1
|
Martin V, Vale C, Antelo A, Hirama M, Yamashita S, Vieytes MR, Botana LM. Differential Effects of Ciguatoxin and Maitotoxin in Primary Cultures of Cortical Neurons. Chem Res Toxicol 2014; 27:1387-400. [DOI: 10.1021/tx5000969] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
| | | | | | - Masahiro Hirama
- Department
of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | - Shuji Yamashita
- Department
of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
| | | | | |
Collapse
|
2
|
Marine Toxins Potently Affecting Neurotransmitter Release. MARINE TOXINS AS RESEARCH TOOLS 2009; 46:159-86. [DOI: 10.1007/978-3-540-87895-7_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
|
3
|
Kakizaki A, Takahashi M, Akagi H, Tachikawa E, Yamamoto T, Taira E, Yamakuni T, Ohizumi Y. Ca2+ channel activating action of maitotoxin in cultured brainstem neurons. Eur J Pharmacol 2006; 536:223-31. [PMID: 16581067 DOI: 10.1016/j.ejphar.2006.02.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2006] [Accepted: 02/21/2006] [Indexed: 10/24/2022]
Abstract
The actions of maitotoxin were studied using cultured brainstem cells and adrenal chromaffin cells. Maitotoxin induced a profound increase in the Ca2+ influx into cultured brainstem cells after a brief lag period. The maitotoxin-induced Ca2+ influx was suppressed by various voltage-dependent Ca2+ channel blockers such as Co2+, Mn2+, verapamil and diltiazem. Maitotoxin-catecholamine release in brainstem cells initiated to increase after a lag period of about 1 min and the increase continued even at 4 min after treatment, while in the adrenal chromaffin cells the release started after an about 1-min lag period to attain a maximum within first 2-min and gradually decrease thereafter. These results suggest that maitotoxin acts on Ca2+ channels to increase the Ca2+ influx, accompanied by enhancement of catecholamine release in the brainstem cells with a different temporal profile from that in the adrenal chromaffin cells.
Collapse
Affiliation(s)
- Atsushi Kakizaki
- Department of Pharmaceutical Molecular Biology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
| | | | | | | | | | | | | | | |
Collapse
|
4
|
Porzig H. Pharmacological modulation of voltage-dependent calcium channels in intact cells. Rev Physiol Biochem Pharmacol 2006; 114:209-62. [PMID: 2155471 DOI: 10.1007/bfb0031020] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- H Porzig
- Pharmakologisches Institut, Universität Bern, Switzerland
| |
Collapse
|
5
|
Edwards L, Hessinger DA. Portuguese Man-of-war (Physalia physalis) venom induces calcium influx into cells by permeabilizing plasma membranes. Toxicon 2000; 38:1015-28. [PMID: 10708794 DOI: 10.1016/s0041-0101(99)00213-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Portuguese Man-of-war (Physalia physalis) nematocyst venom dose-dependently stimulates calcium (45Ca(2+)) influx into L-929, GH(4)C(1), FRL, and embryonic chick heart cells. Venom-induced calcium influx is not blocked by ouabain, vanadate, nor organic calcium channel blockers, but is blocked by transition metal cations, such as lanthanum and zinc. Venom-induced calcium influx is accompanied in a dose-dependent manner by the release of intracellular lactate dehydrogenase, indicating a loss in plasma membrane integrity and cytolysis. Concentrations of zinc that block 45Ca(2+) influx also block lactate dehydrogenase release. Lanthanum, which also blocks 45Ca(2+) uptake, does not neutralize the cytolytic activity of the venom, but rather inhibits the venom's cytolytic action at the level of the target cell plasma membrane. Our findings indicate that Man-of-war venom causes an influx of calcium into several different cells types, not just those of the cardiovascular system, and this influx likely occurs by permeabilizing the plasma membranes of cells.
Collapse
Affiliation(s)
- L Edwards
- Department of Physiology and Pharmacology,School of Medicine, Loma Linda University, Loma Linda, CA 92350, USA
| | | |
Collapse
|
6
|
Woods NM, Dixon CJ, Yasumoto T, Cuthbertson KS, Cobbold PH. Maitotoxin-induced free Ca changes in single rat hepatocytes. Cell Signal 1999; 11:805-11. [PMID: 10617283 DOI: 10.1016/s0898-6568(99)00046-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We report the results using bioluminescent and fluorescent indicators to investigate maitotoxin-induced free Ca changes in single rat hepatocytes. Maitotoxin generated a steadily rising free Ca increase after a long lag period. The free Ca increase was dependent on extracellular calcium and could be antagonised by chelation of extracellular calcium or the inclusion of nickel in the superfusate. Manganese-induced quench of cytoplasmic Fura2 dextran revealed an accelerated rate of calcium entry during the final period of the lag phase, immediately prior to the free Ca increase. Imaging experiments demonstrated a markedly different part of free Ca mobilisation compared with glycogenolytic stimuli. Moreover, the use of a combination of hormonal stimuli and maitotoxin revealed that some cells could exhibit free Ca oscillations despite steadily rising intracellular free Ca level. The significance of these observations in terms of the mechanism of action of maitotoxin and the mechanism of free Ca transient generation is discussed.
Collapse
Affiliation(s)
- N M Woods
- Department of Applied Biology, The University of Central Lancashire, Preston, UK.
| | | | | | | | | |
Collapse
|
7
|
Konoki K, Hashimoto M, Murata M, Tachibana K. Maitotoxin-induced calcium influx in erythrocyte ghosts and rat glioma C6 cells, and blockade by gangliosides and other membrane lipids. Chem Res Toxicol 1999; 12:993-1001. [PMID: 10525277 DOI: 10.1021/tx990014m] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Maitotoxin (MTX) at 0.3 nM elicited a 10-20-fold increase in the level of Ca(2+) influx in rat glioma C6 cells. At higher doses (3-30 nM), MTX induced marked Ca(2+) influx in human erythrocyte ghosts when monitored with the fluorescent dye Fura-2. Although the ghosts were not as susceptible to MTX as intact erythrocytes or other cell lines, Fura-2 experiments under various conditions suggested that the MTX-induced entry of ions into the ghosts was mediated by a mechanism similar to that reported for cells or tissues. These ghosts are the simplest system known to be sensitive to MTX and thus may be suitable for research on the direct action of MTX. Gangliosides GM1 and GM3, glycosphingolipids which have a sialic acid residue, strongly inhibited MTX-induced Ca(2+) influx in C6 cells, while the inhibitory action by asialo-GM1, which lacks a sialic acid residue, was somewhat weaker. Their inhibitory potencies were in the following order: GM1 (IC(50) approximately 2 microM) > GM3 (IC(50) approximately 5 microM) > asialo-GM1 (IC(50) approximately 20 microM). GM1 (3 microM) completely blocked MTX (30 nM)-induced Ca(2+) influx in human erythrocyte ghosts. When C6 cells were pretreated with tunicamycin, an antibiotic which inhibits N-linked glycosylation, or concanavalin A, a lectin which exhibits a high affinity for cell-surface oligosaccharides, MTX-induced Ca(2+) influx was significantly potentiated. This suggests that removal of oligosaccharides from the cell surface by tunicamycin or capping of sugar chains on plasma membranes by concanavalin A can potentiate the action of MTX.
Collapse
Affiliation(s)
- K Konoki
- Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | | | | | | |
Collapse
|
8
|
Sorrentino G, Monsurrõ MR, Singh IN, Kanfer JN. Membrane depolarization in LA-N-1 cells. The effect of maitotoxin is Ca(2+)- and Na(+)-dependent. MOLECULAR AND CHEMICAL NEUROPATHOLOGY 1997; 30:199-211. [PMID: 9165486 DOI: 10.1007/bf02815098] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We investigated the influence of ion compositions on the membrane potential in LA-N-1 human neuroblastoma cells using bisoxonol as a potential-sensitive fluorescent dye. The ability of K+, ouabain, veratridine, and maitotoxin to induce membrane depolarization was evaluated. Increasing concentrations of K+ ions from 10 to 50 mM caused a dose-dependent increase of bisoxonol fluorescence, which was completely independent on Na+ and Ca2+. Ouabain (5 mM), an inhibitor of the Na+, K(+)-ATPase, failed to induce membrane depolarization. Veratridine (40 and 100 microM), a Na+ channel activator, only in the presence of 10 micrograms of Leiurus scorpion venom reduced the membrane potential. Maitotoxin (MTX) from 3 to 10 ng/mL depolarized LA-N-1 cells in a dose-dependent manner, and produced a rapid and sustained increase of intracellular free calcium monitored by means of fluorescent probe fura-2. The MTX-induced depolarization and the increase in cytosolic free calcium concentration were dependent on extracellular Ca2+ ions. On the other hand, Na+ ions also seem to be, although only partially, implicated in the MTX effects, since both the blockade of tetrodotoxin (TTX)-sensitive voltage-operated Na+ channels and the removal of Na+ ions were able to reduce the depolarization. In conclusion, our data indicate that the depolarizing action of MTX on LA-N-1 cells is Ca(2+)- and Na(+)-dependent, although the latter only partially, and that this effect is dependent on Ca2+ influx into the cells likely through a voltage-insensitive calcium-entry system.
Collapse
Affiliation(s)
- G Sorrentino
- Institute of Neurological Sciences, Faculty of Medicine, 2nd University of Naples, Italy
| | | | | | | |
Collapse
|
9
|
Kym PR, Hummert KL, Nilsson AG, Lubin M, Katzenellenbogen JA. Bisphenolic compounds that enhance cell cation transport are found in commercial phenol red. J Med Chem 1996; 39:4897-904. [PMID: 8960548 DOI: 10.1021/jm960300k] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We have isolated two bisphenolic compounds (4 and 5) that have a marked effect on K+ and Na+ concentrations in human cells from commercial preparations of the pH indicator dye phenol red (phenolsulfonphthalein). We used a bioassay to identify active chromatographic fractions from the lipophilic impurities present in phenol red, and we determined the structure of two active components (4 and 5) by 1H and 13C NMR and mass spectrometry. When added to human fibroblasts in serum-free medium, the bisphenol fluorene derivative 9,9-bis(4'-hydroxyphenyl)-3-hydroxyfluorene (5) produced a rapid loss of K+ and a gain of Na+, at low concentrations, with an EC50 between 30 and 60 ng/mL (80-160 nM). The 2- and 4-hydroxy isomers of the fluorene 5 (i.e., compounds 6 and 7), prepared by synthesis, had similar activity, although compound 6 was somewhat less potent. The bisphenol xanthene derivative 9,9-bis(4'-hydroxyphenyl)xanthene (4) elicited a similar biological response but was less potent than 5-7; it also had a strong effect on cell adhesion, causing release of cells from the plastic substrate at concentrations as low as 2-5 microg/mL (5.5-14 microM). The structures of xanthene (4) and fluorene (5) bisphenols have been confirmed by synthesis from xanthone and hydroxyfluorenone, respectively, by Friedel-Crafts alkylation with phenol. In the latter case, the desired 3-hydroxyfluorene isomer was formed in situ by rearrangement of the 1-hydroxy isomer.
Collapse
Affiliation(s)
- P R Kym
- Department of Chemistry, University of Illinois, Urbana 61801, USA
| | | | | | | | | |
Collapse
|
10
|
Xi D, Kurtz DT, Ramsdell JS. Maitotoxin-elevated cytosolic free calcium in GH4C1 rat pituitary cells nimodipine-sensitive and -insensitive mechanisms. Biochem Pharmacol 1996; 51:759-69. [PMID: 8602871 DOI: 10.1016/0006-2952(95)02392-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Maitotoxin includes an extracellular Ca2+-dependent membrane depolarization predominantly via activation of L-type voltage-dependent Ca2+ channels (L-VDCC) in GH4C1 rat pituitary cells. In contract to studies employing intracellular dyes, electrophysiological studies have indicated that maitotoxin activates voltage-independent conductances. In the present study, we used fura-2 calcium digital analysis to investigate the actions of very low concentrations of maitotoxin on cytosolic free calcium ([Ca2+]i) in GH4C1 cells in an effort to distinguish different calcium entry mechanisms. Maitotoxin at concentrations as low as 0.01 ng/mL elevated [Ca2+]i 35 +/- 3% and induced membrane depolarization. The concentration dependency for maitotoxin-elevated [Ca2+]i was biphasic with the first phase maximal at 0.05 to 0.5 ng/mL and the minimum EC50 of the second phase about 2.0 ng/mL. Nimodipine (100 nM), a dihydropyridine antagonist of L-VDCC, prevented the [Ca+2]i increase and depolarization induced by up to 0.1 ng/mL maitotoxin, but not at higher concentration (0.5 ng/mL) of maitotoxin. This indicates that lower concentrations (0.1 ng/mL) of maitotoxin require L-VDCC, whereas higher concentrations (>-0.5 ng/mL) of maitotoxin may require additional ionic mechanisms. Maitotoxin (0.5 ng/mL) induced 45Ca2+ uptake and depolarization in Ltk-cells which lack VDCC. Reducing extracellular Cl- from 123 to 5.8 microM increased the magnitude of membrane depolarization by maitotoxin (0.5 ng/mL), which suggests that a Cl- conductance participated in depolarization induced by higher maitotoxin concentrations. Taken together, our results indicate that maitotoxin activates at least two ionic mechanisms. At lower concentrations of maitotoxin, the primary ionic mechanism requires the activation of L-VDCC; however, at higher maitotoxin concentrations, additional ionic mechanisms are involve in the entry of extracellular Ca2+. This latter mechanism may represent the voltage-independent pathway evident under voltage clamp conditions.
Collapse
Affiliation(s)
- D Xi
- Marine Biotoxins Program of the U.S. Marine Fisheries Services, Charleston, SC 29412, USA
| | | | | |
Collapse
|
11
|
Nishio M, Muramatsu I, Yasumoto T. Na(+)-permeable channels induced by maitotoxin in guinea-pig single ventricular cells. Eur J Pharmacol 1996; 297:293-8. [PMID: 8666062 DOI: 10.1016/0014-2999(95)00751-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The characteristics of maitotoxin-induced single channel currents were studied in guinea-pig single ventricular cells using the cell-attached or inside-out configuration of the patch clamp. When the patch electrode was filled with normal Tyrode solution containing 10 nM maitotoxin, elementary currents flowing through the single channel were observed in the cell-attached patch. The amplitude of the single channel current at the resting potential was 1.6 +/- 0.1 pA. The current-voltage relation of the current was linear and the single channel conductance was 16.0 +/- 0.9 pS. The distribution of open times was fitted by a single exponential function (decay time constant: 27 ms), while that of closed times was fitted by the sum of two exponential functions (decay time constants: 1.6 and 34 ms). When the electrode solution was filled with the Ca(2+)-free Tyrode solution, maitotoxin also induced single channel currents with parameters similar to those in the normal Tyrode solution. Under inside-out patch clamp conditions and in 150 mM Na+ solution on both sides of the patch membrane, maitotoxin also induced single channel currents. Choline+ could not substitute for Na+. These results indicate that maitotoxin induces single ionic channels irrespective of the presence or absence of Ca2+ and that the charge carrier of the single channel current is Na+ rather than Ca2+. The increase in Na+ permeability through maitotoxin-induced channels may be possibly responsible for its biological actions.
Collapse
Affiliation(s)
- M Nishio
- Department of Pharmacology, Kanazawa Medical University, Ishikawa, Japan
| | | | | |
Collapse
|
12
|
Narang N, Joseph JA, Ayyagari PV, Gerber M, Crews FT. Age-related loss of cholinergic-muscarinic coupling to PLC: comparison with changes in brain regional PLC subtypes mRNA distribution. Brain Res 1996; 708:143-52. [PMID: 8720870 DOI: 10.1016/0006-8993(95)01272-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Activation of phospholipase C (PLC) coupled to phosphoinositide (PtdIns) hydrolysis occurs through one of the two pathways. One of the major pathways for the neurotransmitter signaling involves phosphoinositide (PtdIns) specific and G-protein dependent PLC-beta, which stimulates the formation of inositol triphosphate (IP3) and inositol tetraphosphate (IP4). Another pathway through the stimulation of calcium influx can directly activate all of the PLC isozymes. At least three isozymes of PLC have been characterized in the brain; PLC-A (alpha), PLC-I (beta) and PLC-II (gamma), which are shown to be localized differentially in brain regions. Muscarinic-cholinergic signals are mediated in large part through the hydrolysis of PtdIns by PLC. To investigate changes in muscarinic coupling to PLC during aging, we examined carbachol stimulated and calcium stimulated PtdIns hydrolysis in cerebral cortical membranes in young, middle aged and old rats. In order to determine whether PtdIns hydrolysis changes correspond to PLC isozyme expression in these animals, we examined three subtypes of PLC mRNA expression in brain sections of young and old rats using in situ hybridization technique. Our study indicated decreased carbachol-induced PLC activity in the cerebral cortex and, in contrast, increased PLC-beta mRNA in the frontal cortex and superficial cortical layer of aged rats. PLC-alpha mRNA was decreased in hippocampal regions of older rats. These studies suggest that during aging there is an uncoupling of muscarinic stimulated PtdIns hydrolysis, which is accompanied by an increased PLC-beta mRNA and decreased PLC-alpha mRNA that may represent compensatory changes in PLC expression.
Collapse
Affiliation(s)
- N Narang
- Neuropsychiatric Research Institute, Fargo, ND 58103, USA
| | | | | | | | | |
Collapse
|
13
|
Prestwich SA, Bolton TB. Inhibition of muscarinic receptor-induced inositol phospholipid hydrolysis by caffeine, beta-adrenoceptors and protein kinase C in intestinal smooth muscle. Br J Pharmacol 1995; 114:602-11. [PMID: 7537591 PMCID: PMC1510025 DOI: 10.1111/j.1476-5381.1995.tb17182.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. The effects of caffeine, isoprenaline, dibutyryl cyclic AMP, isobutylmethylxanthine (IBMX), 12-O-tetradecanoylphorbol-13-acetate (TPA) or 1-oleoyl-2-acetylglycerol (OAG), (protein kinase C (PKC) activators), 2-methoxy verapamil (D600), thapsigargin and ryanodine on muscarinic acetylcholine receptor (AChR)-stimulated inositol phospholipid hydrolysis were studied in smooth muscle fragments from the longitudinal layer of the small intestine of the guinea-pig. 2. Incubation of the fragments with the muscarinic agonist, carbachol (CCh) (100 microM) resulted in rapid increases in the levels of all the inositol phosphate isomers with maximal increases in the [3H]-inositol (1,4,5) trisphosphate ([3H]-Ins(1,4,5)P3) isomer occurring 10 s following incubation. 3. The beta-adrenoceptor agonist, isoprenaline (10 microM) and dibutyryl cyclic AMP (10 microM), a membrane permeant analogue of cyclic AMP both reduced the CCh stimulation, but not the basal levels of [3H]-inositol phosphates. This inhibition by dibutyryl cyclic AMP was enhanced in the presence of the phosphodiesterase inhibitor, IBMX. CCh inhibited the isoprenaline-induced increases in the levels of cyclic AMP and this was via a pertussi toxin (PTX)-sensitive G-protein mechanism. 4. TPA (1 microM) and OAG (100 microM) a 1,2-diacylglycerol (DAG) analogue both reduced the CCh-induced increases in [3H]-inositol phosphates levels but neither affected basal values nor the basal levels of cyclic AMP. 5. D600 (10 microM), which blocks voltage-dependent Ca2+ channels, also reduced the CCh-stimulated levels of [3H]-inositol phosphates suggesting that some of the agonist-induced increases are due to a potentiating effect of Ca2+ entering the cell. 6. Caffeine (0.5-30 mM) significantly inhibited both the basal and CCh-induced increases in all the [3H]-inositol phosphate isomers. Its inhibitory action was not due to increases in cyclic AMP since caffeine had no effect on the levels of cyclic AMP at concentrations up to 30 mM. 7. Incubation with thapsigargin (1 microM) and ryanodine (10 microM) had no effect on either basal or CCh-induced inositol phospholipid hydrolysis or cyclic AMP levels. 8. The results indicate a reciprocal inhibition by beta-adrenoceptors and muscarinic AChRs of their effects on cyclic AMP and inositol phosphate levels respectively. Ca2+ entering the cell (but not the action of ryanodine or thapsigargin) potentiates while caffeine inhibits muscarinic AChR-induced rises in inositol phosphate levels. Diacylglycerols may exert a negative feedback inhibition on inositol phosphate production.
Collapse
MESH Headings
- 1-Methyl-3-isobutylxanthine/pharmacology
- Animals
- Bucladesine/pharmacology
- Caffeine/pharmacology
- Calcium Channels/drug effects
- Calcium-Transporting ATPases/antagonists & inhibitors
- Carbachol/pharmacology
- Cyclic AMP/metabolism
- Diglycerides/pharmacology
- Gallopamil/pharmacology
- Guinea Pigs
- Hydrolysis
- In Vitro Techniques
- Inositol 1,4,5-Trisphosphate/metabolism
- Intestine, Small/drug effects
- Intestine, Small/metabolism
- Isoproterenol/pharmacology
- Muscle, Smooth/drug effects
- Muscle, Smooth/metabolism
- Protein Kinase C/metabolism
- Receptors, Adrenergic, beta/drug effects
- Receptors, Adrenergic, beta/physiology
- Receptors, Muscarinic/drug effects
- Receptors, Muscarinic/metabolism
- Ryanodine/pharmacology
- Stereoisomerism
- Terpenes/pharmacology
- Tetradecanoylphorbol Acetate/pharmacology
- Thapsigargin
Collapse
Affiliation(s)
- S A Prestwich
- Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London
| | | |
Collapse
|
14
|
Young RC, McLaren M, Ramsdell JS. Maitotoxin increases voltage independent chloride and sodium currents in GH4C1 rat pituitary cells. NATURAL TOXINS 1995; 3:419-27. [PMID: 8612004 DOI: 10.1002/nt.2620030604] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Maitotoxin (MTX) is a 3,424 dalton polyether marine toxin that causes influx of calcium through type L voltage-dependent calcium channels (L-VDCC) in GH4C1 rat pituitary cells, presumably as the result of membrane depolarization. In this study we have investigated the ionic conductances responsible for MTX-induced depolarization under voltage clamp conditions using the perforated and ruptured patch methods. MTX-induced steady-state voltage independent currents of nearly 400 pS/pF within seconds of addition to the bath. Ion substitution experiments demonstrated these currents are consistent with the conductance of sodium and chloride, but not calcium, ions. MTX induction of the voltage-independent chloride conductance in GH4C1 cells occurred concurrently without modification of L-VDCC currents. Pretreatment with nimodipine eliminated voltage activation of L-VDCC, and reduced by two thirds the voltage independent current. Analysis as a function of time of MTX exposure revealed that the first 60 sec of MTX-induced currents were not affected by nimodipine pretreatment, but subsequent additional currents were prevented. This indicates that the initial currents induced by MTX occur independently of L-VDCC mediated calcium entry, but full activation of these currents by MTX likely requires the involvement L-VDCC. Taken together this work identifies a voltage-independent sodium/chloride conductance as an initial action of MTX, one that may promote the sequence of ionic events leading to activation of L-VDCC and massive calcium entry.
Collapse
Affiliation(s)
- R C Young
- Department of Obstetrics and Gynecology, Medical University of South Carolina, Charleston 29412, USA
| | | | | |
Collapse
|
15
|
Musgrave IF, Seifert R, Schultz G. Maitotoxin activates cation channels distinct from the receptor-activated non-selective cation channels of HL-60 cells. Biochem J 1994; 301 ( Pt 2):437-41. [PMID: 7519011 PMCID: PMC1137099 DOI: 10.1042/bj3010437] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We investigated whether maitotoxin activates non-selective cation channels, as was recently proposed [Soergel, Yasumoto, Daly and Gusovsky (1992) Mol. Pharmacol. 41, 487-493]. Stimulation of dibutyryl cyclic AMP-differentiated HL-60 cells with the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP; 0.1 microM), the Ca(2+)-ATPase inhibitor thapsigargin (0.1 microM) or maitotoxin (25 ng/ml) resulted in an increase in cytoplasmic free calcium concentration ([Ca2+]i). Unlike fMLP and thapsigargin, maitotoxin produced no increase in [Ca2+]i in the absence of extracellular Ca2+. The increase in [Ca2+]i induced by fMLP was blocked by pretreatment with pertussis toxin (100 ng/ml for 24 h) but not that induced by maitotoxin. Similarly, the increase in [Ca2+]i produced by fMLP but not that produced by maitotoxin was inhibited by pretreatment with phorbol myristate acetate (100 ng/ml). Both fMLP- and maitotoxin-induced increases in [Ca2+]i were blocked by 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenylethyl)-1H-imid azole hydrochloride (SKF 96365) in a concentration-dependent manner. However, the maitotoxin-induced increase in [Ca2+]i was more sensitive to inhibition by SKF 96365 than the fMLP-induced increase. fMLP-induced increases in [Ca2+]i were blocked by cations with Gd3+ being more effective than Cd2+, whereas for maitotoxin Cd2+ was more effective than Gd3+. Both fMLP and thapsigargin stimulated quenching of Fura-2 fluorescence in the presence of extracellular Mn2+, whereas maitotoxin produced no Mn2+ quenching. Taken together these results suggest that maitotoxin does not stimulate the nonselective cation channel activated by fMLP, but instead activates Ca2+ influx by a different mechanism.
Collapse
Affiliation(s)
- I F Musgrave
- Institut für Pharmakologie, Freie Universität Berlin, Germany
| | | | | |
Collapse
|
16
|
Holmes MJ, Lewis RJ. Purification and characterisation of large and small maitotoxins from cultured Gambierdiscus toxicus. NATURAL TOXINS 1994; 2:64-72. [PMID: 8075895 DOI: 10.1002/nt.2620020204] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Three strains of cultured Gambierdiscus toxicus yielded distinct maitotoxins (maitotoxin-1, -2, and -3) which were purified to homogeneity by high pressure liquid chromatography. Maitotoxins-1 and -2 are large toxins (molecular weights for the sodium salts = 3,422 and 3,298, respectively), whereas maitotoxin-3 is relatively small (molecular weight = 1,060 for the sodium salt). The contractile actions on isolated guinea-pig left atria, vas deferens and ilea of maitotoxins-1 and -2 were compared with those of the small maitotoxin, maitotoxin-3. Maitotoxin-1, -2 and -3 each produced quantitatively similar, concentration-dependent patterns of positive and negative inotropy in atria when compared on a mouse unit/ml basis (one mouse unit is the intraperitoneal LD50 dose for a 20 g mouse; the LD50 for maitotoxin-2 = 0.08 microgram/kg). Concentrations of maitotoxin-2 greater than 5 x 10(-13) M caused positive inotropy. The three maitotoxins produced patterns of contractions in vas deferens and ilea that were qualitatively similar, including a period of prominent spike activity in vas deferens. On a mouse unit/ml basis, the order of potency on smooth muscle was maitotoxin-1 > maitotoxin-3 > maitotoxin-2. The contractile responses of smooth muscle to the maitotoxins were followed by an inhibitory phase where control agonist responses could not be elicited. The maitotoxin-induced contractile responses of vas deferens were inhibited by nicardipine but not phentolamine, indicating that in this tissue, each maitotoxin has mainly a direct contractile effect that requires calcium influx through voltage-sensitive calcium channels.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- M J Holmes
- Southern Fisheries Centre, Queensland Department of Primary Industries, Australia
| | | |
Collapse
|
17
|
Nishio M, Kigoshi S, Muramatsu I, Yasumoto T. Ca(2+)- and Na(+)-dependent depolarization induced by maitotoxin in the crayfish giant axon. GENERAL PHARMACOLOGY 1993; 24:1079-83. [PMID: 8270164 DOI: 10.1016/0306-3623(93)90352-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
1. Maitotoxin (MTX) depolarized the membrane of the crayfish giant axon and decreased the amplitude and maximum rate of rise of action potentials in an irreversible manner. 2. The depolarizing action of MTX was attenuated in low Ca (1 mM; 1/10 of normal concentration) solution and was also inhibited by 2 mM Co2+, 300 microM Ni/+, 1 microM nifedipine, 10 microM verapamil or 1 microM tetrodotoxin. 3. These results suggest that the depolarization by MTX in the crayfish giant axon may be related to changes not only in Ca permeability but also in Na permeability, possibly through the modification of existing Na or Ca channels and/or a new type of channel or pore induced by MTX.
Collapse
Affiliation(s)
- M Nishio
- Department of Pharmacology, Fukui Medical School, Japan
| | | | | | | |
Collapse
|
18
|
Watanabe A, Ishida Y, Honda H, Kobayashi M, Ohizumi Y. Ca(2+)-dependent aggregation of rabbit platelets induced by maitotoxin, a potent marine toxin, isolated from a dinoflagellate. Br J Pharmacol 1993; 109:29-36. [PMID: 8495244 PMCID: PMC2175570 DOI: 10.1111/j.1476-5381.1993.tb13527.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. Administration of maitotoxin (MTX), a dinoflagellate toxin, caused aggregation of rabbit washed platelets. The cytosolic Ca2+ concentration ([Ca2+]i), measured by fura-2 fluorescence technique, was also increased by the presence of MTX. Rates of aggregation response and [Ca2+]i-increase were dependent on tested concentrations (3-100 ng ml-1) of the toxin. 2. The MTX-induced platelet aggregation and [Ca2+]i-increase were totally abolished in a Ca(2+)-free solution. The successive administration of Ca2+ in the presence of MTX elicited the aggregation and increase in [Ca2+]i. 3. Ba2+ was capable of substituting for Ca2+ in the MTX-induced platelet aggregation. In the presence of external Ca2+, transition metals, Co2+, Cd2+ and Ni2+, inhibited the aggregation response to MTX. 4. Organic calcium antagonists (verapamil and nifedipine) as well as a cyclo-oxygenase-inhibitor (aspirin) did not apparently inhibit the aggregation response to MTX, except for a high concentration (10(-5) M) of verapamil, while procaine (10 mM) reduced the rate of platelet aggregation. 5. MTX also elicited a release of ATP from platelets, which was abolished in the absence of external Ca2+. 6. In contrast, thrombin 0.5 unit ml-1 could elicit platelet shape change, [Ca2+]i-increase and ATP-release in the absence of external Ca2+. 7. These results suggest that the MTX-induced platelet activation is caused by an enhanced Ca(2+)-influx presumably through voltage-independent Ca2+ channels on the plasma membrane.
Collapse
Affiliation(s)
- A Watanabe
- Department of Pharmaceutical Molecular Biology, Tohoku University, Miyagi, Japan
| | | | | | | | | |
Collapse
|
19
|
Xi D, Van Dolah F, Ramsdell J. Maitotoxin induces a calcium-dependent membrane depolarization in GH4C1 pituitary cells via activation of type L voltage-dependent calcium channels. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)74000-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
20
|
Murata M, Gusovsky F, Yasumoto T, Daly JW. Selective stimulation of Ca2+ flux in cells by maitotoxin. Eur J Pharmacol 1992; 227:43-9. [PMID: 1330638 DOI: 10.1016/0922-4106(92)90140-q] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Maitotoxin elicits a dose-dependent stimulation of 45Ca2+ influx in glioma C6, pheochromocytoma PC12, insulinoma HIT and human blood cells, while having no effect in liposomes. In HIT cells maitotoxin also elicited influx of 86Rb+ greater than 22Na+ greater than 54Mn2+, but the stimulation was far less than for 45Ca2+. Stimulation of 45Ca2+ influx was blocked by Ni2+, Co2+, Cd2+ and Mn2+, and markedly reduced by Ba2+. Divalent cations, in particular Ca2+, Ba2+, Mn2+ and Cd2+, enhanced influx of the monovalent cations 22Na+ and 86Rb+.
Collapse
Affiliation(s)
- M Murata
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892
| | | | | | | |
Collapse
|
21
|
Meucci O, Grimaldi M, Scorziello A, Govoni S, Bergamaschi S, Yasumoto T, Schettini G. Maitotoxin-induced intracellular calcium rise in PC12 cells: involvement of dihydropyridine-sensitive and omega-conotoxin-sensitive calcium channels and phosphoinositide breakdown. J Neurochem 1992; 59:679-88. [PMID: 1378490 DOI: 10.1111/j.1471-4159.1992.tb09422.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The biological activities of maitotoxin are strictly dependent on the extracellular calcium concentration and are always associated with an increase of the free cytosolic calcium level. We tested the effects of voltage-sensitive calcium channel blockers (nicardipine and omega-conotoxin) on maitotoxin-induced intracellular calcium increase, membrane depolarization, and inositol phosphate production in PC12 cells. Maitotoxin dose dependently increased the cytosolic calcium level, as measured by the fluorescent probe fura 2. This effect disappeared in a calcium-free medium; it was still observed in the absence of extracellular sodium and was enhanced by the dihydropyridine calcium agonist Bay K 8644. Nicardipine inhibited the effect of maitotoxin on intracellular calcium concentration in a dose-dependent manner. The maitotoxin-induced calcium rise was also reduced by pretreating cells with omega-conotoxin. Pretreatment of cells with maitotoxin did not modify 125I-omega-conotoxin and [3H]PN 200-110 binding to PC12 membranes. Nicardipine and omega-conotoxin inhibition of maitotoxin-evoked calcium increase was reduced by pertussis toxin pretreatment. Maitotoxin caused a substantial membrane depolarization of PC12 cells as assessed by the fluorescent dye bisoxonol. This effect was reduced by pretreating the cells with either nicardipine or omega-conotoxin and was almost completely abolished by the simultaneous pretreatment with both calcium antagonists. Maitotoxin stimulated inositol phosphate production in a dose-dependent manner. This effect was reduced by pretreating the cells with 1 microM nicardipine and was completely abolished in a calcium-free EGTA-containing medium. The findings on maitotoxin-induced cytosolic calcium rise and membrane depolarization suggest that maitotoxin exerts its action primarily through the activation of voltage-sensitive calcium channels, the increase of inositol phosphate production likely being an effect dependent on calcium influx. The ability of nicardipine and omega-conotoxin to inhibit the effect of maitotoxin on both calcium homeostasis and membrane potential suggests that L- and N-type calcium channel activation is responsible for the influx of calcium following exposure to maitotoxin, and not that a depolarization of unknown nature causes the opening of calcium channels.
Collapse
MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Animals
- Calcium/analysis
- Calcium/metabolism
- Calcium Channel Blockers/pharmacology
- Calcium Channels/drug effects
- Cytosol/chemistry
- Dihydropyridines/pharmacology
- Dose-Response Relationship, Drug
- GTP-Binding Proteins/physiology
- Marine Toxins/pharmacology
- Nicardipine/pharmacology
- Oxocins
- PC12 Cells/chemistry
- PC12 Cells/metabolism
- Peptides, Cyclic/pharmacology
- Pertussis Toxin
- Phosphatidylinositols/metabolism
- Rats
- Sodium/pharmacology
- Tumor Cells, Cultured/chemistry
- Tumor Cells, Cultured/metabolism
- Tumor Cells, Cultured/pathology
- Virulence Factors, Bordetella/pharmacology
- omega-Conotoxins
Collapse
Affiliation(s)
- O Meucci
- Department of Human Communicative Sciences, II School of Medicine, University of Naples, Italy
| | | | | | | | | | | | | |
Collapse
|
22
|
Schmidt BH, Manzoni OJ, Royer M, Bockaert J, Sladeczek FA. Cholinergic inositol phosphate formation in striatal neurons is mediated by distinct mechanisms. Eur J Pharmacol 1991; 206:87-94. [PMID: 2065718 DOI: 10.1016/0922-4106(91)90016-b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In murine striatal neurons devoid of functional synapses (6 days in vitro) the cholinergic agonists carbachol and arecoline evoked dose-dependent inositol phosphate (InsP) responses with mean log EC50s of -4.1 +/- 0.5 and -4.48 +/- 0.1, respectively. Carbachol (1 mM) and arecoline (1 mM) responses were insensitive to tetrodotoxin, a voltage-sensitive Na+ channel blocker, and were blocked by pirenzepine with relatively low affinity (logIC50 = -5.9 +/- 0.3 for the carbachol response and logIC50 = -5.8 +/- 0.3 for the arecoline response). After synaptogenesis (13 days in vitro) the maximal carbachol effect doubled whereas the arecoline response remained unchanged. This additional effect was sensitive to tetrodotoxin and the voltage-dependent Ca2+ channel blocker, omega-conotoxin. The tetrodotoxin-sensitive carbachol response was blocked by lower concentrations of pirenzepine than the tetrodotoxin-insensitive carbachol response. More than 75% of the InsP response evoked by low concentrations of muscarine (1 and 10 microM) was sensitive to tetrodotoxin whereas only 38% of the InsP response stimulated by 1 mM of muscarine could be blocked by tetrodotoxin. These results suggest that there are at least two different mechanisms (depending on the stage of development), activated most probably by two different muscarinic receptors responsible for the carbachol-induced InsP formation in striatal neurons.
Collapse
Affiliation(s)
- B H Schmidt
- Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France
| | | | | | | | | |
Collapse
|
23
|
Murata M, Gusovsky F, Sasaki M, Yokoyama A, Yasumoto T, Daly JW. Effect of maitotoxin analogues on calcium influx and phosphoinositide breakdown in cultured cells. Toxicon 1991; 29:1085-96. [PMID: 1665603 DOI: 10.1016/0041-0101(91)90206-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Maitotoxin (MTX) and the analogues, bis-desulfated-MTX (didesulfo-MTX), mono-desulfated-MTX (monodesulfo-MTX), and hydrogenated-MTX (H-MTX) were examined on 45Ca2+ influx and phosphoinositide breakdown with hamster insulinoma HIT cells and rat glioma C6 cells. The activity of MTX was greatly reduced either by desulfation or by hydrogenation. Didesulfo-MTX weakly stimulated calcium influx in HIT cells, but had no stimulatory effect on either calcium influx or phosphoinositide breakdown in C6 cells. All the analogues inhibited MTX-induced calcium influx in either HIT or C6 cells. Didesulfo-MTX inhibited the calcium influx elicited by 3 ng/ml MTX in C6 cells with an IC50 of 7.0 +/- 0.7 ng/ml. The data suggest that the sulfate groups in MTX are important for stimulation of calcium influx and phosphoinositide breakdown, but are not essential for binding to a receptor-site on cell membranes. Although catalytic reduction of double bonds in MTX reduced activity by nearly 100-fold, a tritiated H-MTX still represents a potential radioligand for identification of MTX-binding sites.
Collapse
Affiliation(s)
- M Murata
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892
| | | | | | | | | | | |
Collapse
|
24
|
Gusovsky F, Daly JW. Maitotoxin: a unique pharmacological tool for research on calcium-dependent mechanisms. Biochem Pharmacol 1990; 39:1633-9. [PMID: 1971510 DOI: 10.1016/0006-2952(90)90105-t] [Citation(s) in RCA: 125] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- F Gusovsky
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892
| | | |
Collapse
|
25
|
Baird JG, Nahorski SR. Increased intracellular calcium stimulates 3H-inositol polyphosphate accumulation in rat cerebral cortical slices. J Neurochem 1990; 54:555-61. [PMID: 2299353 DOI: 10.1111/j.1471-4159.1990.tb01907.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Agents that increase the intracellular Ca2+ concentration have been examined for their ability to stimulate 3H-inositol polyphosphate accumulation in rat cerebral cortex slices. Elevated extracellular K+ levels, the alkaloid sodium channel activator veratrine, the calcium ionophore ionomycin, and the marine toxin maitotoxin were all able to stimulate phosphoinositide metabolism. Certain features appear common to the agents studied. Thus, although [3H]inositol monophosphate, [3H]inositol bisphosphate ([3H]InsP2), and [3H]inositol trisphosphate were all stimulated, a proportionally greater effect was observed on [3H]InsP2 in comparison to stimulation by the muscarinic receptor agonist carbachol. However, only an elevated K+ level stimulated [3H]inositol tetrakisphosphate ([3H]InsP4) accumulation alone or produced marked synergy with carbachol on the formation of this polyphosphate. The results suggest that agents that elevate the cytoplasmic Ca2+ concentration in cerebral cells can increase the hydrolysis of membrane polyphosphoinositides. The pattern of the response differs from that produced by muscarinic receptor agonists and indicate that Ca2(+)-dependent hydrolysis may involve different pools of lipids, phosphoinositidase C enzymes, or both. However, clear differences in the ability of these agents to stimulate InsP4, alone or in the presence of muscarinic agonist, suggest that factors other than a simple elevated intracellular Ca2+ concentration are implicated.
Collapse
Affiliation(s)
- J G Baird
- Department of Pharmacology and Therapeutics, University of Leicester, England
| | | |
Collapse
|
26
|
Santostasi G, Kutty RK, Bartorelli AL, Yasumoto T, Krishna G. Maitotoxin-induced myocardial cell injury: calcium accumulation followed by ATP depletion precedes cell death. Toxicol Appl Pharmacol 1990; 102:164-73. [PMID: 2296767 DOI: 10.1016/0041-008x(90)90093-a] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Maitotoxin, the most potent marine toxin, is known to increase the uptake and the accumulation of Ca2+ into cells, and was used in the present study to investigate the mechanisms of myocardial cell damage induced by Ca2+ overload. In cultured cardiomyocytes, isolated from 2-day-old rats, maitotoxin affected cell viability, as indicated by the leakage of the cytosolic enzyme lactate dehydrogenase (LDH) and of radiolabeled adenine nucleotides into the extracellular medium. Maitotoxin-induced leakage of LDH steadily increased between 30 min and 24 hr, and was preceded by a marked depletion of intracellular ATP. Addition of maitotoxin resulted in a rapid influx of extracellular Ca2+, as detected by preincubating the cells in the presence of 45Ca; this effect evolved in a few minutes, thus preceding the signs of cell death. Cytosolic levels of free Ca2+ ([Ca2+]i) were monitored by loading freshly isolated, suspended cardiomyocytes with the intracellular fluorescent probe fura-2; in these cells, maitotoxin induced a dose-dependent increase in [Ca2+]i, with a lag phase of less than a minute. All these effects of maitotoxin were inhibited by reducing Ca2+ concentration in the culture medium or by incubating the cells with the calcium-channel blocking drug verapamil. It is thus demonstrated that maitotoxin-induced cardiotoxicity is secondary to an inordinate influx of Ca2+ into the cells. It is also suggested that, in those conditions that lead to an inordinate accumulation of Ca2+ into myocardial cells, the unmatched demands of energy and the depletion of ATP play a primary role in the irreversible stage of cell damage.
Collapse
Affiliation(s)
- G Santostasi
- Section on Drug Tissue Interaction, National Heart, Lung and Blood Institute, Bethesda, Maryland
| | | | | | | | | |
Collapse
|
27
|
Schulick A, Gusovsky F, Yasumoto T, Daly JW. Effects of maitotoxin on atrial natriuretic factor-mediated accumulation of cyclic GMP in PC12 cells. Life Sci 1990; 46:671-8. [PMID: 2156121 DOI: 10.1016/0024-3205(90)90071-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Maitotoxin (MTX) activates calcium channels and stimulates phosphoinositide breakdown in pheochromocytoma PC12 cells, while having no effect on basal levels of the cyclic nucleotides cAMP and cGMP. Atrial natriuretic factor (ANF) induces a dose-dependent accumulation of cGMP in PC12 cells through the activation of a membrane bound guanylate cyclase. Effects of ANF on cGMP are independent of extracellular concentrations of calcium. Since agents that activate phosphoinositide breakdown can indirectly affect cyclic nucleotide formation, the effects of MTX on ANF-mediated accumulation of cGMP was studied. MTX induces a dose-dependent inhibition of ANF-mediated accumulation of cGMP. The inhibition by MTX requires the presence of extracellular calcium, but is unaffected by the calcium channel blocker nifedipine. The inhibitory effect of MTX is not mimicked by the calcium ionophore ionomycin. A phorbol ester, PMA, which stimulates protein kinase C, also inhibits ANF-mediated accumulation of cGMP. Sodium nitroprusside induces large accumulations of cGMP in PC12 cells through the stimulation of a soluble guanylate cyclase. Neither MTX nor PMA inhibit nitroprusside-mediated accumulation of cGMP. The results indicate that in PC12 cells, protein kinase C activation, either directly with PMA, and indirectly with MTX through phosphoinositide breakdown and formation of diacylglycerol, leads to inhibition of ANF-mediated, but not nitroprusside-mediated accumulation of cGMP.
Collapse
Affiliation(s)
- A Schulick
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland
| | | | | | | |
Collapse
|
28
|
Affiliation(s)
- A L Harvey
- Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, Scotland
| |
Collapse
|
29
|
Sladeczek F, Kirk CJ, Bockaert J, Schmidt BH. Non classical, multiple-site interaction of [3H]-prazosin with the alpha 1-adrenoceptor of intact BC3H1 cells. Br J Pharmacol 1989; 97:1101-10. [PMID: 2551439 PMCID: PMC1854612 DOI: 10.1111/j.1476-5381.1989.tb12567.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
1. In intact BC3H1 cells the EC50 of noradrenaline (NA) for the inositol phosphate response measured at 37 degrees C (EC50 = 193 nM) was much lower than its apparent dissociation constant (Ki37 degrees C = 83.211 microM) determined at this temperature by [3H]-prazosin binding. 2. After pretreatment of the cells with NA at 37 degrees C for 45 min, the time used in binding assays at this temperature, this difference between EC50 and Ki37 degrees C did not decrease significantly. An agonist-induced reduction in alpha 1-adrenoceptor affinity can therefore not explain the very high Ki37 degrees C value. 3. NA pretreatment at 37 degrees C decreased the number of [3H]-prazosin binding sites (assessed by whole cell binding at 2 degrees C) by only 49%; not by 100%, the value expected if agonist-induced receptor internalization were the origin of the very low Ki37 degrees C. 4. The EC50 of NA for the inositol phosphate response in the presence of 156 pM [3H]-prazosin was 1.841 microM but the IC50 of NA for the inhibition of [3H]-prazosin binding (126 pM) was 316 microM. As there is no alpha 1-adrenoceptor reserve in these cells we propose that at 37 degrees C [3H]-prazosin interacts, not only with the catecholamine recognition site (site 1) of the receptor, but also reacts weakly with another site from which it cannot be directly displaced by catecholamine-like substances (site 2).
Collapse
Affiliation(s)
- F Sladeczek
- Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France
| | | | | | | |
Collapse
|
30
|
Terao K, Ito E, Kakinuma Y, Igarashi K, Kobayashi M, Ohizumi Y, Yasumoto T. Histopathological studies on experimental marine toxin poisoning--4. Pathogenesis of experimental maitotoxin poisoning. Toxicon 1989; 27:979-88. [PMID: 2799840 DOI: 10.1016/0041-0101(89)90148-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Repeated injections of 45 ng/kg of maitotoxin into the peritoneal cavities of male ICR mice resulted in marked atrophy of lymphoid tissues, a reduction of lymphocytes in the circulating blood, reduced immunoglobulin M in serum, and an increase of calcium content in the adrenal glands. A single injection of 200 ng/kg of maitotoxin induced a marked increase in total calcium content of the adrenal glands as well as in plasma cortisol concentration (about seven times control) within 1 hr. In contrast, mice pretreated with CoCl2, a calcium channel inhibitor, and/or adrenalectomized mice, showed no discernible changes in the lymphoid tissues after repeated injections of maitotoxin. It is thus suggested that maitotoxin first stimulates calcium influx in the adrenal glands, which then causes the release of cortisol into the blood. The excess amount of cortisol in serum produces acute involution of the thymus and other lymphoid tissues.
Collapse
Affiliation(s)
- K Terao
- Research Center for Pathogenic Fungi and Microbial Toxicoses, Chiba University, Japan
| | | | | | | | | | | | | |
Collapse
|
31
|
Sladeczek F, Schmidt BH, Cory RN, el Moatassim C, Alonso R, Kirk KL, Kirk CJ, Rouot B, Bockaert J. Complex interactions of agonists with alpha 1-adrenoceptors in intact cells. Br J Pharmacol 1988; 95:1133-40. [PMID: 2905909 PMCID: PMC1854278 DOI: 10.1111/j.1476-5381.1988.tb11748.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
1. The apparent Ki values of (-)-noradrenaline (NA), (+)- and (-)-adrenaline (Ad), phenylephrine and the mono-fluorinated NAs (in position 2, 5 or 6) for alpha 1-adrenoceptors of intact BC3H1 cells labelled with [3H]-prazosin were greatly dependent on the incubation temperature. 2. The EC50 values of these compounds for stimulation of the inositol phosphate (IP) accumulation at 37 degrees C were intermediate between their apparent dissociation constants at 2 degrees C (Ki2 degrees) and at 37 degrees C (Ki37 degrees). 3. The fact that an irreversible blockade of 46% +/- 6% (n = 3) of the [3H]-prazosin binding sites by phenoxybenzamine reduced the maximal IP-formation induced by NA by 57% +/- 5% (n = 3) shows that there is a direct coupling between alpha 1-adrenoceptors and phospholipase C in BC3H1 cells. 4. The Ki37 degrees s of all agonists tested were in the same range (0.1 to 1 mM) and showed no simple correlation with their EC50 values. 5. The Ki2 degrees values for all the agonist correlated linearly with their EC50 values but were about 20-100 times lower than the respective EC50 values (except for the partial agonist methoxamine). In order to explain this difference, we propose that the apparent high affinity in the cold could be due to an [3H]-prazosin-induced alteration of the active site of the alpha 1-adrenoceptor, increasing its apparent affinity for catecholamines.
Collapse
Affiliation(s)
- F Sladeczek
- Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France
| | | | | | | | | | | | | | | | | |
Collapse
|