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Cardiogenic shock associated with calcium-channel and beta blockers: reversal with intravenous calcium chloride.

Two cases in which oral ingestion of beta blocker and slow calcium-channel blocker was associated with profound hypotension and bradycardia are reported, including one case in which serum levels of both drugs were documented in the normal range at a time of severe clinical toxicity. Though unresponsive to usual therapeutic interventions, both patients showed an immediate and dramatic response to intravenous calcium chloride. It is recommended that intravenous calcium chloride be considered in any patient using routine doses of these two agents who presents with hypotension and/or bradycardia.

Adrenergic beta-Antagonists↗

A single Gbeta subunit locus controls cross-talk between protein kinase C and G protein regulation of N-type calcium channels.

The modulation of N-type calcium channels is a key factor in the control of neurotransmitter release. Whereas N-type channels are inhibited by Gbetagamma subunits in a G protein beta-isoform-dependent manner, channel activity is typically stimulated by activation of protein kinase C (PKC). In addition, there is cross-talk among these pathways, such that PKC-dependent phosphorylation of the Gbetagamma target site on the N-type channel antagonizes subsequent G protein inhibition, albeit only for Gbeta(1)-mediated responses. The molecular mechanisms that control this G protein beta subunit subtype-specific regulation have not been described. Here, we show that G protein inhibition of N-type calcium channels is critically dependent on two separate but adjacent approximately 20-amino acid regions of the Gbeta subunit, plus a highly conserved Asn-Tyr-Val motif. These regions are distinct from those implicated previously in Gbetagamma signaling to other effectors such as G protein-coupled inward rectifier potassium channels, phospholipase beta(2), and adenylyl cyclase, thus raising the possibility that the specificity for G protein signaling to calcium channels might rely on unique G protein structural determinants. In addition, we identify a highly specific locus on the Gbeta(1) subunit that serves as a molecular detector of PKC-dependent phosphorylation of the G protein target site on the N-type channel alpha(1) subunit, thus providing for a molecular basis for G protein-PKC cross-talk. Overall, our results significantly advance our understanding of the molecular details underlying the integration of G protein and PKC signaling pathways at the level of the N-type calcium channel alpha(1) subunit.

Amino Acid Sequence↗

Calcium channel blockers for potential impaired fetal growth.

BACKGROUND: Calcium channel blockers may increase the blood flow to the fetus or may improve fetal-placental cellular energy generation. This could enhance fetal growth. OBJECTIVES: The objectives of this review were to assess the effects of calcium channel blockers on fetal growth and neonatal morbidity and mortality in pregnancies where impaired fetal growth is suspected. SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group trials register and the Cochrane Controlled Trials Register. Date of the last search: December 1999. SELECTION CRITERIA: Acceptably controlled trials of calcium channel blockers in women with potential impaired fetal growth. DATA COLLECTION AND ANALYSIS: Eligibility and trial quality were assessed. MAIN RESULTS: One study of 100 women (all smokers) was included. Mean birth weight was significantly higher in women receiving flunarizine compared to the control group. No other significant differences were found. REVIEWER'S CONCLUSIONS: There is not enough evidence to evaluate the use of calcium channel blockers for impaired fetal growth. The apparent beneficial effect of calcium channel blockers on birthweight warrants further investigation.

Calcium Channel Blockers↗

Calcium channels are present in the apical plasma membranes of the hepatopancreatic B-cells of Marsupenaeus japonicus.

This study demonstrates the existence of calcium channels in the apical membranes of the hepatopancreatic blister (B) cells of Marsupenaeus japonicus. Using brush-border membrane vesicles we demonstrated that the channel-mediated calcium passive flux was saturable and was stimulated by a transmembrane electrical potential difference and inhibited by barium. We raised a monoclonal antibody (Mab 24A4) against the calcium channel, which allowed us to inhibit the channel-mediated calcium uptake. By immunocytochemistry, using Mab 24A4, we demonstrated that these channels are located at the apical membrane of hepatopancreatic B cells. Finally, by measuring the calcium uptake in R- and B-enriched cell suspensions, we showed that only the plasma membrane of the B cells expresses a channel-mediated calcium uptake inhibited by barium, verapamil and the monoclonal antibody 24A4. The plasma membrane of R cells did not show calcium channels.

Animals↗

Non-specificity of chloride channel blockers in rat cerebral arteries: block of the L-type calcium channel.

1. The effects of chloride channel blockers on pressure-induced constriction, K(+)-induced force, and whole-cell calcium channel currents were tested in rat cerebral arteries using isobaric and isometric myography, and patch clamp. 2. Under isobaric conditions at 75 mmHg, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a chloride channel blocker, reversibly depressed the myogenic constriction with an IC50 of 32.8 +/- 0.52 microM (mean +/- S.E.M., n = 5). Blockers of Ca(2+)-activated chloride channels, flufenamic acid (100 microM) and 9-anthracene chloride (9-AC; 1 mM), and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel blocker, glibenclamide (100 microM), were without effect in this tissue (n = 3). 3. Under isobaric conditions at 20 mmHg, 37 degrees C, raising [K+]o to 45 mM induced a constriction which was unaffected by 100 microM NPPB (n = 4). In contrast, at 75 mmHg and 18-21 degrees C, 100 microM NPPB completely and reversibly blocked a 45 mM K(+)-induced constriction (n = 3). 4. Under isometric conditions, NPPB reversibly depressed a 45 mM K(+)-induced force with an IC50 of 10.0 +/- 0.76 microM (mean +/- S.E.M., n = 5). Indanyloxyacetic acid 94 (IAA-94), another chloride channel blocker, depressed the K(+)-induced force with an IC50 of 17.0 +/- 1.2 microM (mean +/- S.E.M., n = 4). 5. Using whole-cell patch clamp, 100 microM NPPB or 200 microM IAA-94 blocked calcium channel currents carried by 10 mM Ba2+ by 79.1 +/- 1.7 and 39.8 +/- 7.0%, respectively (mean +/- S.E.M., n = 6). 6. In summary, chloride channel blockers depress calcium channel currents in rat cerebral arteries, which could contribute to a reduction in myogenic contraction.

Animals↗

Multiple voltage-dependent mechanisms potentiate calcium channel activity in hippocampal neurons.

Neuronal voltage-gated calcium channels provide a pathway for calcium influx that is required for processes ranging from intracellular signaling to alterations in cellular excitability. In hippocampal neurons, we have characterized a subtype of dihydropyridine-sensitive L-type calcium channels (Lp channel) that shows multiple kinds of voltage-dependent potentiation of its activity. One type of potentiation is elicited by low-voltage stimuli (-10 mV) and can be seen in dual-pulse protocols in which a transient hyperpolarization is interposed between conditioning and test pulses. The second type of potentiation is elicited by much higher voltages (+60 mV) and is selectively deactivated at hyperpolarized voltages. We have compared these types of potentiation in the Lp channel, the "standard" L-type channel, and the cardiac L-type channel. Our results show that the high-voltage potentiation is common to all three channel types. The low-voltage form of potentiation, however, is unique to the Lp channel. Thus, the Lp channel shows two kinds of potentiation that differ in their voltage dependence and rate of decay. Therefore, calcium channel plasticity in the hippocampus has a variety of forms distinguished by their stimulus requirements and duration.

Animals↗

Interaction of SNARE complexes with P/Q-type calcium channels in rat cerebellar synaptosomes.

P- and Q-type calcium channels, which trigger rapid neurotransmitter release at many mammalian synapses, are blocked by omega-conotoxin MVIIC. 125I-omega-Conotoxin MVIIC binding to rat cerebellar synaptosomes was not displaced by omega-conotoxins GVIA or MVIIA (Ki > 1 microM), which are selective for N-type calcium channels. Solubilized 125I-omega-conotoxin MVIIC receptors were specifically recognized by antibodies directed against alpha1A calcium channel subunits, proteins known to constitute a pore with P/Q-like channel properties. Antibodies against syntaxin 1, SNAP 25, and VAMP 2 (synaptobrevin) each immunoprecipitated a similar fraction (20-40%) of omega-conotoxin MVIIC receptors. Immunoprecipitation was not additive, suggesting that heterotrimeric (SNARE) complexes containing these three proteins interact with P/Q-type calcium channels. Immobilized monoclonal anti-syntaxin antibodies retained alpha1A calcium channel subunits of 220, 180 and 160 kDa monitored by immunoblotting with site directed antibodies. Synaptotagmin was detected in channel-associated complexes, but not synaptophysin, Rab 3A nor rat cysteine string protein. Trimeric SNARE complexes are implicated in calcium-dependent exocytosis, a process thought to be regulated by synaptotagmin. Our results indicate that these proteins interact with P/Q-type calcium channels, which may optimize their location within domains of calcium influx.

Animals↗

Interactions between proteins implicated in exocytosis and voltage-gated calcium channels.

Neurotransmitter release from synaptic vesicles is triggered by voltage-gated calcium influx through P/Q-type or N-type calcium channels. Purification of N-type channels from rat brain synaptosomes initially suggested molecular interactions between calcium channels and two key proteins implicated in exocytosis: synaptotagmin I and syntaxin 1. Co-immunoprecipitation experiments were consistent with the hypothesis that both N- and P/Q-type calcium channels, but not L-type channels, are associated with the 7S complex containing syntaxin 1, SNAP-25, VAMP and synaptotagmin I or II. Immunofluorescence confocal microscopy at the frog neuromuscular junction confirmed that calcium channels, syntaxin 1 and SNAP-25 are co-localized at active zones of the presynaptic plasma membrane where transmitter release occurs. Experiments with recombinant proteins were performed to map synaptic protein interaction sites on the alpha 1A subunit, which forms the pore of the P/Q-type calcium channel. In vitro-translated 35S-synaptotagmin I bound to a site located on the cytoplasmic loop linking homologous domains II and III of the alpha 1A subunit. This direct link would target synaptotagmin, a putative calcium sensor for exocytosis, to a microdomain of calcium influx close to the channel mouth. Cysteine string proteins (CSPs) contain a J-domain characteristic of molecular chaperones that cooperate with Hsp70. They are located on synaptic vesicles and thought to be involved in modulating the activity of presynaptic calcium channels. CSPs were found to bind to the same domain of the calcium channel as synaptotagmin, and also to associate with VAMP. CSPs may act as molecular chaperones in association with Hsp70 to direct assembly or dissociation of multiprotein complexes at the calcium channel.

Animals↗

Anti-aggregatory actions of calcium channel blockers in cat platelets.

Four calcium channel blockers, verapamil, nifedipine, nisoldipine and nimodipine were studied in terms of their ability to inhibit platelet aggregation in cat platelet rich plasma by optical aggregometry. Only verapamil and nisoldipine significantly inhibited aggregation in cat platelets to ADP (2 microM). None of the calcium channel blockers exerted marked inhibition of aggregation induced by 1mM arachidonic acid. However, verapamil produced a moderate but significant inhibition of aggregation to arachidonic acid. Increasing the calcium ion concentration could reverse this inhibition. Thus, there are significant differences in the anti-aggregatory activity of calcium channel blockers in cat platelet rich plasma.

Adenosine Diphosphate↗

Calcium modulation of morphine analgesia: role of calcium channels and intracellular pool calcium.

Calcium (Ca++) administered into the i.c.v. space of mice has been reported to block opioid-induced antinociception dose dependently. These studies were conducted to test the hypothesis that Ca++ i.c.v. blocks the antinociceptive effects of morphine i.c.v. as a consequence of transmembrane Ca++ influx and Ca++ release from intracellular pools. Mice were injected with voltage-sensitive Ca++ channel antagonists at a dose that did not affect morphine antinociception to determine whether this pretreatment would prevent the inhibitory effects of Ca++. Nimodipine (12 nmol i.c.v.) was ineffective in preventing the inhibitory effects of Ca++ (100 nmol i.c.v.), whereas omega-conotoxin GVIA (3.3 pmol i.c.v.) completely prevented the inhibition by Ca++ of morphine antinociception. Other experiments were conducted to determine whether blocking Ca++ release from Ca++/caffeine-sensitive microsomal pools with ryanodine would prevent the inhibitory effects of Ca++. Ryanodine (2 nmol i.c.v.) significantly attenuated the inhibition by Ca++ of morphine antinociception. Another hypothesis to be tested was that stimulation of Ca++ release from intracellular pools would, like Ca++, block morphine antinociception. Thapsigargin (0.002-30 nmol i.c.v.), which increases cytosolic Ca++ by depleting Ca++ from inositol 1,4,5-trisphosphate-sensitive microsomal pools, dose-dependently blocked the antinociceptive effects of morphine. The results of this study indicate that Ca++ blocked morphine antinociception by stimulating Ca++ influx through omega-conotoxin GVIA-sensitive channels and by stimulating Ca++ release from Ca++/caffeine-sensitive microsomal pools.

Animals↗

Differential block of sodium and calcium channels by chlorpromazine in mouse neuroblastoma cells.

1. The effects of chlorpromazine on the voltage-activated sodium and type I (transient) calcium channels were studied in cultured mouse neuroblastoma cells (N1E-115) using the whole-cell patch-clamp technique. 2. Chlorpromazine (2-10 x 10(-6) M) blocked both the sodium channel current and the calcium channel current as carried by Ba2+ in a reversible and dose-dependent manner. 3. The block was not associated with any change in the time course of the activation and inactivation of the sodium and calcium channel currents. 4. The dose-response relationships for the block of these channels measured with a holding potential of -120 mV indicated a 1:1 binding stoichiometry with apparent dissociation constants of 2.5 +/- 10(-6) M and 1.5 +/- 10(-5) M for the sodium and calcium channels, respectively. 5. The block was dependent on the holding potential for both channel currents. The apparent dissociation constant for the sodium channel was decreased to 0.65 +/- 10(-6) M when the membrane was held at -80 mV. The apparent dissociation constant for the calcium channel was decreased to 3.2 +/- 10(-6) M when the membrane was held at -60 mV. 6. The steady-state inactivation curve for the sodium channel was shifted by 12.4 +/- 1.8 mV to more negative potentials by exposure to 1 x 10(-6) M-chlorpromazine. The inactivation curve for the calcium channel was also shifted by 15.4 +/- 3.2 mV to more negative potentials by exposure to 1 x 10(-5) M-chlorpromazine. These results indicate a greater affinity of chlorpromazine for the inactivated state of the channels than for the resting state. 7. Chlorpromazine caused a marked use-dependent block of the sodium channel current, as demonstrated by a cumulative increase of the block during a train of depolarizing pulses. The use-dependent block was observed even with an interpulse interval as long as 2 s. 8. On the other hand, the block of the calcium channel current did not notably accumulate during a train of depolarizing pulses even when extremely prolonged (1 s) pulses were applied at a very short interpulse interval (200 ms). 9. The marked use dependence of the sodium channel block was due to a very slow repriming of the drug-bound sodium channels from inactivation, whereas the lack of use dependence of the calcium channel block was due to a rapid repriming of the drug-bound calcium channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Effects of prolonged ethinyl estradiol treatment on calcium channel binding and in vivo calcium-mediated hemodynamic responses in ovariectomized rats.

Ethinyl estradiol (EE2), administered orally to ovariectomized (ovex) rats, has been shown to prevent loss of bone mineral density and to decrease serum cholesterol levels. Radioligand binding studies with the dihydropyridine (DHP) [3H]PN200-110 were undertaken to characterize calcium (Ca++) channels in cardiac and aortic tissues from ovex rats treated for 35 days with EE2 (0.1 mg/kg day p.o.) or vehicle, and from vehicle-treated sham-operated controls (sham). Cardiac tissues from EE2-treated rats displayed significant increases in the density (Bmax) of high-affinity DHP binding sites (505 +/- 46 fmol/mg) compared with vehicle-treated ovex rats (303 +/- 35 fmol/mg); DHP Bmax values from EE2-treated cardiac tissues were not significantly different from vehicle-treated shams (385 +/- 76 fmol/mg). Cardiac Ca++ efflux channels from sarcoplasmic reticulum were assessed with [3H]ryanodine. [3H]Ryanodine Bmax values were not affected by EE2 treatment. However, [3H]ryanodine Kd values in preparations from EE2-treated rats were significantly decreased (10 +/- 2 nM) compared with ovex rats (35 +/- 11 nM) and were similar to values in sham rats (8 +/- 2 nM). Cardiac beta adrenoceptors were not affected by EE2 treatment, which thus confirmed the selective regulation of DHP receptors by EE2. Aortic preparations from EE2-treated rats exhibited significant increases in DHP receptors (125 +/- 37 fmol/mg) compared with both vehicle-treated ovex rats (32 +/- 3 fmol/mg) and vehicle-treated shams (24 +/- 9 fmol/mg). There were no differences in the binding affinity (Kd) of [3H]PN200-110 for cardiac or aortic sites among the three groups. To ascertain if EE2-mediated increases in Ca++ channel density and ryanodine binding affinity affected in vivo responses to agonists that use extracellular and intracellular Ca++ stores, responses to BAY k 8644 and norepinephrine were examined in pithed rats from the same three groups. No significant differences in hemodynamic responses occurred among the three groups to BAY k 8644 or norepinephrine. Thus, in female ovex rats, prolonged treatment with EE2 resulted in increased density of cardiac and aortic calcium channels which did not translate into increased calcium-mediated inotropic, rate or pressor responses. Conversely, EE2 treatment in ovex rats prevented the decrease in cardiac [3H]ryanodine binding affinity evident in vehicle-treated ovex rats. These data suggest that EE2 treatment in normotensive ovex rats resulted in modulation of both the L-type and sarcoplasmic reticulum Ca++ channels, and these alterations maintained cardiovascular homeostasis.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

Competitive binding experiments reveal differential interactions for dihydropyridine calcium channel activators and antagonists at dihydropyridine receptors on mouse brain membranes.

The binding of the dihydropyridine (+/-)-202-791 and its corresponding calcium channel activating and calcium channel antagonist enantiomers ((+)-S-202-791 and (-)-R-202-791, respectively) to dihydropyridine receptors on mouse brain membranes was studied through competition for [3H]nitrendipine binding and 3H-labelled (+/-)-BAY K8644 ((+/-)-[3H]BAY K8644). Direct binding studies with (+/-)-[3H]BAY K8644 and [3H]nitrendipine revealed high affinity binding to a homogeneous set of dihydropyridine calcium channel activator and antagonist receptors on mouse brain membranes, (+/-)-[3H]BAY K8644 binding to approximately one half as many receptors as did [3H]nitrendipine. Competition binding studies revealed a significant discrimination of both high and low affinity receptors for (-)-R-202-791 and a homogeneous set of receptors for (+)-S-202-791 regardless of whether (+/-)-[3H]BAY K8644 or [3H]nitrendipine was the competing radioligand. Molar ratios (1:1, 5:1, 10:1) of (+)-S-202-792 to (-)-R-202-791 inhibited [3H]nitrendipine binding with displacement binding isotherms substantially different from those predicted on the basis of the binding properties of the individual enantiomers. These data suggest that dihydropyridine calcium channel antagonists and activators bind to different allosterically linked receptors or domains of the dihydropyridine protein associated with the voltage-dependent calcium channels. Furthermore, these results support the concept of multiple binding sites for dihydropyridine ligands.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

Calcium-channel blockers and the elderly.

Calcium-channel blockers may well be the drugs of choice for treating angina, hypertension, and supraventricular arrhythmia in the elderly. They are effective, have no serious side effects, and when wisely matched to the patient, are very well tolerated. Most calcium-channel blockers can be administered once or twice daily. A choice of four is available; only verapamil and diltiazem hydrochloride are useful for supraventricular arrhythmia. All four, however, are effective for the treatment of hypertension and angina. Expanding uses of calcium-channel blockers include peripheral vascular disease and migraine. There may be a theoretical advantage in humans from the point of view of the anti-atherosclerosis demonstrated in animals.

Angina Pectoris↗

Auxiliary subunits: essential components of the voltage-gated calcium channel complex.

Voltage-gated calcium channels are important mediators of several physiological processes, including neuronal excitability and muscle contraction. At the molecular level, the channels are composed of four subunits--the pore forming alpha(1) subunit and the auxiliary alpha(2)delta, beta and gamma subunits. The auxiliary subunits modulate the trafficking and the biophysical properties of the alpha(1) subunit. In the past several years there has been an acceleration of our understanding of the auxiliary subunits, primarily because of their molecular characterization and the availability of spontaneous and targeted mouse mutants. These studies have revealed the crucial role of the subunits in the functional effects that are mediated by voltage-gated calcium channels.

Animals↗

Effects of antagonists to high-threshold calcium channels upon spinal mechanisms of pain, hyperalgesia and allodynia.

High-threshold voltage-dependent calcium channels enable calcium ions to enter neurons upon depolarization and thereby influence synaptic mediator/receptor systems, membrane excitability levels, second and third messenger concentration, and gene expression. These phenomena underlie several processes including those of normal nociception and of hyperalgesia and allodynia. The present article deals with the role of spinal L-, N- and P/Q-type calcium channels in short-lasting nociception as well as in the hyperalgesia and allodynia elicited by chemical irritants of peripheral nociceptors, inflammatory and mechanical lesions of peripheral tissues, and lesions of peripheral nerves. The studies summarized herein are based on the spinal delivery of specific antagonists to high-threshold calcium channels, and reveal that blockade of L-type, P/Q-type and, particularly, N-type channels can prevent, attenuate, or both, subjective pain as well as primary and/or secondary hyperalgesia and allodynia in a variety of experimental and clinical conditions.

Animals↗

Antibodies from ALS patients inhibit dopamine release mediated by L-type calcium channels.

OBJECTIVE: To examine the presence of anti-L-type calcium channel antibodies in the serum of ALS patients. BACKGROUND: Autoimmunity has been hypothesized as one of the mechanisms underlying the pathogenesis of sporadic ALS. Previous studies reported that sera from patients with sporadic ALS contain antibodies against voltage-gated calcium channels (L-type and P-type), but others do not support these findings. METHODS: Regulated secretion of tritiated dopamine ([3H]DA) in PC12 cells is mediated exclusively by calcium entry through L-type calcium channels. To examine whether purified ALS immunoglobulin G (IgG) inhibits [3H]DA release by interfering with calcium entry through L-type calcium channels, evoked release in PC12 cells was determined in the presence of ALS IgG. This functional assay provides a sensitive way to examine L-type calcium channel interaction with IgG from ALS patients. RESULTS: A significant inhibition of depolarization-evoked [3H]DA release (32+/-4%) was observed by purified IgG from ALS patients compared with control subjects (11+/-2%; p < 0.01). Significant inhibition by IgG occurred in 79% (15/19) of the ALS patients compared with only 29% (5/17) in the control group (p < 0.01). The level of calcium channel inhibition by ALS IgG correlated positively with disease duration (r = 0.68; p < 0.01) and correlated negatively with age (r = -0.48; p < 0.05). CONCLUSIONS: These results confirm the presence of antibodies against the L-type calcium channel in the majority of sera from ALS patients, supporting their role in the pathogenesis of ALS.

Amyotrophic Lateral Sclerosis↗

Calcium channel blocker drugs and diabetic control.

Calcium channel blockers are now widely used and there have been case reports of hyperglycemia with nifedipine. In a double-blind, randomized, crossover study of the effects of 4 weeks of therapy, each with two dihydropyridine calcium channel blocker drugs, nifedipine and nicardipine, glucose tolerance, plasma insulin levels, and hemoglobin A1 were assessed in 20 patients with non-insulin-dependent diabetes (mean age 59 years). There was no significant difference in glucose tolerance on active therapy (AUC: control, 548.3 +/- 24.8; nifedipine, 559.3 +/- 41.0; and nicardipine, 589.3 +/- 40.3). Similarly, despite producing significant hemodynamic effects, these drugs produced no significant effect on plasma insulin and hemoglobin A1 levels. Calcium channel blocker drugs may be useful alternatives to thiazide diuretics and beta-blockers in the treatment of ischemic heart disease and hypertension, especially in patients with diabetes.

Adult↗