Blockade Of N-type Calcium Channels Research Articles

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

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

ID:15841 A Case of Prolonged Psychosis With Intrathecal Ziconotide

Chronic refractory pain can be difficult to manage. Intrathecal Ziconotide has proven to be effective at treating refractory nociceptive and neuropathic pain. Ziconotide’s analgesic effect is via selective blockade of N-type calcium channels. Ziconotide is trialed with a bolus of 3 mcg or 5 mcg. After intrathecal pump implant, therapy is initiated at 1.2-2.4 mcg/day. After 7-14 days the medication is exchanged and the dose kept the same. Subsequently, the dose is titrated every 7-14 days by 0.5-1.2 mcg/day.

Dopamine and Serotonin-Induced Modulation of GABAergic and Glutamatergic Transmission in the Striatum and Basal Forebrain.

Catecholamine receptor-mediated modulation of glutamatergic or GABAergic transmission in the striatum as well as basal forebrain (BF) has been intensively studied during these two decades. In the striatum, activation of dopamine (DA) D2 receptors in GABAergic terminals inhibits GABA release onto cholinergic interneurons by selective blockade of N-type calcium channels. In the BF, glutamatergic transmission onto cholinergic projection neurons is inhibited via DA D1-like receptors by selective blockade of P/Q-type calcium channels. On the other hand, presynaptic inhibition of the GABA release onto cholinergic neurons mediated by D1-like receptors or 5-HT1B receptors is independent of calcium influx. In addition, the DA receptor-mediated calcium influx dependent presynaptic inhibition mentioned above decreases with postnatal development, with selective coupling between DA receptors and each subtype of calcium channels being unchanged. Furthermore, the precise origin of these GABAergic or glutamatergic inputs to postsynaptic neurons can be identified by recent optogenetic approaches. Thus, modulatory mechanisms in specific synaptic connections between certain types of neurons in the striatum and BF are being identified.

Comparison of the effects of L-type calcium channel antagonist Amlodipine with L/N-type calcium channel antagonist Cilnidipine on blood pressure, heart rate, proteinuria and lipid profile in hypertensive patients

Background: Cilnidipine is a novel and unique 1,4-dydropyridine derivative calcium antagonist that exerts potent inhibitory actions not only on L-type but also on N-type voltage dependent calcium channels. Blockade of the neural N-type calcium channel inhibits the secretion of norepinephrine from peripheral neural terminals and depresses sympathetic nervous system activity.Objective and methods: The purpose of this study was to assess the effect of Cilnidipine and Amlodipine on blood pressure (BP) levels. We did BP monitoring before and after once-daily use of Cilnidipine and Amlodipine in 100 hypertensive patients.Results: Both drugs significantly reduced systolic BP (SBP) and diastolic BP (DBP). However, the reductions in pulse rate (PR) were significantly greater in the Cilnidipine group than the Amlodipine group. N-type calcium channel blockade by Cilnidipine may not cause reflex tachycardia, and may be useful for hypertensive treatment.Conclusion: There was significant reduction in proteinuria with Clindipine as compared to Amlodipine. However, there were no significant change in total cholesterol level in diabetes and non-diabetics in both the group.Bangladesh Journal of Medical Science Vol.15(3) 2016 p.460-465

Discovery of a 1-isopropyltetrahydroisoquinoline derivative as an orally active N-type calcium channel blocker for neuropathic pain

N-type calcium channel blockade is a promising therapeutic approach for the treatment of neuropathic pain. Starting from lead compound (S)-1, we focused our optimization efforts on potency for N-type calcium channel inhibition and improvement of CYP inhibition profile. 2-{[(1-Hydroxycyclohexyl)methyl]amino}-(1R)-(1-isopropyl-6-methoxy-3,4-dihydroisoquinolin-2(1H)-yl)ethanone oxalate ((R)-5r) was identified as a novel orally active small-molecule N-type calcium channel inhibitor with reduced CYP inhibition liability. Oral administration of (R)-5r improved mechanical allodynia in a spinal nerve ligation model of neuropathic pain in rats with an ED50 value of 2.5mg/kg.

Gq-DREADD Selectively Initiates Glial Glutamate Release and Inhibits Cue-induced Cocaine Seeking

BackgroundGlial cells of the central nervous system directly influence neuronal activity by releasing neuroactive small molecules, including glutamate. Long-lasting cocaine-induced reductions in extracellular glutamate in the nucleus accumbens core (NAcore) affect synaptic plasticity responsible for relapse vulnerability. MethodsWe transduced NAcore astrocytes with an adeno-associated virus vector expressing hM3D designer receptor exclusively activated by a designer drug (DREADD) under control of the glial fibrillary acidic protein promoter in 62 male Sprague Dawley rats, 4 dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor mice, and 4 wild-type littermates. Using glutamate biosensors, we measured NAcore glutamate levels following intracranial or systemic administration of clozapine N-oxide (CNO) and tested the ability of systemic CNO to inhibit reinstated cocaine or sucrose seeking following self-administration and extinction training. ResultsAdministration of CNO in glial fibrillary acidic protein-hM3D-DREADD transfected animals increased NAcore extracellular glutamate levels in vivo. The glial origin of released glutamate was validated by an absence of CNO-mediated release in mice expressing a dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor variant in glia. Also, CNO-mediated release was relatively insensitive to N-type calcium channel blockade. Systemic administration of CNO inhibited cue-induced reinstatement of cocaine seeking in rats extinguished from cocaine but not sucrose self-administration. The capacity to inhibit reinstated cocaine seeking was prevented by systemic administration of the group II metabotropic glutamate receptor antagonist LY341495. ConclusionsDREADD-mediated glutamate gliotransmission inhibited cue-induced reinstatement of cocaine seeking by stimulating release-regulating group II metabotropic glutamate receptor autoreceptors to inhibit cue-induced synaptic glutamate spillover.

L-/N-type Calcium Channel Blockers and Proteinuria

The first-line depressor agents for hypertensive patients with chronic kidney disease are the renin-angiotensin system inhibitors because of their antiproteinuric and reno-protective effects. However, only one renin-angiotensin system inhibitor often cannot achieve target blood pressure in patients with injured kidney. Thus, second-line antihypertensives are required. Calcium channel blockers are frequently added on the renin-angiotensin system inhibitors in hypertensive patients with chronic kidney disease. However, they do not always show reno-protective effects because of their glomerular pressure-increasing action; Antihypetensive calcium channel blockers suppress L-type calcium channels, which exist in glomerular afferent but not efferent arterioles, and their afferent arteriole-specific vasodilation causes glomerular hypertension. The decrease in glomerular pressure due to their systemic hypotesive effect is counteracted by the glomerular pressure-incresing action. However, L-/N-type calcium channel blockers inhibits norepinephrine release from the sympathetic nerve terminal by blockade of N-type calcium channels, and dilate both afferent and efferent arterioles, which were innervated sympathetically, resulting in decrease in glomerular pressure. Actually, we have demonstrated that an L-/N-type calcium channel blocker cilnidipine decreased urinary protein more greatly than an L-type calcium channel blocker amlodipine in the renin-angiotensin system inhibitor-treated patients with chronic kidney disease. Thus, L-/N-type calcium channel blockers are one of suitable candidates for the second-line antihypertensives in the renin-angiotensin system inhibitor-treated hypertensive patients with proteinuria.

Additive effects of cilnidipine and angiotensin II receptor blocker in preventing the progression of diabetic nephropathy in diabetic spontaneously hypertensive rats

Cilnidipine (Cil) is an L/N-type calcium channel blocker (CCB) that is known to provide renal protection by decreasing the activity of the sympathetic nervous system and the renin-angiotensin system (RAS). However, very few studies have evaluated the renoprotective effects of Cil in hypertension complicated by diabetes mellitus. In this study, we compared the effects of cilnidipine and the L-type CCB, amlodipine (Aml), in combination with an angiotensin II receptor blocker (ARB) on diabetic nephropathy that developed as a result of inducing diabetes in hypertensive rats. Diabetes was induced in 9-week-old male spontaneously hypertensive rats by intraperitoneally injecting them with streptozotocin (40 mg/kg twice) and the rats (8 per group) were randomly assigned to receive valsartan (Val), Cil + Val, Aml + Val, or vehicle for 8 weeks through a gastric tube. There were no significant differences in systolic blood pressure or plasma parameters between the two combination therapy groups. Blood pressure lowering by neither combination therapy significantly affected the glycemic variables. However, the increased glycogen levels in the kidney as a result of hyperglycemia were significantly suppressed in the groups that received combination therapy, and the increased proteinurea and glomerulosclerosis due to progression of the diabetic nephropathy were significantly suppressed in the Cil + Val group. In addition, a significant decrease in ED-1-positive cells was observed in the Cil + Val group alone. The results of this study suggested that the L/N-type CCB, cilnidipine, had additive antihypertensive and proteinuria-lowering effects when administered in combination with an ARB, even in type-1 diabetic rats, and that the L-type CCB, amlodipine, did not. Furthermore, combination therapy with cilnidipine and valsartan significantly reduced glycogen accumulation and ED-1-positive cell infiltration, suggesting that cilnidipine suppressed the excessive increase in the activity of the sympathetic nervous system and RAS through N-type calcium channel blockade.

Renoprotective and antioxidant effects of cilnidipine in hypertensive patients

Cilnidipine, an L/N-type calcium channel blocker (CCB), has been reported to have more beneficial effects on proteinuria progression in hypertensive patients than amlodipine, an L-type CCB. The N-type calcium channel blockade that inhibits renal sympathetic nerve activity might reduce glomerular hypertension by facilitating vasodilation of the efferent arterioles. However, the precise mechanism of the renoprotective effect of cilnidipine remains unknown. Because cilnidipine exerted significantly higher antioxidant activity than amlodipine in cultured human mesangial cells, we hypothesized that cilnidipine might exert a renoprotective effect by suppressing oxidative stress. A total of 35 hypertensive patients receiving a renin-angiotensin system inhibitor were randomly assigned to a cilnidipine (n=18; 10 mg per day cilnidipine titrated to 20 mg per day) or amlodipine (n=17; 5 mg per day amlodipine titrated to 10 mg per day) group; the target blood pressure (BP) was set at 130/85 mmHg. After 6 months of treatment, systolic and diastolic BPs were significantly reduced in both of the groups, without any significant difference between the groups. The urinary albumin, 8-hydroxy-2'-deoxyguanosine (OHdG) and liver-type fatty-acid-binding protein (L-FABP) to creatinine ratios significantly decreased in the cilnidipine group (P<0.05) compared with those in the amlodipine group. The reductions in urinary albumin, 8-OHdG and L-FABP were not correlated with the change in systolic BP. In conclusion, cilnidipine, but not amlodipine, ameliorated urinary albumin excretion and decreased urinary 8-OHdG and L-FABP in the hypertensive patients. Cilnidipine probably exerts a greater renoprotective effect through its antioxidative properties.

Structure–activity relationships of trimethoxybenzyl piperazine N-type calcium channel inhibitors

We previously reported the small organic N-type calcium channel blocker NP078585 that while efficacious in animal models for pain, exhibited modest L-type calcium channel selectivity and substantial off-target inhibition against the hERG potassium channel. Structure–activity studies to optimize NP078585 preclinical properties resulted in compound 16, which maintained high potency for N-type calcium channel blockade, and possessed excellent selectivity over the hERG (∼120-fold) and L-type (∼3600-fold) channels. Compound 16 shows significant anti-hyperalgesic activity in the spinal nerve ligation model of neuropathic pain and is also efficacious in the rat formalin model of inflammatory pain.

Effects of an N-Type Calcium Antagonist on Angiotensin II-Renin Feedback

Background: Interrupting the renin-angiotensin system (RAS) with an angiotensin II receptor blocker (ARB) has been found to induce RAS overactivation. In this study, we investigated the effect of 2 calcium channel blockers (CCBs), cilnidipine (L-/N-type CCB) and amlodipine (L-type CCB), on the RAS activation induced by an ARB in a strain of spontaneously hypertensive rats (SHR/Izm, 10 weeks of age). Methods: Rats intravenously catheterized for blood collection were randomly divided into groups that were administered the vehicle, the ARB valsartan or valsartan combined with one of the 2 CCBs. Their blood and kidneys were collected 270 min after administration. Results: Valsartan increased the plasma angiotensin II (Ang II) level in a dose-dependent manner. Cilnidipine suppressed the increase in plasma renin activity and plasma Ang II levels induced by valsartan, but amlodipine did not. Combined administration of cilnidipine, but not amlodipine, and valsartan significantly reduced the noradrenaline content in the renal cortex. Conclusions: The results of this study suggest that the suppressive effect of cilnidipine on the valsartan-induced increase in RAS activity can be partly explained by its sympatholytic action mediated by N-type calcium channel blockade, and that combined administration of cilnidipine and valsartan might provide a synergistic therapeutic effect.

Chronic intermittent hypoxia affects integration of sensory input by neurons in the nucleus tractus solitarii

The autonomic nervous and respiratory systems, as well as their coupling, adapt over a wide range of conditions. Chronic intermittent hypoxia (CIH) is a model for recurrent apneas and induces alterations in breathing and increases in sympathetic nerve activity which may ultimately result in hypertension if left untreated. These alterations are believed to be due to increases in the carotid body chemoreflex pathway. Here we present evidence that the nucleus tractus solitarii (nTS), the central brainstem termination site of chemoreceptor afferents, expresses a form of synaptic plasticity that increases overall nTS activity following intermittent hypoxia. Following CIH, an increase in presynaptic spontaneous neurotransmitter release occurs under baseline conditions. Furthermore, during and following afferent stimulation there is an augmentation of spontaneous transmitter release that occurs out of synchrony with sensory stimulation. On the other hand, afferent evoked synchronous transmitter release is attenuated. Overall, this shift from synchronous to asynchronous transmitter release enhances nTS cellular discharge. The role of the neurotransmitter dopamine in CIH-induced plasticity is also discussed. Dopamine attenuates synaptic transmission in nTS cells by blockade of N-type calcium channels, and this mechanism occurs tonically following normoxia and CIH. This dopaminergic pathway, however, is not altered in CIH. Taken together, alterations in nTS synaptic activity may play a role in the changes of chemoreflex function and cardiorespiratory activity in the CIH apnea model.

Spinal mechanism of standard analgesics: Evaluation using mouse models of allodynia

Spinal neurotransmission plays an important role in the perception of pain signaling. In the present study, we investigated the spinal anti-nociceptive mechanism of current standard analgesics in mouse models of tactile allodynia induced by intrathecal administration of N-methyl-D-aspartic acid (NMDA), prostaglandin E2 (PGE2), and bicuculline. NMDA-induced allodynia is induced by postsynaptic NMDA receptor activation, while PGE2-induced allodynia is triggered by the enhancement of presynaptic glutamate release via EP1 receptor activation. In contrast, bicuculline induces allodynia by the blockade of gamma-aminobutyric acid (GABA)A receptor-mediated inhibitory system. As the clinically available analgesics, pregabalin (alpha2delta-subunit calcium channel ligand), ziconotide (N-type calcium channel blocker), mexiletine (sodium channel blocker), and duloxetine (serotonin and norepinephrine reuptake inhibitors) were evaluated in these neurochemically-induced allodynia models. Pregabalin almost completely alleviated NMDA-, PGE2-, and bicuculline-induced allodynia. Despite being classified as an agent with a similar molecular target mechanism, ziconotide could only alleviate PGE2-induced allodynia, but not NMDA- or bicuculline-induced allodynia, as did mexiletine and duloxetine. These results taken together suggest that ziconotide, mexiletine, and duloxetine suppress spinal hyperactivity via the presynaptic site mechanism. In contrast, pregabalin could suppress via the downstream step during spinal hyperactivation such as postsynaptic NMDA activation or dysfunction of GABAergic control in addition to presynaptic mechanism. In conclusion, present findings provide implication that the spinal anti-nociceptive mechanistic site of pregabalin is different from that of ziconotide, mexiletine, and duloxetine, and pregabalin could have a broader anti-nociceptive mechanism other than N-type calcium channel blockade.

Cardioprotective effect of an L/N-type calcium channel blocker in patients with hypertensive heart disease

Left ventricular (LV) diastolic dysfunction is related to increased cardiac sympathetic activity. We investigated the effect of cilnidipine, an L/N-type calcium channel blocker, on LV diastolic function and cardiac sympathetic activity in patients with hypertensive heart disease (HHD) using radionuclide myocardial imaging. Thirty-two frame electrocardiography (ECG) -gated (99m)Tc-sestamibi (MIBI) myocardial single photon emission computed tomography (SPECT), and (123)I-metaiodobenzylguanidine (MIBG) imaging were performed before and 6 months after drug administration in 32 outpatients with HHD. Sixteen of the patients were treated with cilnidipine and the other 16 were treated with nifedipine retard. The parameters for assessing LV diastolic function evaluated using ECG-gated (99m)Tc-MIBI SPECT were peak filling rate (PFR), first-third filling rate (1/3FR), and time to peak filling (TPF). Cardiac sympathetic activity was assessed as early and delayed heart to mediastinum (H/M) ratios and a washout rate (WR), using (123)I-MIBG imaging. The PFR and 1/3FR significantly increased after 6 months of treatment with cilnidipine (p<0.05 for both), but did not with nifedipine retard. The H/M ratios significantly increased (p<0.05 for both) in conjunction with a decreased WR (p<0.05) in the cilnidipine group. Moreover, a significant positive correlation was seen between the rate of change in PFR and the rate of change in early and delayed H/M ratios in the cilnidipine group (p<0.05 for both). The same results were obtained for the relationship between the rate of change in 1/3FR and the rate of change in H/M ratios (p<0.05 for both). However, no such relationship was seen in the nifedipine group. These data indicate that cilnidipine seems to suppress cardiac sympathetic overactivity via blockade of N-type calcium channels and improves LV diastolic function in patients with HHD.

Recent Updates of N-Type Calcium Channel Blockers with Therapeutic Potential for Neuropathic Pain and Stroke

The voltage-dependent N-type calcium channel (Ca(v)2.2), which is distributed in the nerve endings of the central and peripheral nerves, is known to be strongly associated with the pathological processes of cerebral ischemia and neuropathic pain. Ziconotide, the chemically synthesized version of the 25-residue peptide marine toxin omega-conotoxin MVIIA, has been approved as an analgesic drug for severe chronic pain treatment. A blockade of N-type calcium channels has been suggested for reducing the neuronal injury occurring from ischemia/reperfusion events. Therefore, many efforts have been made to develop systemically available small-molecule N-type calcium channel blockers thus far. This review focuses on the latest updates concerning small-molecule N-type calcium channel blockers as potential candidates for the next generation of therapeutics for neuropathic pain and ischemic stroke. The pharmacological advantages of N-type calcium channel blockers in these pathological states are also described.

The Magnitude of α7 Nicotinic Receptor Currents in Rat Hippocampal Neurons Is Dependent upon GABAergic Activity and Depolarization

Hippocampal alpha7(*) nicotinic acetylcholine receptors modulate the release of GABA and glutamate. The control of functional receptor pools by cell firing or synaptic activity could therefore allow for a local adjustment of the sensitivity to cholinergic input upon changes in neuronal activity. We first investigated whether tonic depolarization or cell firing affected the function of alpha7(*). The amplitude of alpha7(*)-gated whole-cell currents in cultured rat hippocampal neurons exposed to high-extracellular K(+) (40 mM KCl) for 24 to 48 h increased 1.3 to 5.5 times. The proportion of alpha7(*)-responsive neurons (99%), the potency of acetylcholine, and the sensitivity to nicotinic antagonists were all unaffected. In contrast, block of spontaneous cell firing with tetrodotoxin for 24 h led to a 37% reduction in mean current amplitude. Reduced alpha7(*) responses were seen after a 24-h blockade of N-type calcium channels but not of L-type calcium channels, N-methyl-d-aspartate (NMDA), or non-NMDA receptor channels, protein kinase C, or calcium-calmodulin kinases II and IV. The N-type or L-type calcium channel antagonists omega-conotoxin GVIA and nifedipine did not prevent the current-potentiating effect of KCl. The GABA(A) antagonist picrotoxin led to a 44% reduction of the currents, despite increasing action potential firing, and also reversed the potentiating effect of KCl. Treatment with GABA, midazolam, or a GABA uptake blocker led to increased currents. These data indicate that alpha7(*)-gated currents in hippocampal neurons are regulated by GABAergic activity and suggest that depolarization-induced GABA release may underlie the effect of increased extracellular KCl.

Constitutive activity of H 3 autoreceptors modulates histamine synthesis in rat brain through the cAMP/PKA pathway

We previously described that agonist-activated histamine H 3 autoreceptors inhibit the stimulation of histamine synthesis mediated by calcium/calmodulin- and cAMP-dependent protein kinases (CaMKII and PKA respectively) in histaminergic nerve endings. In the absence of an agonist H 3 receptors show partial constitutive activity, so we hypothesized that suppression of constitutive activity by an inverse agonist could stimulate these transduction pathways. We show here that the H 3 inverse agonist thioperamide increases histamine synthesis in rat brain cortical slices independently from the amounts of extracellular histamine. Thioperamide effects were mimicked by the inverse agonists clobenpropit and A-331440, but not by the neutral antagonist VUF-5681. In contrast, coincubation with VUF-5681 suppressed thioperamide effects. The effects of thioperamide were completely blocked by the PKA inhibitor peptide myristoyl-PKI 14–22, a peptide that did not block depolarization stimulation of histamine synthesis. In addition, thioperamide effects required depolarization and were impaired by blockade of N-type calcium channels (mediating depolarization), but not by CaMKII inhibition. These results indicate that constitutive activity of H 3 receptors in rat brain cortex inhibits the adenylate cyclase/PKA pathway, and perhaps also the opening of N-type voltage sensitive calcium channels, but apparently not CaMKII.

Pattern-Specific Synaptic Mechanisms in a Multifunctional Network. I. Effects of Alterations in Synapse Strength

Many neuronal networks are multifunctional, producing different patterns of activity in different circumstances, but the mechanisms responsible for this reconfiguration are in many cases unresolved. The mammalian respiratory network is an example of such a system. Normal respiratory activity (eupnea) is periodically interrupted by distinct large-amplitude inspirations known as sighs. Both rhythms originate from a single multifunctional neural network, and both are preserved in the in vitro transverse medullary slice of mice. Here we show that the generation of fictive sighs were more sensitive than eupnea to reductions of excitatory synapse strength caused by either the P/Q-type (alpha1A-containing) calcium channel antagonist omega-agatoxin TK or the non-N-methyl-D-aspartate (NMDA) glutamate receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione (CNQX). In contrast, the NMDA receptor antagonist MK-801, while also inhibiting eupnea, increased the occurrence of sighs. This suggests that among the glutamatergic synapses subserving eupneic rhythmogenesis, there is a specific subset-highly sensitive to agatoxin and insensitive to NMDA receptor blockade-that is essential for sighs. Blockade of N-type calcium channels with omega-conotoxin GVIA also had pattern-specific effects: eupneic activity was not affected, but sigh frequency was increased and postsigh apnea decreased. We hypothesize that N-type (alpha1B) calcium channels selectively coupled to calcium-activated potassium channels contribute to the generation of the postsigh apnea.

Comparison of the Effects of Cilnidipine and Amldipine on Ambulatory Blood Pressure

Cilnidipine is a novel and unique 1,4-dydropyridine derivative calcium antagonist that exerts potent inhibitory actions not only on L-type but also on N-type voltage-dependent calcium channels. Blockade of the neural N-type calcium channel inhibits the secretion of norepinephrine from peripheral neural terminals and depresses sympathetic nervous system activity. The purpose of this study was to assess the effect of cilnidipine and amlodipine on ambulatory blood pressure (BP) levels. We performed 24-h ambulatory BP monitoring before and after once-daily use of cilnidipine (n=55) and amlodipine (n=55) in 110 hypertensive patients. Both drugs significantly reduced clinic and 24-h systolic BP (SBP) and diastolic BP (DBP) (p < 0.005). However, the reductions of 24-h (-1.19+/-6.78 vs. 1.55+/-6.13 bpm, p=0.03), daytime (-1.58+/-6.72 vs. 1.68+/-7.34 bpm, p=0.02) and nighttime (-1.19+/-5.72 vs. 1.89+/-6.56 bpm, p=0.01) pulse rate (PR) were significantly greater in the cilnidipine group than the amlodipine group. There was no correlation between the degree of daytime SBP change and that of daytime PR change after amlodipine treatment (r=-0.08, n.s.), but there was a significant negative correlation between the degree of daytime SBP change and that of day-time PR change after cilnidipine treatment (r=-0.27, p<0.05). N-type calcium channel blockade by cilnidipine may not cause reflex tachycardia, and may be useful for hypertensive treatment.

Cellular Mechanisms Regulating Activity-Dependent Release of Native Brain-Derived Neurotrophic Factor from Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) plays a critical role in activity-dependent modifications of neuronal connectivity and synaptic strength, including establishment of hippocampal long-term potentiation (LTP). To shed light on mechanisms underlying BDNF-dependent synaptic plasticity, the present study was undertaken to characterize release of native BDNF from newborn rat hippocampal neurons in response to physiologically relevant patterns of electrical field stimulation in culture, including tonic stimulation at 5 Hz, bursting stimulation at 25 and 100 Hz, and theta-burst stimulation (TBS). Release was measured using the ELISA in situ technique, developed in our laboratory to quantify secretion of native BDNF without the need to first overexpress the protein to nonphysiological levels. Each stimulation protocol resulted in a significant increase in BDNF release that was tetrodotoxin sensitive and occurred in the absence of glutamate receptor activation. However, 100 Hz tetanus and TBS, stimulus patterns that are most effective in inducing hippocampal LTP, were significantly more effective in releasing native BDNF than lower-frequency stimulation. For all stimulation protocols tested, removal of extracellular calcium, or blockade of N-type calcium channels, prevented BDNF release. Similarly, depletion of intracellular calcium stores with thapsigargin and treatment with dantrolene, an inhibitor of calcium release from caffeine-ryanodine-sensitive stores, markedly inhibited activity-dependent BDNF release. Our results indicate that BDNF release can encode temporal features of hippocampal neuronal activity. The dual requirement for calcium influx through N-type calcium channels and calcium mobilization from intracellular stores strongly implicates a role for calcium-induced calcium release in activity-dependent BDNF secretion.