Pharmacological evaluation of a new Ca2+ antagonist, 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8): studies in smooth muscles

Basic Calcium Phosphate Crystals Induce Osteoarthritis-Associated Changes in Phenotype Markers in Primary Human Chondrocytes by a Calcium/Calmodulin Kinase 2-Dependent Mechanism

Chondrocytes in osteoarthritis undergo a phenotype shift leading to increased production of cartilage-degrading enzymes. There are similarities between the phenotype of osteoarthritic chondrocytes and those of growth plate chondrocytes. Hydroxyapatite can promote chondrocyte differentiation in the growth plate. Basic calcium phosphate (BCP) crystals (which consist of hydroxyapatite, octacalcium apatite and tricalcium phosphate) are frequently found in osteoarthritic joints. The objective of this study was to determine whether BCP crystals induce disease-associated changes in phenotypic marker expression in chondrocytes. Primary human chondrocytes isolated from macroscopically normal cartilage were treated with BCP for up to 48 h. Expression of indian hedgehog (IHH), matrix metalloproteinase 13 (MMP13), interleukin-6 (IL-6) and type X collagen (COLX) were higher, and expression of sry-box 9 (SOX9) lower, in BCP-treated chondrocytes (50 µg/mL) compared to untreated controls. COLX protein was also present in BCP-treated chondrocytes. Intracellular calcium and levels of phosphorylated and total calcium/calmodulin kinase 2 (CaMK2) were elevated following BCP treatment due to BCP-induced release of calcium from intracellular stores. CaMK2 inhibition or knockdown ameliorated the BCP-induced changes in SOX9, IHH, COLX, IL-6 and MMP13 expression. BCP crystals induce osteoarthritis-associated changes in phenotypic marker expression in chondrocytes by calcium-mediated activation of CaMK2. The presence of BCP crystals in osteoarthritic joints may contribute to disease progression.

Acetyl L-carnitine targets adenosine triphosphate synthase in protecting zebrafish embryos from toxicities induced by verapamil and ketamine: An in vivo assessment

Verapamil is a Ca²⁺ channel blocker and is highly prescribed as an anti-anginal, antiarrhythmic and antihypertensive drug. Ketamine, an antagonist of the Ca²⁺ -permeable N-methyl-d-aspartate-type glutamate receptors, is a pediatric anesthetic. Previously we have shown that acetyl l-carnitine (ALCAR) reverses ketamine-induced attenuation of heart rate and neurotoxicity in zebrafish embryos. Here, we used 48 h post-fertilization zebrafish embryos that were exposed to relevant drugs for 2 or 4 h. Heart beat and overall development were monitored in vivo. In 48 h post-fertilization embryos, 2 mm ketamine reduced heart rate in a 2 or 4 h exposure and 0.5 mm ALCAR neutralized this effect. ALCAR could reverse ketamine's effect, possibly through a compensatory mechanism involving extracellular Ca²⁺ entry through L-type Ca²⁺ channels that ALCAR is known to activate. Hence, we used verapamil to block the L-type Ca²⁺ channels. Verapamil was more potent in attenuating heart rate and inducing morphological defects in the embryos compared to ketamine at specific times of exposure. ALCAR reversed cardiotoxicity and developmental toxicity in the embryos exposed to verapamil or verapamil plus ketamine, even in the presence of 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, an inhibitor of intracellular Ca²⁺ release suggesting that ALCAR acts via effectors downstream of Ca²⁺ . In fact, ALCAR's protective effect was blunted by oligomycin A, an inhibitor of adenosine triphosphate synthase that acts downstream of Ca²⁺ during adenosine triphosphate generation. We have identified, for the first time, using in vivo studies, a downstream effector of ALCAR that is critical in abrogating ketamine- and verapamil-induced developmental toxicities. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Colchicine affects cell motility, pattern formation and stalk cell differentiation in Dictyostelium by altering calcium signaling

Previous work, verified here, showed that colchicine affects Dictyostelium pattern formation, disrupts morphogenesis, inhibits spore differentiation and induces terminal stalk cell differentiation. Here we show that colchicine specifically induces ecmB expression and enhances accumulation of ecmB-expressing cells at the posterior end of multicellular structures. Colchicine did not induce a nuclear translocation of DimB, a DIF-1 responsive transcription factor in vitro. It also induced terminal stalk cell differentiation in a mutant strain that does not produce DIF-1 (dmtA-) and after the treatment of cells with DIF-1 synthesis inhibitor cerulenin (100 μM). This suggests that colchicine induces the differentiation of ecmB-expressing cells independent of DIF-1 production and likely through a signaling pathway that is distinct from the one that is utilized by DIF-1. Depending on concentration, colchicine enhanced random cell motility, but not chemotaxis, by 3-5 fold (10-50 mM colchicine, respectively) through a Ca(2+)-mediated signaling pathway involving phospholipase C, calmodulin and heterotrimeric G proteins. Colchicine's effects were not due to microtubule depolymerization as other microtubule-depolymerizing agents did not have these effects. Finally normal morphogenesis and stalk and spore cell differentiation of cells treated with 10 mM colchicine were rescued through chelation of Ca2+ by BAPTA-AM and EDTA and calmodulin antagonism by W-7 but not PLC inhibition by U-73122. Morphogenesis or spore cell differentiation of cells treated with 50 mM colchicine could not be rescued by the above treatments but terminal stalk cell differentiation was inhibited by BAPTA-AM, EDTA and W-7, but not U-73122. Thus colchicine disrupts morphogenesis and induces stalk cell differentiation through a Ca(2+)-mediated signaling pathway involving specific changes in gene expression and cell motility.

Interaction between uric acid and HMGB1 translocation and release from endothelial cells

We aimed to investigate the potential relationship between alarmins [acting via Toll-like receptor-4 (TLR4)], uric acid (UA), and high-mobility group box-1 protein (HMGB1) during acute kidney injury. UA, which is significantly increased in the circulation following renal ischemia-reperfusion injury (IRI), was used both in vitro and in vivo as an early response-signaling molecule to determine its ability to induce the secretion of HMGB1 from endothelial cells. Treatment of human umbilical vein endothelial cells (HUVEC) with UA resulted in increased HMGB1 mRNA expression, acetylation of nuclear HMGB1, and its subsequent nuclear-cytoplasmic translocation and release into the circulation, as determined by Western blotting and immunofluorescence. Treatment of HUVEC with UA and a calcium mobilization inhibitor (TMB-8) or a MEK/Erk pathway inhibitor (U0126) prevented translocation of HMGB1 from the nucleus, resulting in reduced cytoplasmic and circulating levels of HMGB1. Once released, HMGB1 in autocrine fashion promoted further HMGB1 release while also stimulating NF-κB activity and increased angiopoietin-2 expression and protein release. Transfection of HUVEC with TLR4 small interfering (si) RNA reduced HMGB1 levels during UA and HMGB1 treatment. In summary, UA after IRI mediates the acetylation and release of HMGB1 from endothelial cells by mechanisms that involve calcium mobilization, the MEK/Erk pathway, and activation of TLR4. Once released, HMGB1 promotes its own further cellular release while acting as an autocrine and paracrine to activate both proinflammatory and proreparative mediators.

Effect of the flavonol quercetin on ion transport in the isolated intestine of the eel, Anguilla anguilla

Flavonoids are phenolic compounds used in fish diet formulations for the control of sex differentiation. Consequently it is of interest to know their effects on fish gastrointestinal mucosa that is the first target of these substances after food intake. We studied the effects of the flavonol quercetin on the transepithelial electrical parameters of the isolated intestine of the eel, Anguilla anguilla, by employing Ussing chamber technique. We showed that luminal quercetin (10(-4) M) reduced the serosa negative I(sc) (short circuit current) due to a net Cl- absorption in the control conditions. The reduction of I(sc) was blocked by luminal glybenclamide (10(-4) M). The I(sc) response to the flavonoid was also observed when HCO3- was omitted from the perfusion solutions. The effect of quercetin was nullified by TMB8, a blocker of Ca2+ release from intracellular stores, and was strongly reduced by trifluoroperazine, an inhibitor of calmodulin actions, while it was unmodified by experimental manoeuvres able to alter cytosolic cAMP concentrations. These results suggest that mucosal quercetin stimulated Cl- but not HCO3- secretion; the secretory activity appears to be dependent on the Ca2+-calmodulin system, independent of the cAMP pathway. In addition, this study showed that flavonol mimics the effect of carbachol on the tissue. This conclusion is supported by the following observations: 1) noradrenalin reversed the reduction of I(sc) produced by both carbachol and quercetin; 2) the flavonol was ineffective in tissues in which the muscarinic agonist had already elicited its maximal reduction of I(sc).

Blockade of intracellular calcium release induces an antidepressant-like effect in the mouse forced swimming test

The role of intracellular calcium in the modulation of a depressant-like condition was investigated in the mouse forced swimming test. I.c.v. administration of TMB-8 (0.23-46.3 nmol per mouse), a blocker of Ca2+ release from intracellular stores, decreased the mouse immobility time. I.c.v. injection of thapsigargin (0.003-3 nmol per mouse), compound which selectively inhibits Ca2+ uptake into the endoplasmic reticulum, produced, 60 min after administration, a depressant-like condition. Xestospongin C (1-100 pmol per mouse i.c.v.), an InsP3-receptor antagonist, decreased the mouse immobility time. By contrast, d-myo-inositol (5.4-540 pmol per mouse i.c.v.), compound which produces InsP3, resulted in a depressant-like effect. Similarly, ryanodine (0.1-600 pmol per mouse i.c.v.), an RyR antagonist, decreased the immobility time values whereas the administration of 4-chloro-m-cresol (0.1-100 pmol per mouse i.c.v.), an RyR agonist, showed an opposite effect. The antidepressant-like effects observed with TMB-8, xestospongin C and ryanodine were comparable to that produced by the antidepressant drugs amitriptyline and clomipramine. The treatments employed did not produce any behavioural impairment of mice as revealed by the rota-rod and hole board tests indicating that the antidepressant- and depressant-like effects were not due to a compromised locomotor activity and spontaneous motility of the treated animals. These results indicate that a central variation in intracellular calcium contents is involved in the modulation of a depressive-like condition in the mouse forced swimming test. In particular, the blockade of both InsP3Rs and RyRs appears to play an important role in the induction of an antidepressant-like effect, whereas the stimulation of these receptors is involved in a depressant-like response of mice.

Nitric oxide-induced endoplasmic reticulum stress activates the expression of cargo receptor proteins and alters the glycoprotein transport to the Golgi complex

The endoplasmic reticulum Golgi intermediate compartment 53 protein recycles continuously between the endoplasmic reticulum and the Golgi complex and ensures the anterograde transport of specific glycoproteins with the assistance of the Multiple Clotting Factor Deficiency adaptor protein. Therefore, to analyze the effect of the endoplasmic reticulum stress on the secretory pathway beyond the endoplasmic reticulum, we analyzed the expression of both proteins in J774 macrophages incubated with the nitric oxide donor DETA NONOate or with thapsigargin. Both proteins accumulated progressively, by a transcriptional mechanism, in response to these inducers. Nitric oxide also induced a higher level of calreticulin and glucose regulated 78 protein, two endoplasmic reticulum proteins controlled by the unfolded protein response. Interestingly, nitric oxide induced the processing of the activating transcription factor 6alpha of the unfolded protein response, while thapsigargin also induced the activation of the transcription factor X-box Binding Protein 1. In addition, we showed that the accumulation of both transporters occurred simultaneously with the activation of endoplasmic reticulum-stress-dependent apoptosis, suggesting that these proteins may participate in the events that will eventually decide the fate of the cell. Induction of endoplasmic reticulum stress affected the rate of anterograde transport of a reporter glycoprotein, indicating that the endoplasmic reticulum to Golgi transport is remarkably impaired. Our results indicate that increased levels of cargo receptor proteins might have a function either in the quality control of protein folding in the endoplasmic reticulum or in the homeostasis of the intermediate compartment and Golgi complex during cell stress.

Role of intracellular calcium in acute thermal pain perception

The role of intracellular calcium in acute thermal nociception was investigated in the mouse hot-plate test. Intracerebroventricular (i.c.v.) administration of TMB-8, a blocker of Ca++ release from intracellular stores, produced hypernociception. By contrast, i.c.v. pretreatment with thapsigargin, a depletor of Ca++ intracellular stores, produced an increase of the mouse pain threshold. Furthermore, non-analgesic doses of thapsigargin prevented the hypernociception produced by TMB-8. In mice undergoing treatment with heparin, an InsP3-receptor antagonist, or ryanodine, a ryanodine receptor (RyR) antagonist, a dose-dependent reduction of the pain threshold was observed. Pretreatment with D-myo inositol, compound which produces InsP3, and 4-chloro-m-cresol, a RyR agonist, induced an antinociceptive effect. The heparin hypernociception was prevented by D-myo inositol, but not by L-myo inositol, used as negative control. In the same experimental conditions, the antinociception induced by D-myo inositol was prevented by a non-hyperalgesic dose of heparin. Similarly, the reduction of pain threshold produced by ryanodine was reversed by non-analgesic doses of 4-chloro-m-cresol, whereas the antinocicpetion induced by 4-chloro-m-cresol was prevented by non-hyperalgesic doses of ryanodine. The pharmacological treatments employed did not produce any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate that a variation of intracellular calcium contents at a supraspinal level is involved in the modulation of acute thermal nociception. In particular, the stimulation of both InsP3- and Ry-receptors appears to play an important role in the induction of antinociception in mice, whereas a blockade of these receptors is involved in an hypernociceptive response to acute thermal pain.

Acetyl-L-carnitine requires phospholipase C-IP3 pathway activation to induce antinociception

The cellular events involved in acetyl-L-carnitine (ALCAR) analgesia were investigated in the mouse hot plate test. I.c.v. pretreatment with aODNs against the alpha subunit of G(q) and G(11) proteins prevented the analgesia induced by ALCAR (100 mg kg(-1) s.c. twice daily for 7 days). Administration of the phospholipase C (PLC) inhibitors U-73122 and neomycin, as well as the injection of an aODN complementary to the sequence of PLCbeta(1), antagonized the increase of the pain threshold induced by ALCAR. Pretreatment with U-73343, an analogue of U-73112 inactive on PLC, did not modify ALCAR analgesic effect. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or pretreatment with TMB-8, a blocker of Ca(++) release from intracellular stores, the antinociception induced by ALCAR was dose-dependently antagonized. I.c.v. treatment with heparin, an IP(3) receptor antagonist, prevented the increase of pain threshold induced by the investigated compound, analgesia that was restored by co-administration of D-myo-inositol. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitors calphostin C and cheleritryne, resulted in a dose-dependent potentiation of ALCAR antinociception. The administration of PKC activators, such as PMA and PDBu, dose-dependently prevented the ALCAR-induced increase of pain threshold. Neither aODNs nor pharmacological treatments produced any behavioral impairment of mice as revealed by the rota-rod and hole board tests. These results indicate that central ALCAR analgesia in mice requires the activation of the PLC-IP(3) pathway. By contrast, the simultaneous activation of PKC may represent a pathway of negative modulation of ALCAR antinociception.

H1-receptor stimulation induces hyperalgesia through activation of the phospholipase C-PKC pathway

The supraspinal cellular events involved in H(1)-mediated hyperalgesia were investigated in a condition of acute thermal pain by means of the mouse hot-plate test. I.c.v. administration of the phospholipase C (PLC) inhibitors U-73122 and neomycin antagonized the hyperalgesia induced by the selective H(1) agonist FMPH. By contrast, U-73343, an analogue of U-73122 used as negative control, was unable to modify the reduction of the pain threshold induced by FMPH. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or treatment with heparin, an IP(3)-receptor antagonist, the hyperalgesia induced by the H(1)-receptor agonist remained unchanged. Similarly, pretreatment with D-myo inositol did not alter the H(1)-induced hypernociceptive response. Neither i.c.v. pretreatment with TMB-8, a blocker of Ca(2+) release from intracellular stores, nor pretreatment with thapsigargin, a depletor of Ca(2+) intracellular stores, prevented the decrease of pain threshold induced by FMPH. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitors calphostin C and chelerytrine resulted in a dose-dependent prevention of the H(1)-receptor agonist-induced hyperalgesia. The administration of PKC activators, such as PMA and PDBu, did not produce any effect on FMPH effect. The pharmacological treatments employed did not produce any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate a role for the PLC-PKC pathway in central H(1)-induced hyperalgesia in mice. Furthermore, activation of PLC-IP(3) did not appear to play a major role in the modulation of pain perception by H(1)-receptor agonists.

Nimodipine and TMB-8 potentiate the AMPA-induced lesion in the basal ganglia

Acute injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) into the rat globus pallidus leads to calcium precipitation, neuronal death and gliosis. In order to determine whether L-type calcium channels and/or release of Ca(2+) from intracellular stores contribute to the effects of AMPA, nimodipine and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) were administered in combination with AMPA. Nimodipine, but not TMB-8, tended to exacerbate the calcification process initiated by AMPA; the AMPA/nimodipine/TMB-8 combination produced much more calcium deposition than AMPA (+62%, P<0.05). AMPA alone induced a slight but not significant astroglial reaction. Nimodipine slightly enhanced the astroglial reaction triggered by AMPA, whereas TMB-8 doubled it (P<0.001 versus AMPA). These data suggest that blockade of L-type calcium channels by nimodipine enhances calcium imbalance triggered by AMPA, and the calcium release from the endoplasmic reticulum does not participate in the AMPA-induced calcification.

Effect of interleukin 8 and ICAM-1 on calcium-dependent outflow of K+ in erythrocytes from subjects with essential hypertension

INTRODUCTION

The pathogenic mechanisms underlying the increase in peripheral resistance and the contraction of smooth muscular fibre cells in essential hypertension are not yet clearly understood. However, it is now known that immune system activation plays a role in the pathogenesis of some forms of arterial hypertension, and recent data show that the Ca2+ influx in some cells (i.e. red blood cells, leukocytes, platelets, smooth muscular fibre cells) is increased in subjects with essential hypertension, thus revealing a possible alteration in cellular membrane. The end-points of this study were therefore to ascertain whether red blood cells used as a cellular membrane model have a greater Ca2+ dependent K+ flow (Gardos effect) in hypertensive patients than in normotensive controls, to point out a different regulation of ionic channels, and whether IL-8 and the adhesion molecule ICAM-1 influence the membranous outflow.

MATERIAL AND METHODS

The study was conducted on 87 Caucasian subjects. Of these, 50 (25 men, 25 women; mean age 43 +/- 3 years, mean body mass index (BMI) 27 +/- 0.5 and 22.3 +/- 0.3 kg/m(2), respectively) had mild-to-moderate hypertension (mean arterial blood pressure 120 +/- 8 mmHg ). The other 37 (18 men, 19 women; mean age 39 +/- 3 years; BMI 23.8 +/- 0.5 kg/m(2) and 22.8 +/- 0.5 kg/m(2), respectively were normotensive healthy volunteers (mean arterial blood pressure 89 +/- 2 mmHg). All the patients and subjects were untreated for at least 4 weeks before blood sampling.

RESULTS

Ca2+-dependent K+ outflow was found to be greater in samples from patients with essential hypertension than in those from normotensive controls. lL-8 and ICAM-1 significantly enhanced the Ca2+-dependent K+ outflow in red blood cells from hypertensive subjects but had an inhibitory effect on cells from controls. In the experimental model, the presence of TMB-8, a membrane calcium antagonist, significantly reduced the Ca2+-dependent K+ efflux.

CONCLUSION

Vasoconstriction in subjects with essential hypertension may therefore depend on a different regulation of ionic flow that probably supports an increased Ca2+ inflow in smooth muscle fibre cells. Under certain pathological conditions, some immune system components (i.e. interleukins, adhesion molecules) may directly enhance membrane permeability to Ca2+, thus inducing vasoconstriction in the smooth muscle cells.

The phospholipase C-IP3 pathway is involved in muscarinic antinociception

The cellular events involved in muscarinic analgesia were investigated in the mouse hot-plate test. Intracerebroventricular (i.c.v.) pretreatment with antisense oligonucleotides (aODNs) against the alpha subunit of G(q) and G(11) proteins prevented the analgesia induced by physostigmine and oxotremorine. Furthermore, administration of the phospholipase C (PLC) inhibitor U-73122, as well as the injection of an aODN complementary to the sequence of PLCbeta(1), antagonized the increase of the pain threshold induced by both cholinomimetic drugs. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or treatment with heparin, an IP(3) receptor antagonist, the antinociception induced by physostigmine and oxotremorine was dose-dependently antagonized. I.c.v. pretreatment with TMB-8, a blocker of Ca(2+) release from intracellular stores, prevented the increase of pain threshold induced by the investigated cholinomimetic drugs. Coadministration of Ca(2+) restored the muscarinic analgesia in LiCl, heparin, and TMB-8-preatreated mice. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitor calphostin C, resulted in a dose-dependent enhancement of physostigmine- and oxotremorine-induced antinociception. The administration of PKC activators, such as PMA and PDBu, dose dependently prevented the cholinomimetic drug-induced increase of pain threshold. Neither aODNs nor pharmacological treatments employed produced any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate a role for the PLC-IP(3) pathway in central muscarinic analgesia in mice. Furthermore, activation of PKC by cholinomimetic drugs may represent a pathway of negative modulation of muscarinic antinociception.

Influence of cytisine on catecholamine release in isolated perfused rat adrenal glands

The aim of the present study was to determine the characteristics of cytisine on the secretion of catecholamines (CA) in isolated perfused rat adrenal glands, and to clarify its mechanism of action. The release of CA evoked by the continuous infusion of cytisine (1.5 x 10(-5) M) was time-dependently reduced from 15 min following the initiation of cytisine infusion. Furthermore, upon the repeated injection of cytisine (5 x 10(-5) M), at 30 min intervals into an adrenal vein, the secretion of CA was rapidly decreased following the second injection. Tachyphylaxis to the release of CA was observed by the repeated administration of cytisine. The cytisine-induced secretion of CA was markedly inhibited by pretreatment with chlorisondamine, nicardipine, TMB-8, and the perfusion of Ca2+-free Krebs solution, while it was not affected by pirenzepine or diphenhydramine. Moreover, the secretion of CA evoked by ACh was time-dependently inhibited by the prior perfusion of cytisine (5 x 10(-6) M). Taken together, these experimental data suggest that cytisine causes secretion of catecholamines from the perfused rat adrenal glands in a calcium-dependent fashion through the activation of neuronal nicotinic ACh receptors located in adrenomedullary chromaffin cells. It also seems that the cytisine-evoked release of catecholamine is not relevant to the activation of cholinergic M1-muscarinic or histaminergic receptors.

Agonist-specific and sexual stage-dependent inhibition of gonadotropin-releasing hormone-stimulated gonadotropin and growth hormone release by ryanodine: relationship to sexual stage-dependent caffeine-sensitive hormone release

Differential utilization of intracellular Ca2+ stores with specific functional characteristics could be a potential mechanism for coupling various stimuli to specific cellular responses. In the goldfish pituitary, both gonadotropes and somatotropes possess multiple intracellular Ca2+ stores that are differentially coupled to agonist-evoked exocytosis. We investigated the role of ryanodine receptor/Ca2+-release channels (RyR) in basal and gonadotropin-releasing hormone (GnRH)-evoked hormone secretion from cultured gonadotropes and somatotropes using radioimmunoassay for gonadotropin (GTH-II) and growth hormone (GH). As is the case in vivo, the basal and evoked secretion of both hormones varied with seasonal reproductive status. GnRH-stimulated hormone release was three-fold higher in cells from sexually mature animals compared to those in a sexually regressed state. Nanomolar doses of ryanodine evoked significant GTH-II and GH secretion, suggesting that ryanodine-sensitive Ca2+ stores can couple to exocytosis in both cell types. In gonadotropes, 10 microM ryanodine abolished cGnRH-II-evoked GTH-II release in both sexually mature and sexually regressed fish, while sGnRH signalling was mediated by ryanodine-sensitive Ca2+ stores in cells from sexually regressed fish only. Ryanodine-sensitive Ca2+ stores in somatotropes were only involved in cGnRH-II-stimulated GH release during gonadal regression. In contrast, sGnRH-stimulated, but not cGnRH-II-stimulated, GH release was significantly reduced by 1 microM xestospongin C. Although hormone release stimulated by mobilizing caffeine-sensitive Ca2+ pools was also markedly seasonal, it was largely independent of ryanodine-sensitive Ca2+ stores. Ryanodine-sensitive Ca2+ stores in both cell types are not active downstream of ionomycin, BayK 8644, protein kinase C or cyclic adenosine monophosphate signalling pathways, suggesting difference from a classical Ca2+-induced Ca2+ release system. Ours study is the first to suggest that RyR2 may be involved in the seasonal plasticity of pituitary function, which may be related to cyclic changes observed in reproduction and growth.

Inhibition of cyclic GMP formation and aggregation inDictyosteliumby the intracellular Ca2+antagonist TMB-8

Aggregation in Dictyostelium discoideum was shown in previous studies employing EGTA to require Ca2+, but the intra- or extracellular site of action of this ion and its role in chemotaxis were not determined [1]. In this investigation we show that the intracellular Ca2+ immobilising agent TMB-8 does not affect binding of the signalling nucleotide, cAMP, to the cell surface receptors but abolishes the rapid accumulation of intracellular cGMP and subsequent chemotactic aggregation. We infer that movement of Ca2+ from membrane-bound stores is triggered by binding of cAMP to the cell-surface receptor and that this plays a primary role in stimulating cGMP formation and chemotaxis.

Facilitation of Ca2+ store-dependent noradrenaline release after an N-methyl-D-aspartate receptor antagonist in the rat supraoptic nucleus

We examined the role of N-methyl-d-aspartate (NMDA) receptors in the control of noradrenaline release in the supraoptic nucleus (SON) using a microdialysis method in urethane-anaesthetized rats. Local application of 0.5 mm NMDA into the SON by retrodialysis decreased noradrenaline content in the dialysate from the SON. On the other hand, MK-801, a channel blocker of NMDA receptors, or D(-)2-amino-5-phosphonopentanoic acid (AP-5), a competitive NMDA receptor antagonist, increased the basal noradrenaline content. Tetrodotoxin did not completely block the noradrenaline increase after NMDA antagonists. Infusion of Ca2+-free solution containing Ni2+ and Cd2+, or a mixture of omega-agatoxin IVA and omega-conotoxin GVIA, voltage-sensitive Ca2+ channels blockers, did not block noradrenaline increase after AP-5, but blocked noradrenaline increase after high K+. Infusion of intracellular Ca2+ blockers, thapsigargin or TMB-8, impaired noradrenaline increase after AP-5 but not that after high K+. These data are consistent with the hypothesis that activation of an NMDA receptor inhibits an intracellular Ca2+ store-dependent noradrenaline release from nerve terminals in the SON.

Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor

We have studied whether activation of epidermal growth factor receptor (EGFR) is involved in stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and protein synthesis in cultured rat vascular smooth muscle cells (VSMC). Cyclic stretch (1 Hz) induced a rapid (within 5 min) phosphorylation of ERK1/2, an effect that was time and strength dependent and inhibited by an EGFR kinase inhibitor (AG-1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG-1296). The stretch rapidly (within 2 min) induced tyrosine phosphorylation of several proteins, among which 180-kDa protein was shown to be EGFR as revealed by blockade with AG-1478 as well as immunoprecipitation with anti-EGFR antibody coupled with immunoblotting with anti-phosphotyrosine antibody. The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione-S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies. Transfection of a dominant-negative mutant of H-Ras also inhibited stretch-induced ERK1/2 activation. Treatment with a stretch-activated ion channel blocker (Gd(3+)) and an intracellular Ca(2+) antagonist (TMB-8) inhibited stretch-induced phosphorylation of EGFR and ERK1/2. Treatment with AG-1478 and a mitogen-activated protein kinase kinase inhibitor (PD-98059), but not AG-1296, blocked [(3)H]leucine uptake stimulated by a high level of stretch. These data suggest that ERK1/2 activation by mechanical stretch requires Ca(2+)-sensitive EGFR activation mainly via stretch-activated ion channels, thereby leading to VSMC growth.

Mibefradil-induced inhibition of proliferation of human peripheral blood mononuclear cells

To evaluate the role of intracellular calcium and particularly Ca2+-uptake in the initiation of lymphocyte mitogenesis, the effect of mibefradil, which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels, on the proliferation of human peripheral blood mononuclear cells (PBMCs) is compared with the effect of nifedipine, which blocks only the L-type calcium channel. The rate of [3H]thymidine incorporation into control and concanavalin A-stimulated PBMCs in the presence or absence of the calcium channel blockers mibefradil or nifedipine (1, 10, or 50 microM), and of the intracellular calcium antagonist 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB-8; 1, 10, 25, or 50 microM) was assayed in the cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures also was determined in mibefradil- or nifedipine-treated control or stimulated cells. Restoration of the proliferative response in mibefradil- or nifedipine-treated cells was investigated by addition of exogenous interleukin-2. Interleukin-2-receptor expression in the cells was monitored by using anti-activated T-cell antigen (Tac) antibody, and the interleukin-2 production in the cell supernatants of the cultures was determined by an enzyme-amplified sensitive immunoassay. Mibefradil and nifedipine concentration-dependently reduced the cell number and the [3H]thymidine incorporation or the de novo DNA synthesis in control and concanavalin A-stimulated human PBMCs. Mibefradil exhibited a more pronounced inhibition of the proliferation of human PBMCs than did nifedipine. The inhibitory effect of mibefradil or nifedipine on DNA synthesis was dependent on the timing of treatment with the drugs. The inhibitory effect of mibefradil or nifedipine on the lymphoproliferative response was nearly abolished if the drugs were added 20 h after cell stimulation. A markedly reduced inhibitory effect was found when mibefradil or nifedipine was added 1-7 h after cell stimulation. However, regardless of time of addition, TMB-8 caused a persistent inhibition of the proliferation of human PBMCs. The inhibitory effect of mibefradil or nifedipine on the proliferation of human PBMCs is nearly abolished by addition of the calcium channel activator Bay K 8644. The proliferative response of mibefradil- or nifedipine-treated cells is restored by addition of exogenous interleukin-2. The normal expression of interleukin-2 receptors was preserved, whereas the interleukin-2 production was blocked in the presence of mibefradil or nifedipine. Our data show that mibefradil has a more pronounced inhibitory effect on the proliferation of human PBMCs than nifedipine and that this inhibitory effect on DNA synthesis is dependent on the timing of treatment with both drugs.

Prostaglandin production by guinea-pig endometrial cells: effects of caffeine and other modulators of intracellular calcium

The glandular epithelial cells were found to be the main source of PGF2 alpha (the uterine luteolytic hormone) in guinea-pig endometrium. There was a selective increase in PGF2 alpha production by these cells in culture at the time of the cycle (i.e. day 15) at which there is increased PGF2 alpha release from the guinea-pig uterus in vivo. TMB-8 (an intracellular calcium antagonist), W-7, trifluoperazine (both calmodulin antagonists), thapsigargin (an inhibitor of intracellular calcium uptake) and berberine (an inhibitor of calcium release) reduced the output of PGF2 alpha from day 7 glandular epithelial cells indicating that intracellular calcium is necessary for PGF2 alpha production by these cells. In contrast to its stimulatory effect on PGF2 alpha output from the guinea-pig uterus superfused in vitro and guinea-pig endometrium in culture, caffeine inhibited the output of PGF2 alpha from guinea-pig glandular epithelial cells in culture. Its effect was not fully shared by theophylline, nor mimicked by forskolin showing that cyclic AMP is not involved. The inhibitory actions of caffeine and those of the compounds which interfere with the action of intracellular calcium were not additive, suggesting that caffeine modulates the action of intracellular calcium in some way. Caffeine reduced the intracellular free calcium concentration in endometrial cells, but it was not particularly effective in this respect on day 7 glandular epithelial cells. Caffeine may therefore modulate the action of intracellular calcium in some other way.

Vasodilation Effects and Action Mechanisms of TMB-8 on Basilar Artery in Rabbits

BACKGROUND: 8-(N,N'-diethylamino)-n-octyl-3,4,5-trimethoxybenzoate (TMB-8) is a potent Ca(2+)-antagonist that can prevent/treat ischemic stroke and inhibit the contractility of smooth, skeletal, and cardiac muscles. Further studies are warranted to elucidate the efficacy of TMB-8 on rabbit basilar artery preparation and its action mechanisms on vascular smooth muscle cell cultures. METHODS AND RESULTS: Effects of TMB-8 on the contractility of rabbit's basilar artery in vitro and those on intracellular free Ca(2+) concentrations, [Ca(2+)](i), were studies with isolated organ bath and Fura-2 methods. Histamine-induced concentration-response curves were shifted by TMB-8 in a mixed manner whereas those of norepinephrine and KCl were shifted in a non-competitive manner. In the presence of nifedipine or in a Ca(2+)-free medium, 2,5-di(tert-butyl)-1,4-benzohydroquinone (BHQ) (10 µM) induced an immediate transient contraction in rabbit basilar artery, whereas ryanodine showed a slow, weak, sustained contraction, followed by a weak, sustained relaxation. TMB-8 (30 µM) significantly inhibited these contractions of BHQ and ryanodine. Further, aminophylline enhanced the inhibitory action of TMB-8 on vasocontractions, suggesting that TMB-8's inhibitory actions may be related to the increase of cAMP level. The muscle contraction induced by BHQ was enhanced by pretreatment of the artery ring with TMB-8 for 15 minutes and then TMB-8 was rinsed out. These results indicate that TMB-8 pretreatment can increase Ca(2+) sequestration into sarcoplasmic reticulum, which leads to a larger subsequent Ca(2+) release by BHQ. KCl-induced increase of [Ca(2+)](i) in vascular smooth muscle cells was reduced when the cells were bathed in the medium containing nifedipine. TMB-8 made further reduction on KCl-induced [Ca(2+)](i) increase in nifedipine-containing solution, which had already blocked the voltage-operated Ca(2+) entry. CONCLUSION: These results indicate that (a) TMB-8 can enhance Ca(2+) sequestration into sarcoplasmic reticulum, which leads to a larger amount of Ca(2+) that can be released by BHQ; (b) TMB-8 can inhibit KCl-induced muscle contraction caused by the reduction of [Ca(2+)](i) through saturation of Ca(2+) inside the sarcoplasmic reticulum rather than a direct blockade of Ca(2+)-influx at cell membrane site; and (c) TMB-8 increases cAMP, which enhances Ca(2+) uptake into the sarcoplasmic reticulum.

Regulation of phosphoinositide cycle by intracellular sodium in the blood-brain barrier

In the present study of cerebral microvessels, we report that monensin, a Na+ ionophore, elicits a decrease in 32P radioactivity incorporation into phosphoinositides in cerebral microvessels. In addition, monensin evokes enhanced production of inositol-1-monophosphate (IP) and inositol-1,4-bisphosphate (IP2), together with an increase in the diacylglycerol (DAG) mass. These results indicate that monensin evokes a phosphoinositide hydrolysis by phospholipase C (PLC). The absence of inositol-1,4,5-trisphosphate (IP3) production leads us to think that although phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis occurs in this process, there is a very rapid disappearance of IP3. The net decrease in 32P radioactivity incorporated into phosphoinositides suggests that a partial inhibition of their re-synthesis is also evoked. Experimental evidence with pharmacological tools suggests that: (1) these effects are secondary to an increase in Ca2+ through the Na+/Ca2+ exchanger; and (2) the intracellular Ca2+ release is not involved in these effects of monensin. Since some neuropeptide receptors in cerebral microvessels have been reported to be coupled to either the Na+/H+ exchanger or to PLC, we discuss the possibility that cross-talk exists between these intracellular signalling pathways (phosphoinositide metabolism and Na+ transport) in the blood-brain barrier (BBB).

Segmental heterogeneity of swelling-induced Cl- transport in rat small intestine

The effect of cell swelling induced by hypotonic media was studied in segments of rat small intestine. In the Ussing chamber, exposure to a hypotonic medium caused a decrease in short-circuit current (Isc) and potential difference (Vms) in the jejunum, whereas the ileum responded with an increase in Isc and Vms. The transition from one pattern to the other was located about in the middle of the small intestine. Tissue conductance decreased in both segments, probably due to a reduction of paracellular shunt conductance induced by the cell swelling. Voltage scanning experiments revealed that the observed decrease in total tissue conductance in the ileum was caused solely by a decrease in local conductance in the villus region while the crypt conductance did not change, suggesting that the decrease in paracellular conductance of the crypts is compensated by an increase in cellular conductance. The response in both segments was dependent on the presence of Cl- and was blocked by the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). It was not affected by the neurotoxin tetrodotoxin. In the jejunum the swelling-induced decrease in Isc was reduced in the presence of the cyclooxygenase inhibitor, indomethacin, or the lipoxygenase inhibitor, nordihydroguaiaretic acid. In the ileum the Cl- secretion induced by hypotonicity was blocked by the K+ channel blocker quinine and was reversed into a decrease in Isc when serosal Ca2+ was zero. We conclude that the observed volume regulatory changes are initiated in the jejunum by an eicosanoid-mediated opening of basolateral Cl- channels and in the ileum by a Ca2+-mediated opening of K+ channels which enhances apical Cl- efflux.

Activation of transcription factor NF-kappaB by the adenovirus E3/19K protein requires its ER retention

We have recently shown that the accumulation of diverse viral and cellular membrane proteins in the ER activates the higher eukaryotic transcription factor NF-kappaB. This defined a novel ER-nuclear signal transduction pathway, which is distinct from the previously described unfolded protein response (UPR). The well characterized UPR pathway is activated by the presence of un- or malfolded proteins in the ER. In contrast, the ER stress signal which activates the NF-kappaB pathway is not known. Here we used the adenovirus early region protein E3/19K as a model to investigate the nature of the NF-kappaB-activating signal emitted by the ER. E3/19K resides in the endoplasmic reticulum where it binds to MHC class I molecules, thereby preventing their transport to the cell surface. It is maintained in the ER by a retention signal sequence in its carboxy terminus, which causes the protein to be continuously retrieved to the ER from post-ER compartments. Mutation of this sequence allows E3/19K to reach the cell surface. We show here that expression of E3/19K potently activates a functional NF-kappaB transcription factor. The activated NF-kappaB complexes contained p50/p65 and p50/c-rel heterodimers. E3/19K interaction with MHC class I was not important for NF-kappaB activation since mutant proteins which no longer bind MHC molecules remained fully capable of inducing NF-kappaB. However, activation of both NF-kappaB DNA binding and kappaB-dependent transactivation relied on E3/19K ER retention: mutants, which were expressed on the cell surface, could no longer activate the transcription factor. This identifies the NF-kappaB-activating signal as the accumulation of proteins in the ER membrane, a condition we have termed "ER overload." We show that ER overload-mediated NF-kappaB activation but not TNF-stimulated NF-kappaB induction can be inhibited by the intracellular Ca2+ chelator TMB-8. Moreover, treatment of cells with two inhibitors of the ER-resident Ca(2+) -dependent ATPase, thapsigargin and cyclopiazonic acid, which causes a rapid release of Ca2+ from the ER, strongly activated NF-kappaB. We therefore propose that ER overload activates NF-kappaB by causing Ca2+ release from the ER. Because NF-kappaB plays a key role in mounting an immune response, ER overload caused by viral proteins may constitute a simple antiviral response with broad specificity.

Analysis of intra- and intercellular calcium signaling in a mouse malignant glioma cell line

Intra- and intercellular calcium signaling in glioma cells was examined by mechanical stimulation of a monolayer cell line of methylcholanthrene-induced mouse ependymoblastoma, 203-glioma, with a fine round-tip glass needle. A fura-2 fluorescence image of the glioma revealed a four- to eightfold increase in the cytosolic calcium ion concentration in directly stimulated signal cells. The increased calcium spread to surrounding cells at a speed of 20 microns/sec for a distance of up to 200 microns. Calcium was transmitted between adjacent cells and even in cells up to 200 microns distant from the initially stimulated cell. Microinjection of Lucifer yellow dye showed no gap junctional communication between cells. Depletion of extracellular calcium ion inhibited both cytosolic calcium elevation and propagation to neighboring cells by mechanical stimulus. An intracellular calcium blocker, TMB-8, eliminated the cytosolic calcium mobilization in a mechanically stimulated cell, but had no effect on calcium diffusion to surrounding cells. Nifedipine and verapamil, antagonists of voltage-dependent calcium channels, did not act on the mechanically induced calcium response. This suggests that some stimulating factor may trigger transmission of calcium, which may be ejected directly from single stimulated cells and mediated via a membrane receptor but not through a gap junction. The calcium signaling in a mechanically stimulated cell may be related to both an influx and a redistribution of intracellular calcium from internal stores, while calcium propagation to neighboring cells may involve calcium influx alone.

The effect of caffeine on prostaglandin output from the guinea-pig uterus

1. Caffeine increased the outputs of prostaglandin F2 alpha (PGF2 alpha), PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus on days 7 and 15 of the oestrous cycle. The effect on PGE2 output depended on the age of the animals and was absent in younger guinea-pigs (< 4 months). Theophylline also stimulated the outputs of PGF2 alpha and 6-keto-PGF1 alpha, but not the output of PGE2, from the day 7 guinea-pig uterus. 2. The stimulatory effects of caffeine on the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus were not prevented by lack of extracellular calcium, ryanodine or ruthenium red (both inhibitors of calcium release via the ryanodine receptor), although the increase in PGF2 alpha output tended to be slower when extracellular calcium was absent. Also, ryanodine flattened and broadened the peak of increased PGF2 alpha release. 3. The calmodulin antagonists, W-7 and trifluoperazine, had no inhibitory effect on the caffeine-stimulated increases in uterine prostaglandin output. In fact, W-7 (but not trifluoperazine) greatly potentiated the action of caffeine on uterine PGF2 alpha output, but had little or no potentiating effect on the action of caffeine on uterine PGE2 and 6-keto-PGF1 alpha outputs. 4. TMB-8, an intracellular calcium antagonist, inhibited the increase in PGF2 alpha output produced by caffeine without preventing the increases in outputs of PGE2 and 6-keto-PGF1 alpha. 5. These studies suggest that caffeine stimulates uterine PGF2 alpha synthesis and release by a mechanism dependent upon intracellular calcium, but this mechanism is not mediated by activation of any of the three well-characterized ryanodine receptors or by calmodulin. Furthermore, the increases in the synthesis and release of PGE2 and 6-keto-PGFI alpha. in the guinea-pig uterus induced by caffeine appear to involve mechanism(s) different from that which stimulates PGF2 alpha production.

Interferon-gamma increases cellular calcium ion concentration and inositol 1,4,5-trisphosphate formation in human renal carcinoma cells: relation to ICAM-1 antigen expression

In the present study, we investigated the effect of interferon-gamma (IFN-gamma) on cellular calcium ion concentration [Ca2+]i and inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) formation in the human renal carcinoma cell line CaKi-1. We also examined the possible role of a Ca(2+)-dependent mechanism during IFN-gamma-induced intercellular adhesion molecule 1 (ICAM-1) antigen expression. IFN-gamma caused a rapid concentration-dependent rise in [Ca2+]i, which was partly inhibited by diltiazem, a calcium channel blocker, TMB-8, an inhibitor of intracellular calcium redistribution, and in calcium-free medium. IFN-gamma caused a fourfold increase in Ins 1,4,5-P3 formation. The induction of ICAM-1 antigen expression was synergistically enhanced by 4-bromocalcium ionophore A23187. Finally, the calcium antagonists diltiazem. TMB-8 and EGTA, as well as two potent inhibitors of Ca(2+)-dependent kinases, calmidazolium (R24571) and W7, had no or only a minor inhibitory effect on IFN-gamma induction. Our data suggest that IFN-gamma increases [Ca2+]i in CaKi-1 cells by stimulating influx of Ca2+ and release of Ca2+ from intracellular stores, probably via Ins 1,4,5-P3 formation. IFN-gamma signal transduction in our model may not be limited to an increase in [Ca2+]i and Ins 1,4,5-P3, since IFN-gamma-induced ICAM-1 antigen expression was abrogated to a minor degree by calcium antagonists and not coupled to Ins 1,4,5-P3 formation.

Norepinephrine, unlike ATP, induces all-or-none increase in cytosolic calcium in thyroid cells. The role of inositol-trisphosphate-sensitive stores and calcium channels

The mechanism of action of norepinephrine and ATP has been analyzed in single FRTL5 cells (a normal thyroid cell line), loaded with the fluorescent Ca2+ probe Fura2. ATP increased the cytosolic Ca2+ in an apparently concentration-dependent manner with a maximal effect at 10 microM (413 +/- 26% over basal levels of 135 +/- 7 nM). In contrast, the norepinephrine-induced increase (198 +/- 5% over basal) was concentration independent in individual cells, the minimal effective concentration being 1 nM. However, the number of cells responding to norepinephrine was concentration dependent. The ATP-induced Ca2+ rise was biphasic, consisting of a rapid rise (2-4 s, 252 +/- 15%), resembling the effect of norepinephrine, followed by a slower and longer component, which reached a plateau in 0.5-2 min. The second component appeared to be related to the opening of a channel, since it required extracellular Ca2+ and was abolished by SC38249, an inhibitor of the second-messenger-operated and voltage-operated channels. Moreover, it was inhibited by 4 beta-phorbol 12-myristate 13-acetate, suggesting that protein kinase C might be involved in the modulation of this Ca2+ channel.

Cell transformation induces a cytoplasmic Ca2+ oscillator in Madin-Darby canine kidney cells

Alkaline stress transforms Madin-Darby canine kidney (MDCK) cells as indicated by loss of epithelial structure, multilayer cell growth and formation of foci. In the present study we report that transformed MDCK cells (MDCK-F cells) exhibit spontaneous and lasting oscillations of intracellular Ca2+ concentration ([Ca2+]i), which are absent in non-transformed cells. Oscillations, as revealed by Fura-2 video imaging, were due to the activity of an inositol 1,4,5-trisphosphate-(InsP3)-sensitive Ca2+ store since their frequency was dependent on bradykinin concentration and they were abolished by the phosphoinositidase C inhibitor U73122. Moreover, blockers of the cytoplasmic Ca(2+)-ATPase, thapsigargin and 2,5-di-(tetr-butyl)-1,4-benzohydroquinone inhibited oscillatory activity. In contrast, neither injection of ruthenium red, ryanodine nor caffeine had any effect on oscillations. Analysis of the spatial distribution of [Ca2+]i showed that Ca2+ transients originated from an initiation site constant for a given cell and spread through the cell as an advancing Ca2+ wave. Oscillations started in a random manner from single cells and spread over neighbouring cells, suggesting a kind of intercellular communication. We conclude that MDCK-F cells have acquired the ability for endogenous Ca2+ release through transformation. Oscillations are primarily due to the activity of an InsP3-sensitive cytosolic Ca2+ oscillator.

Rhythmic contractions of isolated small arteries from rat: role of calcium

In order to investigate the mechanisms behind rhythmic contractions in small arteries of the mesenteric arcade from Wistar rats, the calcium dependency of the oscillations in response to noradrenaline activation was tested on isolated vessels. Application of 1 microM ryanodine or 30 microM TMB-8 (procedures known to inhibit Ca2+ release from intracellular stores) totally abolished the rhythmic activity, even though the antagonists had opposite effects on the amplitude of the contractile response to noradrenaline. Verapamil (1 microM) or felodipine (1 nM) (agents known to inhibit influx of extracellular Ca2+) also abolished the oscillations and reduced the maximal noradrenaline response by about 40%. Reducing the extracellular Ca2+ concentration to 0.1 mM reduced the amplitude of the noradrenaline response to a similar extent as 1 nM felodipine, but did not eliminate the oscillations. This may indicate that the effect of calcium entry blockers was to eliminate the voltage-dependency of Ca2+ inflow rather than just reducing the Ca2+ level. Manoeuvres that would increase the cytosolic Ca2+ concentration (exposure to caffeine or to the calcium agonist BAY-K 8644) increased the frequency of the oscillations. These observations indicate an important role, not only for voltage-operating channels, but also for intracellular calcium stores in the generation of rhythmic contractions in these small arteries. Oscillations appear to be generated by an interplay between membrane activation and intracellular calcium stores.

Effect of TMB-8 on alpha-adrenoceptor agonist and KC1 induced-contractions in isolated rabbit aorta

1. TMB-8 (10(-6) M-10(-4) M) depresses the contractile effect of the selective alpha 1-adrenoceptor agonists methoxamine and phenylephrine in the isolated rabbit aorta. 2. TMB-8 also depresses contractions evoked by 80 mM KCl in this tissue when used at similar concentrations. 3. The calcium antagonist nifedipine potentiates the inhibitory effect of TMB-8 on the alpha 1-contractions. 4. In preparations mounted in Ca-free solution containing 0.5 mM EGTA, 10(-4) M TMB-8 markedly depressed the contractions caused by both alpha 1-adrenoceptor agonists. 5. The Ca2+ agonist BAY K 8644 (10(-6) M) partially prevented the inhibitory effect of TMB-8 on 80 mM KCl contractions.

Independent actions of asparagine and high levels of free Ca2+ in the induction of ornithine decarboxylase

During growth stimulation of cells, Ca2+ and amino acids of the A, ASC and N transport systems are important for the induction of ornithine decarboxylase (ODC, L-ornithine carboxylase, EC 4.1.1.17). In order to clarify the relationship between Ca2+ and amino acids, we studied the induction of ODC by asparagine under three different Ca2+ states in H-35 rat hepatoma cells. First, in normal cells, extracellular Ca2+ above 0.1 mM and 10 mM asparagine separately stimulated ODC activity and their effects were approximately additive. In these normal cells, asparagine could act in the absence of medium Ca2+. TMB-8, a sequestered-Ca2+ release antagonist, had no effect on ODC induction whilst the asparagine action is sensitive to treatment with W7, a Ca-calmodulin antagonist, or lanthanum, a Ca2+ antagonist. Secondly, in cells treated with 0.5 mM EGTA in Ca(2+)-free medium, the asparagine action on ODC induction was blocked but the inhibition could be reversed by the addition of Ca2+ to the medium. Thirdly, ionomycin treatment in the absence of medium Ca2+ did not block the asparagine effect. Furthermore, in ionomycin-treated cells, the presence of high levels of medium Ca2+ increased ODC activity, but this increase was additive to, and could not replace, the action of asparagine. Our results indicate that the asparagine action does not depend on an increase of intracellular free-Ca2+.

The effects of platelet-activating factor on the output of prostaglandins from the guinea-pig uterus

Platelet-activating factor (PAF) significantly increased the output of prostaglandin (PG) F2 alpha from the guinea-pig uterus during the mid-cycle phase (Days 6-10), but only had a small, non-significant stimulatory effect on the outputs of PGE2 and 6-keto-PGF1 alpha. PAF significantly increased the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus during the later phase of the cycle (Days 15-17). Lack of extracellular calcium did not affect the stimulatory effect of PAF on uterine PG output. However, TMB-8 (an intracellular calcium antagonist) prevented the increases in uterine PG output produced by PAF at both phases of the cycle. These results suggest that the stimulatory effect of PAF on uterine PG output in the guinea-pig is dependent upon the mobilization of intracellular calcium but is not dependent upon the uptake of extracellular calcium. Also, the weak stimulatory effect of PAF on PGE2 output from the uterus during the mid-cycle phase indicates that, if PAF is involved in implantation in guinea-pigs, it probably does not act via PGE2. Also, the lack of an inhibitory effect of PAF on uterine PGF2 alpha synthesis and release suggests that PAF is not the anti-luteolytic factor produced by the guinea-pig conceptus during early pregnancy.

Calcium-dependent prostaglandin biosynthesis by lipopolysaccharide-stimulated rat Kupffer cells

Isolated rat Kupffer cells produced and released prostaglandin (PG) E2, 6-keto-PGF1 alpha, and thromboxane B2 (TXB2) in response to lipopolysaccharide (LPS) stimulation. This elevation of PGE2, 6-keto-PGF1 alpha and TXB2 in the medium was not observed when cells were cultured in the absence of extracellular calcium or in the presence of an extracellular calcium chelator, EGTA. An intracellular calcium antagonist, TMB-8, also suppressed the production of PGE2, 6-keto-PGF1 alpha and TXB2 in a concentration-dependent manner. The intra-cellular calcium concentration of Kupffer cells elevated early after the addition of LPS determined by the use of fura-2 and a fluorescence microscopy. Moreover, calmodulin inhibitors, W-7 and W-13, apparently inhibited the production of PGF2, 6-keto-PGF1 alpha and TXB2. All these results suggest that LPS-induced PG production by stimulated rat Kupffer cells may be regulated by a calcium-calmodulin pathway.

Activation of basolateral Cl- channels in the rat colonic epithelium during regulatory volume decrease

Exposure to a hypotonic medium caused an increase in the diameter of isolated crypts from the rat colon. The increase in cell volume was only transient and lasted about 7 min. Despite of the continuous presence of the hypotonic medium, cell volume decreased again. This regulatory volume decrease (RVD) was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), a Cl- channel blocker, and by Ba2+, a K+ channel blocker. Cell-attached patch-clamp recordings revealed that the RVD was associated with the activation of previously silent basolateral channels. These channels were identified after excision of the patch as Cl- channels (28 pS) and as K+ channels (45-60 pS). The RVD was dependent on the presence of external Ca2+. The phospholipase A2 inhibitor, quinacrine, and the lipoxygenase blocker, nordihydroguaiaretic acid, inhibited RVD, while indomethacin had no effect. In Ussing chamber experiments an exposure to hypotonic media caused an initial, transient increase in tissue conductance (Gt), followed by a prolonged decrease in short-circuit current (Isc) and the potential difference (V). The height of the electrical response was dependent on the decrease in the osmolarity in a range from 20 mosmol l-1 to 90 mosmol l-1. The increase in Gt was blocked by NPPB and Ba2+, whereas the decrease in Isc or V was inhibited by NPPB but enhanced by Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

Effects of 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB8) on rat atrial muscle

Rat atria loaded in vitro with the dye INDO-1 produced fluorescence signals indicative of changes in cytoplasmic calcium ion concentration ([Ca2+]c). Such atria showed systolic/diastolic fluctuations in fluorescence indicative of a systolic rise and a diastolic fall in [Ca2+] while being superfused with a solution containing a normal Ca2+ concentration. Some atria were then exposed to a low [Ca2+] in the superfusate. This caused negative inotropism and fluorescence changes indicative of a decline in [Ca2+]c. Both of these responses were reversed by adding 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB8; 2 microM) to the superfusate. Some atria were exposed instead either to a low [K+] in the superfusate or to an ouabain-containing superfusate. These atria developed a contracture, associated with fluorescence changes indicative of a rise in [Ca2+]c. The addition of TMB8 (2 microM) now relaxed the contracture, and this was associated with fluorescence changes indicative of a decline in [Ca2+]c. Atria that were exposed for 15 min to a low [Na+] in the superfusate developed a period of positive inotropism, followed by a brief period of negative inotropism on return to the normal superfusate. The period of positive inotropism was associated with fluorescence changes indicative of a rise in [Ca2+]c and the period of negative inotropism with a decline in [Ca2+]c to below baseline levels. All of these responses were less marked in atria exposed throughout to superfusates containing TMB8 (2 microM). Some atria were loaded with the dye SNARF-1. This emits fluorescence signals indicative of changes in cytoplasmic pH (pHc). These atria showed no systolic/diastolic fluctuation of fluorescence, but when superfused with a bicarbonate-free solution they displayed a change in fluorescence indicative of a decline in pHc in response to the addition of either ouabain or TMB8. Similarities were found between the effects produced by TMB8 and those produced by amiloride or dichlorobenzyl amiloride, suggesting that all three agents inhibit plasmalemmal Na+/Ca2+ and Na+/H+ exchange.

Effects of inhibitors and ion substitutions on oscillations of cell membrane potential in cells expressing the RAS oncogene

Previous studies revealed that in NIH fibroblasts expressing the ras oncogene but not in other NIH fibroblasts, bradykinin leads to sustained, calcium dependent oscillations of cell membrane potential by repetitive activation of calcium-sensitive K+ channels. The present study has been performed to test for ion and inhibitor sensitivity of these oscillations. Both, Lys-bradykinin (kallidin) and bradykinin, but not any shorter peptide tested, maintained the oscillations. The oscillations are abolished in the presence of the K+ channel blocker barium (10 mmol/l). The amplitude but not the frequency of the oscillations is dependent on the extracellular potassium concentration. The oscillations are not dependent on the presence of extracellular sodium, bicarbonate or chloride. The oscillations are abolished in the absence of extracellular calcium and their frequency is significantly decreased at reduced extracellular calcium (to 0.2 mmol/l). The oscillations are not inhibited by acute administration of ouabain (0.1 mmol/l), by dimethylamiloride (100 mumol/l), furosemide (1 mmol/l) and hydrochlorothiazide (100 mumol/l), by cobalt (100 mumol/l), zinc (100 mumol/l), gadolinium (100 mumol/l), verapamil (10 mumol/l) and diltiazem (10 mumol/l), but are abolished in the presence of 100 mumol/l lanthanum, 1 mmol/l cadmium, 10 mumol/l nifedipine, 25 mumol/l SK & F 96365 and 200 mumol/l TMB-8. Stimulation of calcium entry by 10 nmol/l ionomycin is frequently followed by oscillations of cell membrane potential even in the absence of bradykinin. In conclusion, in cells expressing the ras oncogene bradykinin leads to sustained activation of calcium channels at the cell membrane, which cause oscillations of the cell membrane potential by triggering intracellular calcium release.

Effect of Ca2+ modulators on acetylcholine-induced phasic and tonic contractions and A23187-induced contractions in ileal longitudinal muscle and IP3 production

The influence of different sources of Ca2+ on the Emax and ED50 values of acetylcholine (ACh)-induced phasic and tonic contractions and on A23187-induced contractions was studied using different extracellular Ca2+ concentrations ([Ca2+]o) and the Ca2+ modulators TMB-8 and D600. IP3 production induced by both stimulants was also studied. The results are compatible with: (a) the mobilization of Ca2+ from an intracellular source as a primary event in the phasic response. (b) The primary involvement of a D600-sensitive inward Ca2+ current in the ACh-tonic response. (c) An inward D600-sensitive Ca2+ current associated with the ionophore transported ion. (d) The involvement of an IP3 independent, TMB-8 sensitive mechanism of Ca2+ mobilization involved in the A23187-induced responses.

In vitro effects of PAF on venous endothelial cell actin disposition

Venous endothelial cells have been stained in vitro for the contractile protein actin, using an immunofluorescence technique. Semi-automated image analysis showed that treatment with platelet-activating factor (PAF 5 x 10(-7) M) caused elongation of endothelial cells and alteration in their actin-staining characteristics. These changes are prevented by the PAF antagonist BN52021 (1 x 10(-5) M and 1 x 10(-6) M) and the absence of extracellular Ca++. It is suggested that it is the resultant decrease in intracellular Ca++ levels which is responsible for preventing the effects of PAF.

Na+/K+/Cl- cotransport is stimulated by a Ca(++)-calmodulin-mediated pathway in BALB/c 3T3 fibroblasts

In the present study, we investigated the role of intracellular Ca++ in the stimulation of the Na+/K+/Cl- cotransport in synchronized BALB/c 3T3 cells. The Na+/K+/Cl- cotransport was stimulated by the growth factors EGF, TGF-alpha, IGF-1, and IGF-2, which do not activate protein kinase C, but do induce a transient increase in free cytoplasmic Ca++. In addition, direct activation of protein kinase C by the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) did not affect the Na+/K+/Cl- cotransport activity of quiescent cells. The Na+/K+/Cl- cotransport was also stimulated by the above mitogens in cells pretreated with the phorbol ester TPA. This treatment led to a progressive decline in the activity of cellular protein kinase C. This result implies that cells deficient in protein kinase C may still support stimulation of the Na+/K+/Cl- cotransport. Taken as a whole, these findings suggest that the Na+/K+/Cl- cotransport is stimulated predominantly by a protein kinase C-independent mechanism in BALB/c 3T3 fibroblasts. Both the intracellular Ca++ antagonist 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) and two potent calmodulin antagonists, trifluoperazine (TFP) and chloropromazine (CP), blocked serum- and mitogen-stimulated Na+/K+/Cl- cotransport. These results suggest that the Na+/K+/Cl- cotransport is stimulated by an increase of intracellular Ca++ and subsequently by a Ca(++)-calmodulin-mediated pathway in the synchronized BALB/c 3T3 fibroblasts.

Extracellular Na+ dependency of free cytosolic Ca2+ regulation in aortic vascular smooth muscle cells

This study examined contribution of Na(+)-dependent processes to the regulation of free cytosolic calcium (Ca2+i) in cultured vascular smooth muscle cells (VSMC) using fura-2. Removal of Na+ from superfusate (replacement with choline) resulted in an increment of Ca2+i that was greatly augmented by pretreatment with ouabain. Under both conditions, Ca2+i increase was followed by partial recovery to a new steady state that was still significantly higher than that seen before removal of external Na+ (Na+o). In ouabain-pretreated cells lowering of Na+o caused progressive increases in Ca2+i. Addition of NiCl2, a Na(+)-Ca2+ exchange inhibitor, completely blocked the increase in Ca2+i produced by removal of Na+o, indicating that the Na(+)-Ca2+ antiporter was responsible for observed Ca2+i changes. Ca2+i increase produced by reduction of Na+o was also seen after depletion of inositol trisphosphate-sensitive Ca2+ stores with repeated pulses of angiotensin II or after blockade of sarcoplasmatic reticulum Ca2+ release with TMB-8 but was not observed in the absence of external Ca2+. These observations indicate that the source of Ca2+i increase in response to changes in the transmembrane Na+ gradient is largely external, and potentiation of the Ca2+i surge by ouabain suggests Ca2+ influx via the Na(+)-Ca2+ exchanger operating in the reverse mode. The relative contribution of a Na(+)-dependent and -independent component of Ca2+i recovery was investigated by superfusing cells with ionomycin in a Na(+)-free medium and later adding Na+ to the medium. This Ca2+ ionophore increased Ca2+i to a peak, and this was followed by a rapid but partial recovery to a new steady state. Readdition of varying amounts of Na+ to the superfusate, in the continued presence of ionomycin, resulted in concentration-related decline in Ca2+i, thereby uncovering a substantial contribution of a Na(+)-dependent mechanism of Ca2+i regulation. Decline of Ca2+i produced by readdition of Na+ was blocked by addition of NiCl2 to the superfusate. Our findings thereby provide evidence for Ca2+i regulation in VSMC via a Na(+)-dependent mechanism, consistent with a Na(+)-Ca2+ exchanger, which acts as a Ca2+ efflux mechanism when Ca2+i is elevated. Na(+)-Ca2+ exchanger acts as a Ca2+ influx mechanism when intracellular Na+ is elevated by prior exposure to ouabain.

Segment-specific effects of the heat-stable enterotoxin of E. coli on electrolyte transport in the rat colon

The heat-stable enterotoxin of E. coli (STa) induced an increase in short-circuit current (Isc) in the rat colon. The maximal increase in Isc was about three times larger in the proximal than the distal colon. The action of STa was mimicked by 8-Br-cyclic GMP. Unidirectional flux measurements revealed that STa decreased Na+ and Cl- absorption in the distal colon, while it decreased Na+ absorption and activated Cl- secretion in the proximal colon. In the distal, but not in the proximal colon, indomethacin inhibited the action of STa and of 8-Br-cyclic GMP. Inhibition by indomethacin could be overcome by addition of prostaglandin E2 or forskolin, but not by addition of a non-hydrolysable analogue of cyclic AMP, suggesting an action of STa on cyclic AMP hydrolysis. Amrinone and trequinsin, two inhibitors of cyclic GMP-inhibited phosphodiesterases, mimicked the action of STa on Isc and inhibited the response to a subsequent administration of the toxin indicating the modulation of a cyclic GMP-inhibited phosphodiesterase by STa in the distal colon. The results give evidence for different intracellular action sites of STa in the two parts of the rat colon.

TMB-8 prevents the hydroosmotic response to ADH in rabbit cortical collecting tubules

Both AVP and dDAVP effect a transient increase in cytosolic free calcium (iCa2+) in cortical collecting tubule (CCT) cells. To investigate the physiological role of this increase in iCa2+, we examined the effect of TMB-8, a putative inhibitor of iCa2+ release, on the initial and sustained phase of AVP- and dDAVP-stimulated water permeability (Pf) in isolated, perfused CCTs. Pretreatment of tubules with TMB-8, 50 microM, suppressed the increase in osmotic water permeability (Pf) induced by 10 microU/ml AVP and dDAVP, but had no effect on the sustained phase of the response. When increased to 100 microM. TMB-8 inhibited the sustained phase of AVP action. A similar pattern was observed on AVP-stimulated adenyly cyclase activity in rabbit renal membranes. Pretreatment of tubules with 50 microM TMB-8 attenuated the initial increase in Pf in response to cholera toxin but not to 8-Br-cAMP or forskolin. There was no effect of this concentration of TMB-8 on the sustained phase of these agonists. These studies suggest that, in lower concentrations, TMB-8 inhibits the mobilization of iCa2+, which is important for the interaction of Gs with the catalytic unit of adenylyl cyclase and the initial increase in AVP-stimulated Pf. In higher concentrations, TMB-8 inhibits adenylyl cyclase activity directly.