共查询到20条相似文献,搜索用时 31 毫秒
1.
Mercedes Villarroya Marí a-Teresa De la Fuente Manuela G. L pez Luis Gandí a Antonio G. Garcí a 《European journal of pharmacology》1997,320(2-3):249-257
The effects of ω-toxins and various Ca2+ antagonist subtypes on the 45Ca2+ entry into bovine adrenal medullary chromaffin cells stimulated via nicotinic acetylcholine receptors or via direct depolarization with K+, have been compared. The conditions selected to stimulate the 45Ca2+ entry consisted of a 60-s period of exposure of cells to 100 μM of the nicotinic acetylcholine receptor agonist dimethylphenylpiperazinium or to 70 mM K+. The N-type voltage-dependent Ca2+ channel blockers ω-conotoxin GVIA and MVIIA (1 μM) inhibited 45Ca2+ entry stimulated by dimethylphenylpiperazinium or K+ by around 25–30%. The P-type Ca2+ channel blocker ω-agatoxin IVA (10 nM) did not affect the dimethylphenylpiperazinium nor the K+ responses; 1 μM (Q-channel blockade) inhibited both responses by around 50%. The N/P/Q-type Ca2+ channel blocker ω-conotoxin MVIIC (1 μM) inhibited the K+ evoked 45Ca2+ entry by 70%, while dimethylphenylpiperazinium was blocked by 50% (P<0.001). The L-type Ca2+ channel blockers nifedipine, furnidipine, diltiazem or verapamil (3 μM each) inhibited much more the dimethylphenylpiperazinium than the K+ response. The dimethylphenylpiperazinium signal was blocked 71, 88, 89, and 53%, respectively, by nifedipine, furnidipine, diltiazem and verapamil, and the K+ response by 38, 29, 22, and 10%. Combined ω-conotoxin MVIIC (1 μM) and furnidipine (3 μM) blocked 100% of the K+ evoked 45Ca2+ entry. However, combined ω-conotoxin GVIA (1 μM), and furnidipine left unblocked 50% of the K+ response. The ‘wide spectrum' Ca2+ channel antagonists flunarizine or dotarizine (3 μM each) blocked the dimethylphenylpiperazinium and the K+ responses to a similar extent (50%); cinnarizine (3 μM) inhibited more the dimethylphenylpiperazinium (82%) than the K+ response (21%). At 3 μM, the highly lipophilic β-adrenoceptor antagonist (±)-propranolol, reduced by 68% the dimethylphenylpiperazinium signal and by 23% the K+ signal. Other high lipophilic β-adrenoceptor antagonists such as metoprolol and labetalol, reduced little the dimethylphenylpiperazinium and the K+ responses. The highly lipophilic agent penfluridol blocked the dimethylphenylpiperazinium response by 30% and the K+ response by 50%. One of the least lipophilic compounds tested, (+)-lubeluzole, blocked by 40% the dimethylphenylpiperazinium and the K+ responses. These data are compatible with the idea that the various ω-toxin peptides used to separate pharmacologically the different voltage-dependent Ca2+ channels expressed by neurones, do not block the neuronal nicotinic acetylcholine receptor ion channel. In contrast the L-type Ca2+ channel blockers do block the nicotinic acetylcholine receptor ionophore. Lipophilicity of the compounds is not a requirement for Ca2+ channel or nicotinic acetylcholine receptor blockade. 相似文献
2.
The effects of the organochlorine (OC) liver tumor promoter heptachlor epoxide (HE) and a related non-tumor promoting OC, delta-hexachlorocyclohexane (δ-HCH), on the dynamics of intracellular calcium (Ca2+) were investigated in mouse 1c1c7 hepatoma cells. HE induced a non-capacitative, Ca2+ entry-like phenomenon, which was transient and concentration-dependent with 10 and 50 μM HE. The plasma membrane Ca2+ channel blocker SKF-96365 antagonized this HE-induced Ca2+ entry. δ-HCH failed to induce Ca2+ entry, rather it antagonized the HE-induced Ca2+ entry. Both HE and δ-HCH induced Ca2+ release from endoplasmic reticulum (ER) at treatment concentrations as low as 10 μM; at 50 μM, the former induced 5× as much Ca2+ release as the latter. The HE-induced Ca2+ release from the ER was antagonized using the IP3 receptor/channel blocker xestospongin C, suggesting that HE induces ER Ca2+ release through the IP3 receptor/channel pore. These results show that the effect of HE on cellular Ca2+ mimics that of mitogens such as epidermal and hepatocyte growth factors. They also provide insight into the similarities and differences between tumorigenic and non-tumorigenic OCs, in terms of the mechanisms and the extent of the [Ca2+]i increased by these agents. 相似文献
3.
Fernando Ruiz Mara Dierssen Jesú s Fl rez Marí a A. Hurl 《European journal of pharmacology》1993,240(2-3):155-161
We analyzed the respiratory effects induced by the Ca2+ channel agonist Bay K 8644 and its enantiomers, Bay R 5417 and Bay R 4407, applied to the ventral medullary surface of cats. Bay K 8644 (10 to 100 μg) and Bay R 5417 (50 to 200 μg) elicited a dose-dependent respiratory depression. Naloxone (0.1 mg/kg), but not D-naloxone, reversed these effects, indicating that an endogenous opioid mechanism was involved. Bay R 4407 (100 μg) was ineffective. The respiratory depressant effects induced by Bay K 8644 and its (−) enantiomer were a consequence of their agonist properties on the L-type Ca2+ channel, since (1) the activity of Bay K 8644 was stereospecific, and (2) nimodipine prevented the effect. We suggest that potent activation of Ca2+ channels or other mechanisms by high doses of Ca2+ agonists elicits the release of endogenous opioid peptides in medullary respiration-related structures. 相似文献
4.
The effects of the K+ channel opener cromakalim on phasic contractions induced by noradrenaline and caffeine were studied in the rat isolated mesenteric bed. In the presence of 1.4 mM Ca2+, 1-s pulses of noradrenaline increased the perfusion pressure of the preparation concentration dependently (midpoint at 92 ± 10 μM noradrenaline). Cromakalim (0.3 and 1 μM) inhibited these contractions in a non-competitive manner. Contractions elicited by 1-s pulses of noradrenaline (100 μM) were inhibited by the dihydropyridine Ca2+ antagonist isradipine by maximally 24 ± 1%, indicating that only a minor component of this contraction depended on Ca2+ entry via dihydropyridine-sensitive Ca2+ channels. Cromakalim was a much more effective inhibitor of these contractions (maximum inhibition by 80%, midpoint of the inhibition curve at 171 ± 15 nM). The effect of cromakalim was stereoselective, inhibited by the sulphonylurea glibenclamide, and abolished in partially depolarizing media (KC1 = 35 and 50 mM). In Ca2+-free medium, cromakalim inhibited the contraction induced by noradrenaline (100 μM) by maximally 69 ± 4%, with a midpoint at 58 ± 14 nM. The effect of cromakalim was again stereoselective, inhibited by glibenclamide, and abolished in the presence of 50 mM KC1. Contractions induced by caffeine (10 and 100 μM) were not affected by cromakalim (1 μM). The results indicate that, in rat mesenteric resistance vessels, cromakalim interferes with the ability of noradrenaline, but not caffeine, to mobilize Ca2+ from intracellular stores. The antivasoconstrictor effect of cromakalim against noradrenaline is inhibited by glibenclamide and appears to be linked to the ability of cromakalim to hyperpolarize the cell membrane. 相似文献
5.
We investigated differences in electrophysiological characteristics between peripheral and central N-type Ca2+ channels, containing 1B-a and a1B-c, respectively. In addition, we examined the inhibitory effects of cilnidipine, a dihydropyridine (DHP) derivative, on both channels. Both 1B subunits were transiently expressed in BHK cells, and then analyzed using the whole-cell patch-clamp technique. The current–voltage relationship showed that 1B-c currents were activated at more negative potentials than 1B-a currents. The voltage-dependent steady-state inactivation and activation showed that the V1/2 values for inactivation and activation of 1B-c (−88.5±1.3 and −33.2±1.3 mV) were both significantly more negative than those for 1B-a (−83.3±1.3 and −27.9±2.3 mV). Despite the different electrophysiological characteristics of these two N-type channels, cilnidipine blocked both with similar potency within the range 0.1 to 10 μM. Furthermore, cilnidipine had no effect on the I–V relationships or the steady-state inactivation curves. Our data indicate that the spliced positions of 1B-a and a1B-c may affect not only their voltage-sensing abilities but also the kinetics of channel activation and inactivation. The data also suggest that cilnidipine binds to sites independent of those controlling voltage-sensing and channel kinetics in these 1B subunits. 相似文献
6.
Prolonged exposure to cannabinoids results in desensitization of cannabinoid receptors. Here, we compared the desensitization produced by the partial agonist, Δ9-tetrahydrocannabinol (THC) to that produced by the full agonist Win55,212-2 on cannabinoid-mediated inhibition of glutamatergic synaptic transmission. Synaptic activity between rat hippocampal neurons was determined from network-driven increases in the intracellular Ca2+ concentration ([Ca2+]i spikes). To assess the effects of prolonged treatment, cultures were incubated with cannabinoids, washed in 0.5% fatty-acid-free bovine serum albumin to ensure the removal of the lipophilic drug and then tested for inhibition of [Ca2+]i spiking by Win55,212-2. In control experiments, 0.1 μM Win55,212-2 inhibited [Ca2+]i spiking by 93 ± 5%. Win55,212-2 produced significantly less inhibition of [Ca2+]i spiking following 18–24 h treatment with 1 μM THC (48 ± 5%) or treatment with 1 μM Win55,212-2 (29 ± 6%). Thus, THC produced significantly less functional desensitization than Win55,212-2. The desensitization produced by THC was maximal at 0.3 μM, remained stable between 1 and 7 days of preincubation and shifted the EC50 of acute inhibition by Win55,212-2 from 27 to 251 nM. Differences in the long-term effects of cannabinoid receptor agonists on synaptic transmission may prove important for evaluating their therapeutic and abuse potential. 相似文献
7.
Adenosine has been shown to increase the release of neurotransmitters by stimulation of adenosine A2 receptors. This effect probably depends on Ca2+ entry into presynaptic nerve terminals. In the present work the ability of the mixed adenosine A1/A2 agonist, 2-chloroadenosine, to stimulate Ca2+ uptake into rat brain synaptosomes was investigated. 45Ca2+ uptake was induced by 20 μM veratridine. In the absence of other drugs, 2-chloroadenosine (1 μM) decreased 45Ca2+ uptake into synaptosomes. Blocking the adenosine A1 receptor with 100 nM of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), 2-chloroadenosine (1 μM) increased rather than decreased the uptake of 45Ca2+ into synaptosomes. The excitatory effect of 2-chloroadenosine observed in the presence of DPCPX was reversed by 200 nM of ω-agatoxin-IVA, a specific P-type Ca2+ channel antagonist, but not by L-type (nifedipine, 100 nM to 1 μM; methoxyverapamil 1-10 μM) or N-type (ω-conotoxin GVIA, 500 nM) Ca2+ channel antagonists. The adenosine A2A selective agonist, 2-p-(2-carboxyethyl)-phenethylamino-5′-N-ethyl-carboxamido-adenosine (CGS 21680), did not significantly modify Ca2+ uptake induced by veratridine. In contrast, the selective adenosine A2 receptor agonist, N6-(2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl)-adenosine (DPMA), in concentrations ranging from 10 nM to 1 μM increased Ca2+ uptake induced by veratridine. The selective adenosine A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DPMX) at a concentration of 10 μM antagonized the stimulatory effect of DPMA (0.1 μM) on 45Ca2+ uptake. In conclusion, activation of adenosine A2 receptors increases Ca2+ uptake by synaptosomes depolarized by veratridine, which could explain the increase of neurotransmitter release observed when A2 receptors are activated. 相似文献
8.
The effects of 7-chloro-3,5-dihydro-5-phenyl-1H-4,1-benzothiazepine-2-on (CGP37157), an inhibitor of mitochondrial Na+/Ca2+ exchange, on depolarization-induced intracellular free Ca2+ concentration ([Ca2+]i) transients were studied in cultured rat dorsal root ganglion neurons with indo-1-based microfluorimetry. A characteristic plateau in the recovery phase of the [Ca2+]i transient resulted from mitochondrion-mediated [Ca2+]i buffering. It was blocked by metabolic poisons and was not dependent on extracellular Ca2+. CGP37157 produced a concentration-dependent decrease in the amplitude of the mitochondrion-mediated plateau phase (IC50=4±1 μM). This decrease in [Ca2+]i was followed by an increase in [Ca2+]i upon removal of the drug, suggesting that Ca2+ trapped in the matrix was released when the CGP37157 was removed from the bath. CGP37157 also inhibited depolarization-induced Ca2+ influx at the concentrations required to see effects on [Ca2+]i buffering. Thus, CGP37157 inhibits mitochondrial Na+/Ca2+ exchange and directly inhibits voltage-gated Ca2+ channels, suggesting caution in its use to study [Ca2+]i regulation in intact cells. 相似文献
9.
Amiloride blocks glutamate-operated cationic channels and protects neurons in culture from glutamate-induced death 总被引:4,自引:0,他引:4
The diuretic amiloride has been suggested as a specific inhibitor of T-type neuronal Ca2+ channels. The effects of amiloride on glutamate receptor-gated cationic channels and glutamate-induced, Ca2+-dependent neuronal death were investigated in primary neuronal cultures from neonatal rats. In primary cultures of cerebellar granule neurons of the rat, receiving 50 μM glutamate for 15 min, at 22°C, in the absence of Mg2+, about 80% of neurons were killed in about 24 hr. Exposure of neurons to such a pulse of glutamate, in the presence of various concentrations of amiloride, resulted in a dose-dependent protection from neurotoxicity (EC50 300 μM, complete protection 1 mM). In voltage-clamped cortical and cerebellar neurons of neonatal rats in primary culture, 100 μM amiloride diminished (by about 25%) glutamate- and/or NMDA-evoked cationic currents, recorded in the whole-cell mode. About 80% of the NMDA- (20 μM) stimulated current was inhibited by 700 μM amiloride. The inhibitory effect of amiloride was not voltage-dependent. In outside-out membrane patches, excised from granule cells and held at −50 mV, 100 μM amiloride changed the NMDA-elicited single channel activity into a fast flickering between the open and closed states. The noise analysis of the data revealed that, although resembling the Mg2+-induced flickering, the amiloride-induced channel block was more similar to the effects described for the action of local anaesthetics on the nicotinic cholinergic channel. The pharmacological relevance of this action of amiloride requires further characterization; the data point out the necessity of a cautious use of amiloride in studying neuronal function. 相似文献
10.
Satoko Takizawa Masatoshi Hori Hiroshi Ozaki Hideaki Karaki 《European journal of pharmacology》1993,250(3):431-437
The effects of isoquinoline derivatives, HA1077 (1-[5-isoquinolinesulfonyl]-homopiperazine) and H-7 (1-[5-isoquinoline-sulfonyl]-2-methylpiperazine), on cytosolic Ca2+ levels ([Ca2+]i) and muscle tension were examined in vascular smooth muscle of rat aorta. High K+ (72.7 mM) and norepinephrine (1 μM) induced a sustained contraction with a sustained increase in [Ca2+]i. HA1077 and H-7 (3–10 μM) inhibited the increse in muscle tension more strongly than the increase in [Ca2+]i. Verapamil (10 μM) completely inhibited the increase in [Ca2+]i and the contraction induced by K+ whereas it inhibited the increase in [Ca2+]i more strongly than the contraction due to norepinephrine. The verapamil-insensitive portion of the norepinephrine-induced contraction was inhibited by HA1077 or H-7. In Ca2+-free solution, 0.1 μM norepinephrine induced a transient increase in [Ca2+]i and muscle tension. The transient contraction was inhibited by 10 μM HA1077 or 10 μM H-7 without inhibiting the increase in [Ca2+]i. 12-Deoxyphorbol 13-isobutyrate (DPB) (1 μM) caused a sustained contraction, and this contraction was inhibited by HA1077 and H-7 at similar concentrations needed to inhibit the contractions induced by high K+ or norepinephrine. In rabbit mesenteric artery permeabilized with Staphylococcus aureus -toxin, 100 μM HA1077 and 100 μM H-7 inhibited the contraction induced by 0.3 μM Ca2+. These results suggest that the inhibitory effects of isoquinoline derivatives, HA1077 and H-7, are due to a decrease in [Ca2+]i and in the Ca2+ sensitivity of contractile elemenst in vascular smooth muscle. 相似文献
11.
Oluseye A. Ogunbayo Pei F. Lai Thomas J. Connolly Francesco Michelangeli 《Toxicology in vitro》2008,22(4):943-952
Tetrabromobisphenol A (TBBPA) is a commonly used brominated flame retardant (BFR) utilized to reduce the flammability of a variety of products. Studies have indicated that a number of BFRs are becoming widely distributed within the environment and are bio-accumulating within organisms. There has been much speculation that a variety of phenolic pollutants (including compounds chemically related to TBBPA, such as bisphenol A) may cause endocrine disruption and Ca2+ dysregulation in cells involved in spermatogenesis. In this study we therefore investigate the effects of TBBPA on mouse TM4 Sertoli cells (essential for sperm development). Results show that TBBPA increases Ca2+ within these cells in the 5–60 μM concentration range (EC50, 21 μM). TBBPA also causes cell death (LC50, 18 μM) partly via apoptosis, involving Ca2+-dependent mitochondrial depolarisation. Studies on intracellular Ca2+ transporters shows that TBBPA can inhibit sarcoplasmic/endoplasmic reticulum Ca2+-ATPases (SERCA) at low concentrations (IC50, 0.4 to 1.2 μM) and also activate the Ryanodine receptor Ca2+ channel within the 0.4–4 μM concentration range. Therefore these studies suggest that the cytotoxic effects of TBBPA on cells is partly due to dysregulation of Ca2+ signalling, by directly affecting Ca2+ transport proteins. 相似文献
12.
Resin acids from bleached wood pulp are toxic to fish. 12,14-Dichlorodehydroabietic acid (12,14-Cl2DHA) raises cytoplasmic Ca2+ in synaptosomes and blocks neural GABAA receptors; however, the underlying mechanism remains unclear in these earlier rodent studies. 12,14-Cl2DHA (50 μM) almost completely blocked native GABAA currents (rat cortical cultures) but had no significant effect on picrotoxin-sensitive recombinant human receptors in oocytes (1, β2 and γ2L: the most prevalent isoforms in mammalian brain). In oocytes, 12,14-Cl2DHA failed to produce a calcium-activated chloride current, in contrast to the calcium ionophore ionomycin (10 μM). However, in cultured cortical pyramidal cells, both ionomycin and 12,14-Cl2DHA produced chloride-selective currents of similar magnitude (presumably secondary to Ca2+ release). 12,14-Cl2DHA was unable to stimulate phosphate labelling of [3H]-inositol in mouse synaptosomes, indicating that the study compound does not cause Ca2+ release via an IP3 mechanism. Calcium pump ATPase inhibition also seems unlikely since thapsigargin did not elevate free calcium in synaptosomes. 12,14-Cl2DHA clearly blocks GABAA currents indirectly: we infer that its toxicity may be secondary to the elevations in cytoplasmic Ca2+ via an unidentified recognition site (or receptor) found in neuronal cells. 相似文献
13.
Jun Anabuki Masatoshi Hori Hiroshi Ozaki Iwao Kato Hideaki Karaki 《European journal of pharmacology》1990,190(3):373-379
The mechanism of the vasodilator effect of pinacidil was examined. Pinacidil (0.1–100 μM) inhibited the increases in cytosolic Ca2+ ([Ca2+]i) and muscle tension due to norepinephrine in rat aorta. In contrast, a Ca2+ channel blocker, verapamil, inhibited the norepinephrine-stimulated [Ca2+]i more strongly than the contraction. Higher concentrations of pinacidil (3–100 μM) inhibited the verapamil-insensitive portion of the contraction and [Ca2+]i. An inhibitor of ATP-sensitive K+ channels, glibenclamide, antagonized the inhibitory effect of low concentrations ( 10 pM) of pinacidol. Pinacidil did not change the contraction induced by Ca2+ in vascular smooth muscle permeabilized with Staphylococcus aureus -toxin. Norepinephrine (in the presence of GTP), 12-deoxyphorbol 13-isobutyrate (in the absence of GTP), and treatment with GTPγS potentiated the contraction of permeabilized smooth muscle induced by the addition of Ca2+. Pinacidil (100 μM) inhibited the potentiation due to GTPγS or noepinephrine but not to phorbol ester. These results suggest that pinacidil has dual effects on vascular smooth muscle contraction. At lower concentrations (>0.1 μM), it decreases [Ca2+]i, possibly by activating ATP-sensitive K+ channels. At higher concentrations (> 3 μM), it may additionally inhibit the receptor-mediated, GTP-binding protein-coupled phosphatidyl inositol turnover. 相似文献
14.
Verapamil, diltiazem, nisoldipine and felodipine, calcium antagonist drugs with different chemical structures, were studied for their effects on activities of sarcoplasmic reticulum (SR) isolated from dog cardiac and rabbit skeletal muscles. Nisoldipine and felodipine exerted biphasic actions on both cardiac and skeletal SR Ca2+-ATPase with maximum activation of 40–60% occurring at 20–40 μM for nisoldipine and 30–40% occurring at 15–30 μM for felodipine. At higher drug concentrations, Ca2+-ATPase was inhibited. In the presence of oxalate the maximum activation of the Ca2+ uptake rates at 5–20 μM nisoldipine were 30–50% for cardiac SR and 80–100 μM of the drug were 300–500% for skeletal SR. Felodipine inhibited the rate of Ca2+ uptake by dog cardiac SR, but activated Ca2+ uptake by rabbit skeletal SR with a maximum of 30–50% at 12–25 μM. At higher concentrations of the two drugs the rate of Ca2+ uptake was inhibited. In the absence of oxalate, i.e., limited tranport, nisoldipine shortened the duration of time that Ca2+ was bound to the cardiac and skeletal SR, while the rate of release of Ca2+ from skeletal SR was stimulated. Felodipine at low concentrations similarly caused a premature release of Ca2+ from skeletal SR at a rapid rate; at high concentrations both drugs did not alter Ca2+ binding but delayed Ca2+ release. Unlike nisoldipine and felodipine, verapamil and diltiazem inhibited the rates of Ca2+ transport both in cardiac and skeletal SR. The two drugs inhibited Ca2+-ATPase in cardiac SR but activated the enzyme in skeletal SR. Thus, these drugs caused complex and different effects on cardiac and skeletal SR, possibly resulting from perturbations of the lipid environment of the SR Ca2+-ATPase. 相似文献
15.
The action of phenylalkylamine Ca2+ channel blockers D890 and D888 on Ca2+ uptake and neurotransmitter amino acid release were studied. D890, the quaternary derivative of D600, did not inhibit veratrine-induced 45Ca2+ uptake or the release of neurotransmitter amino acids from rat cerebrocortical synaptosomes, except at high concentrations (200 μM) when it was probably acting extracellularly in a non-specific manner. This contrasted with the more potent (10–50 μM) inhibitory actions of D600 and D888, and may be due to the inability of D890 to cross the synaptic plasma membrane. (−)D888 was shown to cross cell membranes and accumulate in the intracellular compartment of cerebrocortical slices and synaptosomes, where it was associated predominantly with the soluble cytoplasmic fraction. 相似文献
16.
Masahiko Hirafuji Fumito Kawahara Takashi Ebihara Akihiro Nezu Akihiko Tanimura Masaru Minami 《European journal of pharmacology》1999,380(2-3):163-170
The effects of Ni2+, a non-selective cation channel inhibitor, on 5-hydroxytryptamine (5-HT)- and angiotensin II (Ang II)-induced intracellular Ca2+ dynamics in rat aortic smooth muscle cells were investigated. Ni2+ (1 mM) significantly inhibited the transient increase in intracellular Ca2+ concentration ([Ca2+]i) induced by Ang II (100 nM) in aortic smooth muscle cells, as measured using fura-2. However, Ni2+ did not suppress the transient increase in Ca2+ influx induced by 5-HT (10 μM), while significantly suppressed the sustained increase. Ca2+ influx evoked by high KCl (80 mM), thapsigargin (TG) (1 μM) or depletion of intracellular Ca2+ store was almost completely suppressed by Ni2+. Ni2+ had no effect on 5-HT-induced inositol triphosphate production and Ca2+ release from the intracellular store(s). These results suggest that 5-HT, but not Ang II, induces transient Ca2+ influx through Ni2+-insensitive Ca2+ channels, which are distinguishable from the voltage-dependent or store-operated Ca2+ channels. 相似文献
17.
Although small cell lung carcinoma (SCLC) cells express both voltage-gated Ca2+ channels (VGCC) and second messenger-operated Ca2+ channels (SMOCC), little is known about the factors that regulate the activity of these channels in SCLC cells. Ca2+/calmodulin-dependent protein kinase (CaM kinase) type II has been implicated recently in regulating Ca2+ channel activity in other cell types. Because of this, we investigated the effects of the specific CaM kinase antagonist 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tryosyl]-4-phenylpiperazine (KN-62) on Ca2+ channel activity in SCLC cells. Incubation with 10 μM KN-62 for 20 min inhibited depolarization-dependent 45Ca2+ influx by 96.1 ± 2.1% in four independent SCLC cell lines, and by 42.2 ± 6.8% in the NCI-H146 SCLC cell line. Similar inhibitory effects of KN-62 were observed when Fura-2 was used to measure depolarization-dependent Ca2+ influx. These results indicate that KN-62 potently inhibits VGCC activity in SCLC cells. In contrast, KN-62 (10 μM, 20 min) did not inhibit significantly Ca2+ mobilization induced by muscarinic acetylcholine receptor (mAChR) activation in SCLC cells. This indicates that SMOCC are less susceptible than VGCC to inhibition by KN-62 in SCLC cells. Because mAChR activation also inhibits VGCC activity in SCLC cells, we examined the effects of KN-62 on the mAChR-mediated inhibition of VGCC activity. To do this, we measured depolarization-dependent 45Ca2+ influx in SCLC cells incubated with submaximal concentrations of KN-62 and the mAChR agonist carbachol. Treatment of cells with both drugs resulted in almost twice as much inhibition of VGCC activity as in cells treated with only one of the drugs. This indicates that inactivation of CaM kinase with KN-62 does not suppress the ability of mAChR agonists to inhibit VGCC activity. 相似文献
18.
Silvestroni L Rossi F Magnanti M Lubrano C Santiemma V Palleschi S 《Reproductive toxicology (Elmsford, N.Y.)》1999,13(6):445-441
The in vitro effects of the insecticide lindane have been investigated in rat testis peritubular myoid cells (PMCs). Upon PMC exposure to lindane, polarity increase and decrease of dipole dynamics were seen at the membrane level (EC50 20 μM), leading to a partial dissipation of the membrane intrinsic dipole potential. The initial membrane depolarization was increased by Cl− efflux and limited by Ca2+-activated repolarizing currents. Concomitantly, lindane produced an increase in [Ca2+]i (EC50 125 μM) resulting from both Ca2+ release from an inositol 1,4,5-trisphosphate-sensitive intracellular store and a voltage-dependent Ca2+ influx from the extracellular medium. Of particular interest from a toxicologic point of view, insecticide concentrations well below those effective in altering ion homeostasis potently inhibited both [Ca2+]i increase and contraction induced by the natural agonists vasopressin and endothelin-1 (IC50s < 10 μM). These data demonstrate that PMCs are highly susceptible to lindane and suggest that the insecticide may exert testicular toxicity by interfering with hormone-regulated PMC function. 相似文献
19.
Calcineurin is a phosphatase with activity dependent on both Ca2+/calmodulin binding to the catalytic A subunit and Ca2+ binding to the regulatory B subunit. We have previously shown that Pb2+ activates calmodulin with a threshold of about 100 pM free Pb2+, and that Pb2+ and Ca2+ are roughly additive in calmodulin activation (Kern et al., NeuroToxicology 21, 353–364 (2000)). In the present study, we evaluated the effects of Pb2+, with and without Ca2+ and calmodulin, on calcineurin activity. In calmodulin-containing, Ca2+-free solutions, Pb2+ activated calcineurin with a threshold of about 100 pM free Pb2+. Maximum calcineurin activity (comparable to that induced by 10 μM Ca2+) was reached at about 200 pM free Pb2+. Higher Pb2+ concentrations reduced activity, although some activity remained even at 2000 pM free Pb2+. Combined with subsaturating Ca2+ concentrations, as little as 20 pM free Pb2+ enhanced calcineurin activity, but free Pb2+ concentrations greater than 200 pM still reduced activity below maximum. Extremely high Ca2+ concentrations (10 μM) completely reversed the inhibition of activity by 2000 pM free Pb2+. In the absence of calmodulin, Ca2+ slightly stimulated calcineurin activity. Pb2+ did not substitute for Ca2+ in calmodulin-free activation; in fact, high concentrations of Pb2+ inhibited Ca2+-mediated activation. We tentatively conclude that low concentrations of free Pb2+ activate calcineurin by activating calmodulin. Higher concentrations reduce calcineurin activity, perhaps by binding to the B subunit. 相似文献
20.
S. Y. Ge D. Y. Ruan K. Yu J. T. Chen M. Wang G. S. Zhong 《Food and chemical toxicology》2001,39(12):1271-1278
The effects of Fe2+ on the properties of three types of ion channels were studied in acutely dissociated rat hippocampal pyramidal neurons from area CA1 at postnatal ages of 7–14 days using the whole cell patch clamp technique. The results indicated that: (1) in the existence of Fe2+, the activation voltage threshold of transient outward K+ currents (IA) was decreased. The normalized current-voltage curves of activation were well fitted with a single Boltzmann function, and the V1/2 was 2.44±1.14 mV (n=15) in control, whereas 1.79±1.53 (n=15), −2.96±0.92 (n=14), −5.11±1.31 (n=13), −9.05±1.64 mV (n=12) in 1, 10, 100 and 1000 μ
Fe2+, respectively. Differences between two groups were significant (P<0.05, n=12–15), except for that between the control and 1 μ
(P>0.05, n=15). (2) Fe2+ caused a left shift of the current–voltage curves of steady-state inactivation of IA in a concentration-dependent manner. The curves were well fitted with a single Boltzmann function with similar slope (P>0.05, n=10–13). The V1/2 were −70.71±1.23 (n=13), −71.14±1.37 (n=13), −78.21±1.17 (n=11), −84.61±1.34 (n=12), and −89.68±2.59 mV (n=10) in control, 1, 10, 100 and 1000 μ
Fe2+, respectively. Fe2+ also shifted the current–voltage curves of Na+ channel steady-state inactivation to more negative depolarization potentials in parallel, with V1/2, −67.37±1.33 mV (n=12) in control, and −67.52±1.28 mV (n=12), −68.24±1.61 mV (n=10), −71.58±1.45 mV (n=10), −76.65±1.76 mV (n=9) in 1, 10, 100 and 1000 μ
Fe2+ solutions, respectively. (3) In Fe2+ solutions, the recovery from inactivation of IA was slowed. (4) With application of different concentrations of Fe2+, the voltage threshold of activation of delayed rectified outward K+ currents (IK) was decreased, while Fe2+ showed a little inhibition at more positive depolarization. Briefly, the results demonstrated that Fe2+ is a dose- and voltage-dependent, reversible modulator of IA, IK and Na+ channels. The results will be helpful to explain the mechanism of Fe2+ physiological function and Fe2+ intoxication in the central nervous system. 相似文献