On the salt-linkage formations of porous and nonporous silica particles with trimethylammonium glycol chitosan iodide

The stoichiometry of the salt-linkage formations of nonporous and porous silica particles with trimethylammonium glycol chitosan iodide (TGCI) was investigated by comparing the results of colloid titration and adsorption experiments with those of potentiometric titrations. The surface charge (Q) of colloidal silica as function of pH was evaluated by means of the colloid titration with TGCI. On the other hand, the density (D) of ≡ SiO^? groups of silica gel at different pH was also evaluated by the adsorption experiment of TGCI. These results obtained were compared with the Q vs. pH and D vs. pH curves which were obtained by the potentiometric titrations at various ionic strengths for colloidal silica and silica gel, respectively. It was concluded that the ≡ SiO^? groups on the surface of nonporous colloid silica form the salt-linkages stoichiometrically with ^⊕N(CH₃)₃-groups in TGCI, whereas the salt-linkage formation between ^⊕N(CH₃)₃-groups in TGCI and ≡ SiO^? groups of silica gel does not follow the stoichiometric relationship, since the salt-linkages of the ≡ SiO^ominus; groups in the pores of the silica gel could be affected by the steric hindrance of the TGCI chain.     

Iodine-poly(vinyl alcohol) interactions, 5. Releasing mechanism of I− and I2 in the decomposition process of the blue complex

By treating a blue-colored solution of poly(vinyl alcohol) (PVA), iodine and boric acid with an anion exchange resin, a solution consisting only of the polyiodide ion bound to the PVA matrix was obtained. In order to re-establish the equilibrium between polyidodide, I₂ and I^?, the bound polyiodide ions decomposed to I^? and I₂. When this happend at temperatures below 10°C, only I^? was released from the PVA matrix with I₂ remaining in it, and a new equilibrium state was reestablished. However, above 20°C all polyiodide ions were decomposed without recovering the equilibrium of the reaction. In this case both I₂ and I^? were released from the PVA matrix. Based on these findings a new mechanism for the formation and decomposition of polyiodide ions was deduced. From the initial and equilibrium concentrations of the polyiodide ions at 5 and 10°C, approximate dissociation constants to I^? (free) and I₂ (bound) were estimated.     

The relationship between the membrane potential of neurosecretory nerve endings,as measured by a voltage-sensitive dye,and the release of neurohypophysial hormones

The membrane potential of isolated rat neurohypophyses and isolated neurosecretosomes (neurosecretory nerve endings) was monitored with the voltage sensitive fluorescent probe diS-C₃-(5). K ions, in contrast to Na or Cl ions, give rise to large changes of the fluorescent signal. The fluorescent response is linearly related to log[K⁺]₀ at values higher than 10 mM, whereas at lower [K⁺]₀ the permeability of the membrane for Na ions has to be taken into account. Veratridine increases the fluorescent signal only in the presence of external sodium; this effect is blocked by tetrodotoxin. After prolonged K-induced depolarisation, addition of veratridine to the medium gives a further change in fluorescence of diS-C₃-(5) associated with release of vasopressin.Vasopressin release from isolated neurohypophyses started to increase significantly only above 25 mk [K⁺]₀, while the depolarization of the membrane was linearly related to log[K⁺]₀. The results are consistent with the view that neurosecretory nerve endings have voltage-dependent calcium channels that regulate the amount of hormone released during depolarisation.     

Iodine-poly(vinyl alcohol) interactions, 4. Stoichiometry of iodine/iodide in the polyiodide ion bound in the cage of poly(vinyl alcohol)

Aqueous poly(vinyl alcohol) (PVA)-iodine-boric acid solution was treated with anion exchange resin and the system involving only the cage complex was isolated. The system was then extracted with carbon tetrachloride, and I₂ and I^?, which were released from the complex, were separated and pooled in the carbon tetrachloride and the aqueous layers, respectively. From the absorption spectra of the layers the amounts of I₂ and I^? were determined. The ratio I₂/I^? was found to be approximately 2,0, which corresponds to the I₂/I^? stoichiometry in the complex. This result suggested that the major species bound in the PVA cage are pentaiodide ions, i.e., I with linear configuration and/or I₂· I with distorted chain structure. Judging from the resonance Raman spectrum of the PVA-iodine solution that had been revealed before, it was concluded that the two absorption bands of the complex at λ_max = 650 and 355 nm are ascribed to the I and I₂ · I ions, respectively.     

Controlled release of strontium ions from a bioactive Ti metal with a Ca-enriched surface layer

A nanostructured sodium hydrogen titanate layer ∼1 μm in thickness was initially produced on the surface of titanium metal (Ti) by soaking in NaOH solution. When the metal was subsequently soaked in a mixed solution of CaCl₂ and SrCl₂, its Na ions were replaced with Ca and Sr ions in an Sr/Ca ratio in the range 0.18–1.62. The metal was then heat-treated at 600 °C to form strontium-containing calcium titanate (SrCT) and rutile on its surface. The treated metal did not form apatite in a simulated body fluid (SBF) even after 7 days. When the metal formed with SrCT was subsequently soaked in water at 80 °C, the treated metal formed bone-like apatite on its surface within 1 day in SBF since the Ca ions were partially replaced with H₃O⁺ ions. However, it released only 0.06 ppm of Sr ions even after 7 days in phosphate-buffered saline. When the metal was soaked after the heat treatment in 1 M SrCl₂ solution instead of water, the treated metal released 0.92 ppm of Sr ions within 7 days while maintaining its apatite-forming ability. The Ti formed with this kind of bioactive SrCT layer on its surface is expected to be highly useful for orthopedic and dental implants, since it should be able to promote bone growth by releasing Sr ions and tightly bond to the bone through the apatite formed on its surface.     

Propene polymerization on titanium-magnesium catalysts, 4. ESR study of TI3+ ions

The role of Ti³⁺ ions in titanium-magnesium catalysts of various composition, TiCl₄/MgCl₂ + AlR₃, TiCl₄/MgCl₂ + Al(i-Bu)₃ + EB, TiCl₄/EB/MgCl₂ + Al(i-Bu)₃ and TiCl₄/EB/MgCl₂ + Al(i-Bu)₃ + EB, was studied by means of ESR. The ESR data and the catalytic properties were compared. It could be shown that the introduction of ethyl benzoate (EB) leads to an increase of stereospecificity, to a considerable increase of the portion of Ti³⁺ ions which can be observed by ESR, to the appearance of several new signals in the ESR spectra and to an increase of the portion of titanium in solution, removed from the solid catalyst during the interaction with the organoaluminium cocatalyst. Titanium ions are found mainly in the particles or surface associates whose Ti³⁺ ions produce no signals in the ESR spectra, Ti³⁺ ions observed by ESR are found to be inactive centers of polymerization. The active centers appear to be localized in highly dispersed particles or surface associates of TiCl₃, formed on the MgCl₂ surface and are not revealed in the ESR spectra. Increasing stereospecificity in the presence of EB is assumed to be caused by deactivation of non-stereospecific active centers with ethyl benzoate.     

Activation of a slow outward current by the calcium released during contraction of cultured rat skeletal muscle cells

A slow outward current, activated during depolarization, which induced contraction in whole-cell patch-clamped rat skeletal muscle cells in primary culture [10], was extensively characterized in the present study. This current, I _O, was simultaneously recorded with the contraction as a slow outward current during the test pulse, and a slow outward bell-shaped tail after repolarization. I _O never appeared below the threshold potential for contraction, and the tail amplitude displayed a similar evolution with peak contraction amplitude as a function of membrane potential. This feature is consistent with the fact that I _O was suppressed when contraction was blocked by 5 M nifedipine [10], and it suggests that I _O was dependent on calcium released during contraction. This was confirmed by the fact that the presence of 10 mM EGTA in the patch pipette prevented the development of both contraction and I _O, and that I _O could be activated during caffeine-induced contractures without applying depolarizations. I _O could be carried by K⁺ or Cs⁺ ions, but not by Na⁺. The pharmacology of I _O was different from that of Ca²⁺-dependent BK and SK channels, since it was resistant to tetraethylammonium (135 mM), charybdotoxin (25 nM) and apamin (50 nM). I _o was also insensitive to 4-aminopyridine (1 mM) but blocked by 5 mM Ba²⁺ without change to contraction. It was concluded that rat cultured myoballs exhibit a Cs⁺ permeation through an atypical K⁺ channel type, which is activated by the calcium released during contraction.     

Multifunctional mesoporous nanoparticles as pH-responsive Fe reservoirs and artemisinin vehicles for synergistic inhibition of tumor growth

Artemisinin (ART) is an iron-dependent anti-cancer drug. However, simultaneous delivery of hydrophobic ART and Fe²⁺ ions into cancer cells remains a major challenge. Herein, we reported Fe₃O₄@C/Ag@mSiO₂ (FCA@mSiO₂) multifunctional nanocarriers which can load ART as high as 484 mg/g. Moreover, FCA@mSiO₂ nanoparticles demonstrated pH-responsive Fe²⁺ release, the concentration of Fe²⁺ ions can reach 2.765 nmol/L in HeLa cells cultured with FCA@mSiO₂ nanoparticles. The antitumor efficacy of ART-loaded FCA@mSiO₂ nanoparticles measured by MTT assay was significantly enhanced compared with free ART. It was suggested that the ART-loaded FCA@mSiO₂ nanoparticles are internalized by HeLa cells and located at the acidic compartments of endosomes and lysosomes, releasing Fe²⁺ ions to non-enzymatically convert ART to toxic products for killing cancer cells. This result provides a way for using promising natural drugs in anti-cancer therapeutics.     

A New Method for Preventing Catalytic Degradation of Cotton Cellulose by Ferrous or Ferric Ions During Bleaching with Hydrogen Peroxide

Tendering of cotton cellulose caused by the presence of Fe²⁺ and/or Fe³⁺ ions during bleaching with H₂O₂ using the exhaustion method and the pad‐steam method were studied. This was carried out by staining the cotton fabric samples with different concentrations of Fe²⁺ or Fe³⁺ ions then subjecting these samples to bleaching. Ceasing of cotton tendering resulting from Fe²⁺ and/or Fe³⁺ during bleaching with H₂O₂ by pretreatment of the fabric by oxalic acid were also studied under a variety of conditions. The onset of this pretreatment on the properties of the cotton fabric compared to the untreated fabric are discussed. The samples were monitored for degree of polymerization, Eisenhut's tendering factor, whiteness index, tensile strength and elongation at break. Results obtained show that the catalytic degradation of the cotton samples resulting from Fe²⁺ and Fe³⁺ ions are identical and the maximum tendering was observed when the fabric samples were contaminated with 0.3 mg/g fabric Fe²⁺ and/or Fe³⁺ ions. The catalytic degradation is much higher when the cotton samples were bleached with the pad‐steam than with the exhaustion method. The ceasing of such catalytic tendering could be achieved by pretreatment of the cotton fabrics with a bath containing 1% oxalic acid at 40°C for 1 min. The pretreated fabrics have higher degree of polymerization, whiteness index, tensile strength and lower Eisenhut's tendering factor compared with the untreated fabrics. The state of the fabric (i. e., grey, desized, scoured) does not play any significant role in such pretreatment.     

Study on Metal Ion Adsorption of Bifunctional Chelating/Ion‐Exchange Resins

Ion‐exchange resin has been considered as a suitable material for the recovery of heavy metals in water treatment. The chelating group, iminodiacetic acid (—R—N(CH₂COOH)₂), was introduced into the weak‐acid type (—R(COOH)—)_n—) ion‐exchange resin to obtain bifunctional ion‐exchange resins. Chromic, cupric, cadmium and lead ions were employed for adsorption experiments in this study. In isothermal experiments, the order of heavy metal ion adsorption decreased with increasing diameter of the heavy metal ion when the chelating group content was less than half. On the contrary, the adsorbed amount of lead ion would be higher than that of cadmic ion as the quantity of chelating group content was more than half owing to the stability constant difference (K_s[Pb2+] = 10^17.5 > K_s[Cd2+] = 10^5.71 in iminodiacetic acid). The adsorption efficiency of bifunctional ion‐exchange resins, especially for lead ions, would increase with rising chelating group content (from 0.08 mmol/mmol COOH to 0.31 mmol/mmol COOH). Meanwhile, the working pH range for metal ion adsorption in bifunctional ion‐exchange resins was extended from 2.5 down to 0.5. Addition of chelating groups to weak acid ion‐exchange resins could increase the adsorption efficiency for metal ions owing to the increased free volume of polymer structure.     

Virulence modulation of Candida albicans biofilms by metal ions commonly released from orthodontic devices

The installation of metal devices leads to an increase in the salivary concentration of metal ions and in the growth of salivary Candida spp. However, the relationship between released metal ions and Candida virulence has not been previously examined. The objective of this study was to evaluate whether metal ions affect fungal virulence. We prepared culture media containing Ni²⁺, Fe³⁺, Cr³⁺, Co²⁺ or a mixture of these metal ions at concentrations similar to those released in saliva of orthodontic patients. Biofilms of Candida albicans SC5314 were grown for 72 h and their biomasses were determined. The supernatants were analyzed for secretory aspartyl protease (SAP) and hemolysin activities. To verify changes in virulence following treatment with metals, proteolytic and hemolytic activities were converted into specific activities. The results revealed that all ions, except Co²⁺, caused increases in biofilm biomass. In addition, Ni²⁺ caused an increase in SAP activity and Fe³⁺ reduced hemolytic activity. However, the SAP and hemolysin activities in the presence of the mixture of ions did not differ from those of control. These results indicate that metal ions released during the degradation of orthodontic appliances can modulate virulence factors in C. albicans biofilms.     

Intracellular Mg2+ inhibits the IP3-activated I K(Ca) in NG108-15 cells. [Why intracellular citrate can be useful for recording I K(Ca)]

Receptor-mediated formation of inositol 1,4,5-trisphosphate (IP₃) can induce an outward Ca²⁺-activated K⁺ current [I _K(Ca)] some neural cells. We have investigated I _K(Ca) activated by intracellular injections of IP₃ in whole-cell patch-clamped neuroblastoma×glioma hybrid cells. The current could only be recorded reliably using citrate as the anion in the pipette, but not using acetate, aspartate, chloride, fluoride, gluconate or methylsulphate. This could be attributed to buffering of intracellular Mg²⁺ by citrate. Theoretical calculations suggested free [Mg²⁺] of 1.0 and 0.07 mM respectively in the acetate- and citrate-based recording solutions. Further, IP₃-activated I _K(Ca) could be recorded when the free Mg²⁺ level in the acetate, chloride or methylsulphate solutions was lowered to the range (0.05 mM) calculated for the citrate solution. Thus, raised [Mg²⁺] blocks I _K(Ca). This appeared to be due to inhibition of the response to released Ca²⁺, since high [Mg²⁺] also blocked the response to intracellular injections of Ca²⁺ ions. Mean Mg²⁺ levels in intact neuroblastoma×glioma hybrid cells measured by Mag-Indo-1/AM fluorescence were estimated to be less than 0.14 mM. We therefore conclude that IP₃-induced I _K(Ca) is expressed under normal conditions, but may be subject to regulation by intracellular Mg²⁺.     

Study of the state of titanium ions and the composition of the active component in titanium-magnesium catalysts for ethylene polymerization

The state of Ti³⁺ ions formed at various steps of preparation and activation of highly active titanium-magnesium catalysts of various composition (dry milling of TiCl₃ with MgCl₂; reduction of TiCl₄ by nonsolvated magnesium dialkyl; interaction of the TiCl₄/MgCl₂ system with an organoaluminium compound) was studied by the ESR method. It was found that in all systems studied the same three types of Ti³⁺ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCl₂. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti³⁺ ions formed in all systems enter the composition of particles or surface aggregates of TiCl₃ and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium-magnesium catalysts are supposed to be constituents of these particles or of surface aggregates.     

The cytotoxicity of cadmium-based quantum dots

Semiconductor Quantum dots (QDs) have raised great attention because of their superior optical properties and wide utilization in biological and biomedical studies. More recently, there have been intense concerns on cytotoxicity assessment of QDs. Most QDs are made of heavy metal ions (e.g., Cd²⁺), which may result in potential in vitro toxicity that hampers their practical applications. In this article, we aim to summarize recent progress on mechanistic studies of cytotoxicity of II-IV QDs. We have studied the cytotoxicity of a series of aqueous synthesized QDs (aqQDs), i.e. CdTe, CdTe/CdS core-shell structured and CdTe/CdS/ZnS core-shell-shell structured aqQDs. Our results suggested that released cadmium ions are responsible for the observed cytotoxicity of cadmium-based QDs. The fact that CdTe/CdS/ZnS core-shell-shell structured QDs are nearly nontoxic to cells further confirmed the role of released cadmium ions on cytotoxicity, and the effective protection of the ZnS shell. However, intracellular level of Cd²⁺ ions cannot be the only reason since the comparison with CdCl₂-treated cells suggests there are other factors contributed to the cytotoxicity of aqQDs. Our studies on genome-wide gene expression profiling and subcellular localization of aqQDs with synchrotron-based scanning transmission X-ray microscopy (STXM) further suggest that the cytotoxicity of CdTe QDs not only comes from the release of Cd²⁺ ions but also intracellular distribution of QD nanoparticles in cells and the associated nanoscale effects.     

In vitro studies on a two-pool storage of adrenaline and noradrenaline in granule material from bovine adrenal medulla

Adrenal medullary granules were isolated by millipore filtration according to Poisner & Trifaró (1967) and then lysed in deionized water. In a perfusion system the influence of concentration and pH was studied on the uptake of biogenic amines (PhEA, TA, DA, NA, A, Ach and Hi) and sodium ions by lysed and by dialyzed material. The results suggest a two-pool storage of A and NA in the granules. A minor pool with cation exchanger properties binds unselectively organic (biogenic amines) and inorganic cations with a U_max of 400–500 nmol/mg granules dry-weight. This minor pool (pool 1) was fully charged at amine concentrations >10 mM. A larger pool binds selectively A and NA-possibly stereospecifically L-NA and L-A—with a U_max?1500 nmol/mg granules. This larger pool (pool 2) required A and NA concentrations ?200–300 mM for maximal filling. In pool 2 CA⁺ ions are assumed to be electrostatically linked to carboxyl groups, which become available as hypothetical COO^-—⁺H₃N salt bridges are successively forced open by increasing CA concentrations (>10–30 mM). ATP^- ions become attached to the concomitantly unmasked ⁺NH₃ groups.     

Imipramine enhances cell proliferation and decreases neurodegeneration in the hippocampus after transient global cerebral ischemia in rats

This study was aimed to determine whether imipramine chronic treatment promotes neurogenesis in the dentate gyrus (DG) and interferes with neuronal death in the CA1 subfield of the hippocampus after transient global cerebral ischemia (TGCI) in rats. After TGCI, animals were treated with imipramine (20 mg/kg, i.p.) or saline during 14 days. 5-Bromo-2′-deoxyuridine-5′-monophosphate (BrdU) was injected 24 h after the last imipramine or saline injection to label proliferating cells. In order to confirm the effect of TGCI on neuronal death and cell proliferation, a group of animals was sacrificed 7 days after TGCI. Neurogenesis and neurodegeneration were evaluated by doublecortin (DCX)-immunohistochemistry and Fluoro-Jade C (FJC)-staining, respectively. The rate of cell proliferation increases 7 days but returns to basal levels 14 days after TGCI. There was a significant increase in the number of FJC-positive neurons in the CA1 of animals 7 and 14 days after TGCI. Chronic imipramine treatment increased cell proliferation in the SGZ of DG and reduced the neurodegeneration in the CA1 of the hippocampus 14 days after TGCI. Immunohistochemistry for DCX detected an increased number of newly generated neurons in the hippocampal DG 14 days after TGCI, which was not affected by imipramine treatment. Further studies are needed to evaluate whether imipramine treatment for longer time would be able to promote survival of newly generated neurons as well as to improve functional recovery after TGCI.     

Ionophore A23187 can mimick the changes in membrane permeability that occur during acetylcholine-stimulation of pancreatic acinar secretion

Acetylcholine (ACh) released from vagal terminals increases the permeability of the pancreatic acinar membrane to Na⁺ and Ca²⁺ ions. In this report, we compare the induced changes in intracellular Na⁺ and Ca²⁺ electrode potentials (E_Na and E_Ca) due to ACh-stimulation of acini with those observed during stimulation with the calcium ionophore, A23187, which mimicks the action of ACh on pancreatic secretion. Stimulation with ACh concentrations varying from 10^–8 to 10^–5 M and with A23187 concentrations of 10^–6 and 10^–5 M caused parallel increases in cytosolic Ca²⁺ and Na⁺ ([Ca]_i, [Na]_i). The magnitude of the increases in [Ca]_i and [Na]_i due to A23187-stimulation further indicate that when presented with a calcium challenge the acinar cells continue to regulate [Ca]_i close to physiological levels and suggest that the observed increases in ionized calcium could reflect much larger increases in complexed Ca²⁺. ACh-stimulation following removal of either extracellular Na⁺ or Ca²⁺ ions, eliminated the intracellular increases found when the removed ions is present, but did not affect the increases usually found with the other ion. The independence of the permeability changes to either the presence of Ca²⁺ or Na⁺ indicates the ACh-induced currents carried by Na⁺ and Ca²⁺ are also independent. The selective translocation of Na⁺ and Ca²⁺ during acetylcholine-stimulation in a manner analogous to the changes observed when ionophore A23187 was used as stimulus, indicates the ability of the activated acinar membrane to function as an ionophore.     

Loss of inorganic ions from host cells infected with Chlamydia psittaci

Mouse fibroblasts (L cells) infected with the 6BC strain of Chlamydia psittaci released potassium ion (K⁺) into the extracellular milieu in a way that depended on size of inoculum and time after infection. When the multiplicity of infection was 500 to 1,000 50% infectious units (ID₅₀) per L cell, loss of intracellular K⁺ was first apparent 4 to 10 h after infection and was nearly complete at 6 to 20 h. Magnesium ion and inorganic phosphate (P_i) were also released. Similar multiplicities of ultraviolet-inactivated C. psittaci also caused release of K⁺. Leakage of inorganic ions probably resulted from immediate damage to the host-cell plasma membrane during ingestion of large numbers of chlamydiae. With multiplicities of 1 to 50 ID₅₀ per L cell, ingestion of C. psittaci was not by itself enough to cause release of K⁺ and P_i from infected L cells. There was a delay of 36 to 72 h between infection and massive leakage of intracellular ions during which time the chlamydiae multiplied extensively. Fifty ID₅₀ of ultraviolet-inactivated C. psittaci per L cell did not bring about significant leakage of K⁺, even after 72 h. The mechanism whereby these multiplicities of infection destroy the ability of host cells to retain intracellular molecules is not known. HeLa 229 cells also released K⁺ and P_i after infection, but these losses occurred more slowly than in comparably infected L cells, possibly because C. psittaci did not multiply as extensively in HeLa cells as it did in L cells. The significance of the inability of chlamydiae-infected cells to regulate the flow of molecules through their plasma membranes is discussed.     

Releasing Effect of Calcium and Phosphate on Catechol-amines,ATP, and Protein from Chromaffin Cell Granules

Addition of Ca²⁺3 mM to isolated bovine adrenal niedullary granules incubated in 130 mM K-phosphate buffer pH 6.8–7.2 causes a rapid initial release of noradrenaline (NA), adrenaline (A), ATP and soluble protein. The effect is increased by addition of 1–6 mg/ml of RNA and inhibited by 1–6 mM Mg²⁺. The effect of Ca²⁺is dependent on the presence of phosphate ions in the incubation medium and does not occur in sucrose, RCI or NaCl. Addition of freshly precipitated calcium phosphate is also effective in inducing release, but addition of CaHPO₄ or Ca₂P₂O₇ had no effect. CaCl₂ 0.3–1 mM did not increase the release but was effective together with 1–6 mg/ml of RNA. In the absence of phosphate ions Ca²⁺and Mg²⁺as well as the divalent ions Ba²⁺and Sr²⁺inhibited the release. The catecholamine releasing effect of Ca²⁺in the presence of phosphate is reduced by 2 mM ATP and almost completely prevented by ATP-Mg²⁺. It is suggested that the increased outflow of granular contents is due to membrane alterations induced by Ca-phosphate.     

The effects of thapsigargin on [Ca2+]i in isolated rat mesenteric artery vascular smooth muscle cells

Summary The effects of thapsigargin were studied on single cells isolated from side branches of the rat mesenteric artery. Thapsigargin (150 nM) produced a transient increase of [Ca²⁺]_i. This transient rise of [Ca²⁺]_i was unaffected by removing external Ca²⁺ ions. This suggests that thapsigargin is releasing Ca²⁺ ions from an intracellular store. In the absence of thapsigargin both noradrenaline and caffeine also produced a transient increase of [Ca²⁺]_i. These increases were abolished by prior exposure to thapsigargin. Correspondingly, the effects of thapsigargin were abolished by prior exposure to caffeine. These results show that thapsigargin releases Ca²⁺ from the noradrenaline and caffeine-sensitive stores.