Blockade Of T-type Calcium Channels Research Articles

T-type calcium channel blockade induces apoptosis in C2C12 myotubes and skeletal muscle via endoplasmic reticulum stress activation.

Loss of T-type calcium channel (TCC) function has been reported to result in decreased cell viability and impaired muscle regeneration, but the underlying mechanisms remain largely unknown. We previously found that expression of TCC is reduced in aged pelvic floor muscle of multiple vaginal delivery mice, and this is related to endoplasmic reticulum stress (ERS) activation and autophagy flux blockade. In the present work, we further investigated the effects of TCC function loss on C2C12 myotubes and skeletal muscle, which is mediated by promotion of ERS and ultimately contributes to mitochondrial-related apoptotic cell death. We found that application of a TCC inhibitor induced mitochondria-related apoptosis in a dose-dependent manner and also reduced mitochondrial transmembrane potential (MMP), induced mito-ROS generation, and enhanced expression of mitochondrial apoptosis proteins. Functional inhibition of TCC induced ERS, resulting in disorder of Ca2+ homeostasis in endoplasmic reticulum, and ultimately leading to cell apoptosis in C2C12 myotubes. Tibialis anterior muscles of T-type α1H channel knockout mice displayed a smaller skeletal muscle fiber size and elevated ERS-mediated apoptosis signaling. Our data point to a novel mechanism whereby TCC blockade leads to ERS activation and terminal mitochondrial-related apoptotic events in C2C12 myotubes and skeletal muscles.

606 Small molecule blockade of T-type calcium channels by DX416 inhibits itch and reduces corresponding inflammation in acute and chronic itch mouse models

The processing of itch signals is regulated by many different ion channels. Among those are T-type calcium channels which are important regulators that contribute to the firing behavior of pruriceptors, or itch sensing neurons. The human genome encodes three different T-type channels: Cav3.1, Cav3.2, Cav3.3. It has been shown recently that pharmacological blockade of T-type calcium channels inhibits acute itch and that immune cells can express Cav 3 channels with roles in effector function. Thus, we hypothesized that local administration of the novel small molecule T-Type calcium channel inhibitor, DX416, would decrease cutaneous itch both through reducing pruriceptors signals triggering itch and decreasing local inflammatory immune responses potentiating itch.

Epigenetically Upregulated T-Type Calcium Channels Contribute to Abnormal Proliferation of Embryonic Neural Progenitor Cells Exposed to Valproic Acid.

Valproic acid is a clinically used mood stabilizer and antiepileptic drug. Valproic acid has been suggested as a teratogen associated with the manifestation of neurodevelopmental disorders, such as fetal valproate syndrome and autism spectrum disorders, when taken during specific time window of pregnancy. Previous studies proposed that prenatal exposure to valproic acid induces abnormal proliferation and differentiation of neural progenitor cells, presumably by inhibiting histone deacetylase and releasing the condensed chromatin structure. Here, we found valproic acid up-regulates the transcription of T-type calcium channels by inhibiting histone deacetylase in neural progenitor cells. The pharmacological blockade of T-type calcium channels prevented the increased proliferation of neural progenitor cells induced by valproic acid. Differentiated neural cells from neural progenitor cells treated with valproic acid displayed increased levels of calcium influx in response to potassium chloride-induced depolarization. These results suggest that prenatal exposure to valproic acid up-regulates T-type calcium channels, which may contribute to increased proliferation of neural progenitor cells by inducing an abnormal calcium response and underlie the pathogenesis of neurodevelopmental disorders.

717 Peripheral blockade of T-type calcium channels by DX416 inhibits acute itch and modulates immune response

717 Peripheral blockade of T-type calcium channels by DX416 inhibits acute itch and modulates immune response

Blockade of T-type calcium channels by 6-prenylnaringenin, a hop component, alleviates neuropathic and visceral pain in mice

Since Cav3.2 T-type Ca2+ channels (T-channels) expressed in the primary afferents and CNS contribute to intractable pain, we explored T-channel-blocking components in distinct herbal extracts using a whole-cell patch-clamp technique in HEK293 cells stably expressing Cav3.2 or Cav3.1, and purified and identified sophoraflavanone G (SG) as an active compound from SOPHORAE RADIX (SR). Interestingly, hop-derived SG analogues, (2S)-6-prenylnaringenin (6-PNG) and (2S)-8-PNG, but not naringenin, also blocked T-channels; IC50 (μM) of SG, (2S)-6-PNG and (2S)-8-PNG was 0.68–0.75 for Cav3.2 and 0.99–1.41 for Cav3.1. (2S)-6-PNG and (2S)-8-PNG, but not SG, exhibited reversible inhibition. The racemic (2R/S)-6-PNG as well as (2S)-6-PNG potently blocked Cav3.2, but exhibited minor effect on high-voltage-activated Ca2+ channels and voltage-gated Na+ channels in differentiated NG108-15 cells. In mice, the mechanical allodynia following intraplantar (i.pl.) administration of an H2S donor was abolished by oral or i.p. SR extract and by i.pl. SG, (2S)-6-PNG or (2S)-8-PNG, but not naringenin. Intraperitoneal (2R/S)-6-PNG strongly suppressed visceral pain and spinal ERK phosphorylation following intracolonic administration of an H2S donor in mice. (2R/S)-6-PNG, administered i.pl. or i.p., suppressed the neuropathic allodynia induced by partial sciatic nerve ligation or oxaliplatin, an anti-cancer agent, in mice. (2R/S)-6-PNG had little or no effect on open-field behavior, motor performance or cardiovascular function in mice, and on the contractility of isolated rat aorta. (2R/S)-6-PNG, but not SG, was detectable in the brain after their i.p. administration in mice. Our data suggest that 6-PNG, a hop component, blocks T-channels, and alleviates neuropathic and visceral pain with little side effects.

Selective Blockade of T-Type Ca2+ Channels is Protective Against Alcohol-Withdrawal Induced Seizure and Mortality.

We have previously demonstrated that blockade of T-type calcium channels by the non-selective antagonist, ethosuximide (ETX), is effective at reducing electrographical and behavioral correlates of alcohol-withdrawal (WD) seizure. Here, we investigated whether blockade of these calcium channels with the selective antagonist TTA-P2 also reduces alcohol-WD seizure. The non-specific T-type calcium channel antagonist, ETX, is protective against alcohol-WD seizure. However, the mechanism of this effect is unclear. Here, we provide evidence that further suggests selective blockade of T-type calcium channels are protective against alcohol-WD seizure and WD-related mortality. We used an intermittent ethanol exposure model to produce WD-induced hyperexcitability in DBA/2 J mice. Seizure severity was intensified with the chemoconvulsant pentylenetetrazole (PTZ). TTA-P2 (10 mg/kg) reduced seizure severity in mice undergoing alcohol WD with concurrent PTZ treatment (20 mg/kg). Moreover, TTA-P2 (20 and 40 mg/kg) was also protective against PTZ-induced (40 mg/kg) seizure and mortality. These results are consistent with prior results using ETX, and suggest that the protective effects of ETX and TTA-P2 against EtOH WD seizures are mediated by T-type calcium channels.

T-Type Calcium Channels Are Required to Maintain Viability of Neural Progenitor Cells.

T-type calcium channels are low voltage-activated calcium channels that evoke small and transient calcium currents. Recently, T-type calcium channels have been implicated in neurodevelopmental disorders such as autism spectrum disorder and neural tube defects. However, their function during embryonic development is largely unknown. Here, we investigated the function and expression of T-type calcium channels in embryonic neural progenitor cells (NPCs). First, we compared the expression of T-type calcium channel subtypes (CaV3.1, 3.2, and 3.3) in NPCs and differentiated neural cells (neurons and astrocytes). We detected all subtypes in neurons but not in astrocytes. In NPCs, CaV3.1 was the dominant subtype, whereas CaV3.2 was weakly expressed, and CaV3.3 was not detected. Next, we determined CaV3.1 expression levels in the cortex during early brain development. Expression levels of CaV3.1 in the embryonic period were transiently decreased during the perinatal period and increased at postnatal day 11. We then pharmacologically blocked T-type calcium channels to determine the effects in neuronal cells. The blockade of T-type calcium channels reduced cell viability, and induced apoptotic cell death in NPCs but not in differentiated astrocytes. Furthermore, blocking T-type calcium channels rapidly reduced AKT-phosphorylation (Ser473) and GSK3β-phosphorylation (Ser9). Our results suggest that T-type calcium channels play essential roles in maintaining NPC viability, and T-type calcium channel blockers are toxic to embryonic neural cells, and may potentially be responsible for neurodevelopmental disorders.

Anatomical localization of Cav3.1 calcium channels and electrophysiological effects of T-type calcium channel blockade in the motor thalamus of MPTP-treated monkeys.

Conventional anti-Parkinsonian dopamine replacement therapy is often complicated by side effects that limit the use of these medications. There is a continuing need to develop nondopaminergic approaches to treat Parkinsonism. One such approach is to use medications that normalize dopamine depletion-related firing abnormalities in the basal ganglia-thalamocortical circuitry. In this study, we assessed the potential of a specific T-type calcium channel blocker (ML218) to eliminate pathologic burst patterns of firing in the basal ganglia-receiving territory of the motor thalamus in Parkinsonian monkeys. We also carried out an anatomical study, demonstrating that the immunoreactivity for T-type calcium channels is strongly expressed in the motor thalamus in normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. At the electron microscopic level, dendrites accounted for >90% of all tissue elements that were immunoreactive for voltage-gated calcium channel, type 3.2-containing T-type calcium channels in normal and Parkinsonian monkeys. Subsequent in vivo electrophysiologic studies in awake MPTP-treated Parkinsonian monkeys demonstrated that intrathalamic microinjections of ML218 (0.5 μl of a 2.5-mM solution, injected at 0.1-0.2 μl/min) partially normalized the thalamic activity by reducing the proportion of rebound bursts and increasing the proportion of spikes in non-rebound bursts. The drug also attenuated oscillatory activity in the 3-13-Hz frequency range and increased gamma frequency oscillations. However, ML218 did not normalize Parkinsonism-related changes in firing rates and oscillatory activity in the beta frequency range. Whereas the described changes are promising, a more complete assessment of the cellular and behavioral effects of ML218 (or similar drugs) is needed for a full appraisal of their anti-Parkinsonian potential.

Enhanced BDNF signalling following chronic hypoxia potentiates catecholamine release from cultured rat adrenal chromaffin cells

We investigated the role of the neurotrophin BDNF signalling via the TrkB receptor in rat adrenomedullary chromaffin cells (AMCs) exposed to normoxia (Nox; 21% O2) and chronic hypoxia (CHox; 2% O2) in vitro for ∼ 48 h. TrkB receptor expression was upregulated in primary AMCs and in immortalized chromaffin (MAH) cells exposed to CHox; this effect was absent in MAH cells deficient in the transcription factor, hypoxia inducible factor (HIF)-2α. Relative to normoxic controls, activation of the TrkB receptor in chronically hypoxic AMCs led to a marked increase in membrane excitability, intracellular [Ca(2+)], and catecholamine secretion. The BDNF-induced rise of intracellular [Ca(2+)] in CHox cells was sensitive to the selective T-type Ca(2+) channel blocker TTA-P2 and tetrodotoxin (TTX), suggesting key roles of low threshold T-type Ca(2+) and voltage-gated Na(+) channels in the signalling pathway. Environmental stressors, including chronic hypoxia, enhance the ability of adrenomedullary chromaffin cells (AMCs) to secrete catecholamines; however, the underlying molecular mechanisms remain unclear. Here, we investigated the role of brain-derived neurotrophic factor (BDNF) signalling in rat AMCs exposed to chronic hypoxia. In rat adrenal glands, BDNF and its tropomyosin-related kinase B (TrkB) receptor are highly expressed in the cortex and medulla, respectively. Exposure of AMCs to chronic hypoxia (2% O2; 48 h) in vitro caused a significant increase to TrkB mRNA expression. A similar increase was observed in an immortalized chromaffin cell line (MAH cells); however, it was absent in MAH cells deficient in the transcription factor HIF-2α. A specific TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF), stimulated quantal catecholamine secretion from chronically hypoxic (CHox; 2% O2) AMCs to a greater extent than normoxic (Nox; 21% O2) controls. Activation of TrkB by BDNF or 7,8-DHF increased intracellular Ca(2+) ([Ca(2+)]i), an effect that was significantly larger in CHox cells. The 7,8-DHF-induced [Ca(2+)]i rise was sensitive to the tyrosine kinase inhibitor K252a and nickel (2 mm), but not the Ca(2+) store-depleting agent cyclopiazonic acid. Blockade of T-type calcium channels with TTA-P2 (1 μm) or voltage-gated Na(+) channels with TTX inhibited BDNF-induced [Ca(2+)]i increases. BDNF also induced a dose-dependent enhancement of action potential firing in CHox cells. These data demonstrate that during chronic hypoxia, enhancement of BDNF-TrkB signalling increases voltage-dependent Ca(2+) influx and catecholamine secretion in chromaffin cells, and that T-type Ca(2+) channels play a key role in the signalling pathway.

Z944: a first in class T-type calcium channel modulator for the treatment of pain.

Zalicus, Inc. is a small, publicly-traded biotech company in Cambridge, Massachusetts. The potential target for neuropathic pain lies in the T-type calcium channels, members of the low-voltage activated channel family. By opening at relatively negative membrane depolarizations, T-type channels can act as modulators of the threshold of the action potential by increasing the calcium current, leading to further depolarization of the cell and activation of other calcium channels, and ultimately, sodium and potassium channels. This is a target that is widely expressed in both the peripheral as well as the central nervous system (Zamponi et al., 2009). It is known that T-type calcium channel blockade can modulate pain behavior and disrupting this mechanism can reduce pain in neuropathic, inflammatory, and visceral pain models. There is evidence that the calcium channel protein itself as well as the current that is delivered by this channel is increased in certain pain models (Marger et al., 2011). Another important feature of this target is its central action. There are three subtypes of the T-type calcium channel, denoted Cav3.1, 3.2, and 3.3. They are expressed in different places in the thalamus, the cerebellum, and other parts of the brain. It is thought that they participate in the regulation of connectivity or crosstalk between the sensory nervous system and the cortex by promoting thalamic neuron burst firing and network oscillations important for relay and interpretation of signals to and by the cortex. A number of central nervous system (CNS) diseases have been linked to aberrant thalamocortical oscillations (thalamocortical dysrhythmia), and there is evidence that T-type calcium channel mutants can play a role in hyperexcitability disorders, for example, epilepsy syndromes. Some approved anticonvulsants also hit the T-type channel as part of their polypharmacology. Zalicus' approach has been to discover and develop a small molecule blocker of T-type calcium channels as a potential therapeutic for pain. The medication, Z944, is a novel, oral, state-dependent, selective T-type calcium channel blocker. This blocker has >150-fold selectivity vs. non-T-type voltage-gated ion channels and has been shown to inhibit native neuronal T-type currents at high potency. The blockade of Cav3.2 by Z944 is more pronounced during high-frequency firing and may provide some advantage to the molecule by selectively targeting a pathological state of the channel (Short et al., 2013). A phase 1, double-blind, placebo-controlled study to determine the safety, tolerability, and pharmacokinetics of single and multiple ascending doses of oral Z944 in healthy male subjects in the fed and fasted states using an immediate release formulation showed that the medication was safe and well tolerated. Mild and expected CNS side effects were observed; no serious adverse events were reported. A phase 1b clinical study utilized a state-of-the-art experimental clinical model measuring Laser-Evoked Potentials (LEP) from skin irritated following topical application of capsaicin (modeling neuropathic pain signaling and central sensitization) or exposure to UV light (modeling inflammatory pain signaling). Healthy volunteers received 20, 40, and 80 mg doses split in four administrations every 2 h vs. placebo. The data showed that Z944 reduced peak-to-peak amplitudes of LEPs from both capsaicin and UV irritated skin models and reduced subjective Visual Analog Scale (VAS) pain scores in both skin types. The noted adverse events were generally mild to moderate and primarily central nervous system related. No serious adverse events occurred in this study. On the basis of these findings, several modified release formulations of Z944 are currently being advanced in clinical development for pain indications.

Inhibition of cellular proliferation and induction of apoptosis in human lung adenocarcinoma A549 cells by T-type calcium channel antagonist

The anti-proliferative and apoptotic activities of new T-type calcium channel antagonist, 6e (BK10040) on human lung adenocarcinoma A549 cells were investigated. The MTT assay results indicated that BK10040 was cytotoxic against human lung adenocarcinoma (A549) and pancreatic cancer (MiaPaCa2) cells in a dose-dependent manner with IC50 of 2.25 and 0.93μM, respectively, which is ca. 2-fold more potent than lead compound KYS05090 despite of its decreased T-type calcium channel blockade. As a mode of action for cytotoxic effect of BK10040 on lung cancer (A549) cells, this cancer cell death was found to have the typical features of apoptosis, as evidenced by the accumulation of positive cells for annexin V. In addition, BK10040 triggered the activations of caspases 3 and 9, and the cleavages of poly (ADP-ribose) polymerase (PARP). Moreover, the treatment with z-VAD-fmk (a broad spectrum caspase inhibitor) significantly prevented BK10040-induced apoptosis. Based on these results, BK10040 may be used as a potential therapeutic agent for human lung cancer via the potent apoptotic activity.

Role of specific T-type calcium channel blocker R(−) efonidipine in the regulation of renal medullary circulation

Blockade of the T-type calcium channel (TCC), which is expressed in the renal efferent arterioles of the juxtamedullary nephron and vasa recta, has been shown to protect against renal injury. Studies were designed to determine the effects of a specific TCC blocker, R(-) efonidipine [R(-)EFO], on the regulation of renal circulation. Renal medullary blood flux (MBF) and cortical blood flux (CBF) were simultaneously monitored using laser-Doppler flowmetry in Sprague-Dawley rats. Responses were also determined in rats with angiotensin II (AngII) induced renal ischemia. Intravenous (i.v.) or renal interstitial (r.i.) infusion of R(-)EFO (0.25 mg/h, i.v. or r.i.) significantly increased MBF by 24.0 ± 7.0 and 21.0 ± 4.4%, respectively, but without changing CBF or mean arterial pressure. The nitric oxide (NO) synthase inhibitor NG-nitro-L-argininemethylester (L-NAME, 1 μg/kg per min, i.v. or r.i.) significantly attenuated R(-)EFO-induced increase in MBF. R(-)EFO inhibited the AngII-mediated (50 ng/kg per min, i.v.) reduction of MBF (28.4 ± 1.7%), which was associated with increased urinary NO(2) + NO(3) excretion and decreased urinary hydrogen peroxide (H(2)O(2)) excretion. Intracellular H(2)O(2) fluorescence (real-time fluorescence imaging) in the epithelial cells of isolated medullary thick ascending limb (mTAL) significantly increased following AngII stimulation (1 μmol/L, 235 ± 52 units), which was significantly inhibited by pre and coincubation with R(-)EFO. R(-)EFO stimulation also increased the intracellular NO concentration in the epithelial cells of mTAL (220 ± 62 units). These results suggest that TCC blockade with R(-)EFO selectively increases MBF, an effect that appears to be mediated by changes in renal NO and oxidative stress balance, which may protect against ischemic renal injury in the renal medullary region.

Effect of Benidipine Hydrochloride, a Long-acting T-type Calcium Channel Blocker, on Blood Pressure and Renal Function in Hypertensive Patients with Diabetes mellitus

Calcium channel blockers are commonly used to treat hypertension, and are known to generally act on the L-type calcium channel. Recent studies have shown, however, that some calcium channel blockers also block other calcium channel subtypes, including N- and T-type channels. Cilnidipine (CAS 132203-70-4) is an L- and N-type calcium channel blocker, and benidipine hydrochloride (benidipine, CAS 91599-74-5) is known to inhibit the T-type as well as L- and N-type calcium channels. In this study, effects of switching from cilnidipine to benidipine on blood pressure (BP) lowering and renal functions were investigated in order to clarify the physiological properties of the T-type calcium channel. Forty hypertensive patients with diabetes and poor BP control despite receiving cilnidipine were selected, and the changes in BP and urine protein (UP) scores were investigated retrospectively after switching from cilnidipine to benidipine for more than 3 months. BP (systolic/diastolic) significantly decreased from 155.8 +/- 13.7 mmHg/76.5 +/- 13.3 mmHg to 145.9 +/- 17.0 mmHg/71.4 +/- 13.7 mmHg after benidipine treatment, and this effect was stably maintained for one year. UP also significantly decreased from 1.29 to 0.67 in the mean score. The decrease in UP may be explained by a mechanism other than BP lowering effect. These results demonstrate that benidipine has a more potent antihypertensive effect than cilnidipine and also a renoprotective effect, indicating the high usefulness of benidipine in hypertensive patients with diabetes. T-type calcium channel blockade was suggested to be possibly involved in the enoprotective effect of benidipine.

Benidipine, a dihydropyridine L-type/T-type calcium channel blocker, affords additive benefits for prevention of cardiorenal injury in hypertensive rats

Benidipine is a dihydropyridine calcium channel blocker inhibiting not only L-type but also T-type calcium channels. To elucidate potential additive benefit of benidipine for prevention of cardiorenal injury, we compared the cardiac and renal protective effects of equihypotensive doses of benidipine and cilnidipine in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP were divided into five groups, and were given vehicle, benidipine at 1 or 3 mg/kg per day, or cilnidipine at 1 or 3 mg/kg per day for 7 weeks, and the protective effects against cardiorenal injury were compared among each group. Benidipine and cilnidipine at the same doses exerted comparable hypotensive effects on SHRSP throughout the treatment. Despite equihypotensive effects between both drugs, benidipine prevented cardiac hypertrophy, fibrosis, and inflammation to a greater extent than cilnidipine. Moreover, benidipine prevented glomerulosclerosis, tubulointerstitial injury, and renal inflammation more than cilnidipine. To elucidate the underlying mechanism of more beneficial effects of benidipine than cilnidipine, we compared the effects of these drugs on cardiac and renal oxidative stress, and aldosterone in SHRSP. Benidipine reduced both cardiac and renal NADPH oxidase activities in SHRSP more than cilnidipine, being associated with more attenuation of cardiac and renal superoxide by benidipine. Furthermore, serum aldosterone was significantly reduced by benidipine but not by cilnidipine. Benidipine exerted more protective effects against cardiorenal injury of hypertensive rats than cilnidipine, through more attenuation of oxidative stress than cilnidipine, and the reduction of aldosterone. Benidipine, via blockade of T-type calcium channels, seems to elicit additive benefits for prevention of hypertensive cardiorenal injury.

T-type calcium channel blockade as a therapeutic strategy against renal injury in rats with subtotal nephrectomy

T-type calcium channel blockers have been previously shown to protect glomeruli from hypertension by regulating renal arteriolar tone. To examine whether blockade of these channels has a role in protection against tubulointerstitial damage, we used a stereo-selective T-type calcium channel blocker R(-)-efonidipine and studied its effect on the progression of this type of renal injury in spontaneously hypertensive rats that had undergone subtotal nephrectomy. Treatment with racemic efonidipine for 7 weeks significantly reduced systolic blood pressure and proteinuria. The R(-)-enantiomer, however, had no effect on blood pressure but significantly reduced proteinuria compared to vehicle-treated rats. Both agents blunted the increase in tubulointerstitial fibrosis, renal expression of alpha-smooth muscle actin and vimentin along with transforming growth factor-beta (TGF-beta)-induced renal Rho-kinase activity seen in the control group. Subtotal nephrectomy enhanced renal T-type calcium channel alpha1G subunit expression mimicked in angiotensin II-stimulated mesangial cells or TGF-beta-stimulated proximal tubular cells. Our study shows that T-type calcium channel blockade has renal protective actions that depend not only on hemodynamic effects but also pertain to Rho-kinase activity, tubulointerstitial fibrosis, and epithelial-mesenchymal transitions.

Randomized comparison of T-type versus L-type calcium-channel blockade on exercise duration in stable angina: Results of the Posicor Reduction of Ischemia During Exercise (PRIDE) trial

Background Mibefradil is a T-type calcium-channel antagonist and arterial vasodilator with negative chronotropic effects. It is not known if T-type calcium-channel blockade is superior to L-type calcium-channel blockade in patients with stable angina pectoris. Methods A multicenter, randomized, double-blind trial was conducted in patients with documented coronary disease and stable angina to compare a 360 mg dose of diltiazem CD with 100 mg dose of mibefradil. The primary end point was change in time to symptom-limited exercise termination from baseline to 8 weeks. Secondary efficacy parameters included time to onset of persistent ST-segment depression, time to awareness of angina, and change in exercise duration from baseline to 2 and 4 weeks of treatment. Results A total of 121 patients were randomized to mibefradil and 113 to diltiazem CD. At 8 weeks, the increase in exercise duration was 24.5 seconds greater in the mibefradil group (P =.017; 95% CI 4.4-44.7 seconds). At 8 weeks, time to development of ≥1 mm ST-segment depression was greater by 45.3 seconds (P =.0025; 95% CI 16.2-74.5) with mibefradil, but time to development of angina was not significantly different. Conclusion T-type calcium-channel antagonism with mibefradil improved treadmill exercise parameters compared with diltiazem in patients with chronic stable angina. Further investigation and development of antagonists of T-type calcium channels with fewer adverse drug interactions is warranted and may be promising in the management of ischemic heart disease. (Am Heart J 2002;144:60-7.)

L-type and T-type calcium channel blockade potentiate the analgesic effects of morphine and selective μ opioid agonist, but not to selective δ and κ agonist at the level of the spinal cord in mice

We examined the effects of amlodipine, a selective L-type voltage dependent Ca 2+ channel (VDCC) blocker, and mibefradil, a selective T-type VDCC blocker on the antinociceptive effects of morphine, and μ, δ and κ opioid receptor selective agonist-induced antinociception at the spinal level. Intrathecally administered amlodipine and mibefradil potentiated morphine and [ d-Ala 2, N mePhe 4, Gly-ol 5] enkephalin (DAMGO)-induced antinociception by shifting their dose response curves to the left. However, intrathecally administered amlodipine and mibefradil did not affect [ d-Pen 2, D-Pen 5]enkephalin (DPDPE) and [trans-(±)-3,4-dichloro- N-methyl- N-[2-(1-pyrolidinyl)cyclohexyl] benzene acetamide (U-50, 488H)-induced antinociception. These data indicate that L-type and T-type VDCC blockers synergistically potentiate the analgesic effects of μ opioid receptor agonists, but not δ and κ opioid receptor agonists, at the spinal level. Additionally, these data suggest that there is an important functional interaction between L-type and/ or T-type VDCC and μ opioid receptors in the process of analgesia.

Comparative effects of mibefradil and nifedipine gastrointestinal transport system on autonomic function in patients with mild to moderate essential hypertension

L-type dihydropyridine calcium channel blockers (CCBs) have been implicated in increased cardiovascular events in patients with hypertension, perhaps due to adverse effects on autonomic nervous system (ANS) function. Blockade of T-type calcium channels may limit ANS dysfunction by inhibition of T channel-mediated neuroendocrine effects. This double-blind, parallel group study compared the effect of nifedipine gastrointestinal transport system (GITS) (L-type CCB) versus mibefradil (T-type CCB) on ANS function in patients with mild-moderate essential hypertension. Sixteen patients (10 male, 6 female; age 57.2 +/- 2.3 years), diastolic blood pressure (DBP) < 95 mmHg were randomized to nifedipine 30 mg daily or mibefradil 50 mg daily (2 weeks), then nifedipine 60 mg daily or mibefradil 100 mg daily (4 weeks). Sympathetic nervous system activity (SNSA) was assessed using norepinephrine kinetics. Parasympathetic nervous system activity (PSNA) was assessed from 24 h Holter recordings of heart rate variability (HRV). Non-invasive baroreflex sensitivity (BRS) provided integrated assessment of ANS. Patient groups were well matched at baseline. Achieved DBP was lower in patients treated with mibefradil compared with nifedipine, (83.4 +/- 1.7 versus 95.25 +/- 3.3 mmHg). There were no significant differences in SNSA and BRS between groups, however the root mean square of successive differences and high frequency power (HFP) were increased in mibefradil compared with nifedipine-treated patients [(+ 1.07 +/- 1.6 versus -3.36 +/- 1.2 ms, P < 0.05) and (+ 0.28 +/- 0.1 versus -0.23 +/- 0.1 ms2, P < 0.01), respectively]. Furthermore, Ln HFP/Ln total power was increased from week 0 to week 6 in the mibefradil-treated group, (0.71 +/- 0.02 versus 0.74 +/- 0.03, P = 0.046). No differences existed between effect of L- and T-type CCBs on SNSA and BRS. However, T-type CCBs increased PSNA, independent of achieved changes in heart rate.

T-type calcium channel blockade blocks bromocriptine-induced locomotor stimulation in mice

T-type calcium channel blockade blocks bromocriptine-induced locomotor stimulation in mice

Mibefradil, a T-Type Channel-Selective Calcium Antagonist: Clinical Trials in Chronic Stable Angina Pectoris

Pharmacotherapy with nitrates, β-blockers, and calcium antagonists is the cornerstone of management of patients with chronic stable angina pectoris. While these agents are all effective, their use may be limited by pharmacologic tolerance, side effects, and drug interactions. Mibefradil is a recently developed calcium antagonist with a unique chemical structure, pharmacologic profile, and mode of action. Unlike all previously available calcium antagonists, mibefradil acts primarily by selective blockade of T-type calcium channels, rather than L-type channels, at clinically relevant concentrations. It has been evaluated as a treatment for angina in placebo-controlled and active-controlled clinical trials. Treatment with 50 mg mibefradil resulted in a significant improvement in exercise tolerance test duration in three of the five placebo-controlled trials, and a significant improvement in time to onset of angina in two of the five trials. Time to onset of ischemia as evaluated by 0.1 mV ST-segment depression was increased in all five placebo-controlled trials. Treatment with 100 mg mibefradil resulted in significant improvement in all three exercise tolerance test parameters in all studies. Mibefradil further improved exercise tolerance test duration and other efficacy parameters when administered concomitantly to patients on background β-blocker or nitrate therapy. In addition, treatment with mibefradil was associated with a dose-dependent decrease in heart rate, double product, frequency of anginal attacks, nitroglycerin consumption, and both frequency and duration of silent ischemic episodes. In comparative trials, 100 mg mibefradil once daily was superior in efficacy to 10 mg amlodipine once daily and was at least equivalent to diltiazem in both efficacy and tolerability. Mibefradil was safe and well tolerated in all studies.