA neurons, prevents DA release from dendrites, thereby counteracting the main mechanism by which cocaine inhibits dopaminergic neuronal activity.

Caffeine-induced contractions in rabbit isolated renal artery are differentially inhibited by calcium antagonists

Caffeine (1–60 mM) induced concentration-dependent, endothelium-independent phasic contractile responses in isolated rabbit renal artery ring preparations. For concentrations of caffeine over 2 mM, responses were mainly the result of intracellular calcium ion mobilization since they were relatively resistant to removal of calcium ions from the bathing medium. The L-type slow calcium channel blocker, nifedipine (10 μM), had no effect and high concentrations of verapamil and diltiazem (10–30 μM) only slight and inconsistent effects (not concentration-dependent) upon these caffeine responses. Likewise, the highly lipophilic calcium antagonists flunarizine and lidoflazine (3–30 μM) only slightly displaced caffeine concentration-response curves to the right and reduced the maximum response. These small inhibitory effects of flunarizine and lidoflazine were not augmented in a calcium-free medium. In contrast, the other lipophilic calcium antagonists, bepridil and fendiline (3–30 μM), produced marked, non-competitive type inhibition of caffeine responses, completely inhibiting responses to the alkaloid at the highest concentration. Furthermore, the inhibitory effects of bepridil and fendiline were markedly augmented in calcium-free medium. These results clearly differentiate bepridil and fendiline from the other calcium antagonists studied. In addition they provide further evidence for effects other than at the cell membrane which could theoretically contribute to the efficacy of bepridil and fendiline as anti-anginal agents.